Homemade solar concentrator from a mirror film. DIY solar concentrator

In this scheme, mirror 1 is the lens, also called the main mirror. This mirror is parabolic or spherical. Mirror 2 is called a diagonal mirror - this mirror directs the beam of reflected rays through the eyepiece to the observer. The element marked with the number 3 is the ocular assembly.

The focus of the main mirror and the focus of the eyepiece inserted into the eyepiece tube must match. The focus of the primary mirror is defined as the apex of the cone of rays reflected by the mirror.

An ordinary household flat mirror is not always suitable for use as a diagonal mirror in a homemade telescope - an optically more accurate surface is needed for a telescope. Therefore, a flat surface of a plano-concave or plano-convex optical lens can be used as a diagonal mirror if this plane is first coated with a layer of silver or aluminum.

The dimensions of a flat diagonal mirror for a homemade telescope are determined from the graphical construction of the cone of rays that are reflected by the main mirror. With a rectangular or elliptical mirror, the sides or axes are related to each other as 1:1.4.

The objective and eyepiece of a self-made reflecting telescope are mounted mutually perpendicular in the telescope tube. To mount the main mirror of a homemade telescope, a frame, wooden or metal, is required.

The pipe of a homemade telescope is made from a piece of metal pipe, from several layers of cardboard glued together. You can also make a metal-cardboard pipe.

Three layers of thick cardboard should be glued together with carpentry or casein glue, then insert the cardboard tube into the metal stiffening rings. They also make a bowl for the frame of the main mirror of a homemade telescope and a pipe cover from metal.

The length of the tube (tube) of a self-made reflecting telescope should be equal to the focal length of the main mirror, and the inner diameter of the tube should be 1.25 of the diameter of the main mirror. From the inside, the tube of a home-made reflecting telescope should be “blackened”, i.e. cover with matte black paper or paint with matte black paint.

Before use, a home-made reflecting telescope must be installed on a special stand - a mount.

Now let's take a closer look at how to grind a mirror:

If the focal length of the main mirror with a diameter of 100 mm is more than 700 mm, and with a diameter of 120 mm - more than 900 mm, then it is better to make the mirror surface not parabolic, but spherical, which is much easier.
For the manufacture of such a spherical mirror, two disks are needed (with a diameter of 100 mm, a thickness of at least 8-10 mm, with a diameter of 120 mm, about 12-14 mm) of well-annealed glass, for example, mirror, display, porthole. If there is a thick mirror glass, you can cut the discs yourself with a tubular drill. It is bent from a strip of iron, steel or other not very soft metal. The wall thickness of the drill is 1-2 mm.

Grind discs on a machine. On a thick board - the base - a rotating round or six-, octagonal table is fixed. In its center, an axis rotating at the base is tightly fixed. The table can be supported by 3 steel balls “recessed” in the base. It is very convenient to work on such a machine: instead of walking around the table yourself, you can turn the machine table.

To speed up the process of rough grinding, ring grinding is used in modern amateur practice. As a ring, take a piece of thick-walled cast iron pipe. The diameter of the ring is about half the diameter of the mirror. Putting the future mirror in place of the grinder, grind it with a ring, smearing the slurry of abrasive with water. Make sure that the ring does not extend beyond the edge of the grinder. The ring and the machine table must rotate uniformly in opposite directions all the time. When grinding with a ring, a recess in the glass is obtained much faster than when grinding glass with glass. During further grinding, in addition to the glass grinder, grinders are used, the bases of which are made of a variety of materials: metal, getinax, textolite, cast from a mixture of cement with sand or cement with alabaster. A tree impregnated with a water-repellent composition is also used. Squares of glass or plexiglass are glued onto the base of such a grinder. Special metal grinders are also used.

Their bases, having the form of a sphere, are machined on a lathe. The use of the grinders described above allows us to limit ourselves to one glass disk - the future mirror.

Approaching or moving away from the mirror, ensure that the artificial star fills the entire surface of the mirror with its light. If we now slowly cross the top of the cone of rays with the “Foucault knife”, then the entire mirror will “extinguish” at the same time. This means that all the rays reflected from the mirror converge at one point. If the curvature of the mirror surface deviates from the specified one, then you will see a "shadow picture", which is used to judge the shape of the surface. Correct the surface of the mirror by further polishing, changing the nature of the movements of the mirror (strokes) or the shape of the polishing pad. The real deviations of the surface of the mirror you made from the sphere are measured in fractions of a micron.

The concave spherical surface of a polished mirror reflects only about 5% of the light falling on it. Therefore, it must be covered with a reflective layer of aluminum or silver. The mirror is aluminized only in a special installation, and you can silver it at home.

In a Newtonian reflecting telescope, a diagonal flat mirror deflects sideways the cone of rays reflected from the main mirror. It is very difficult to make a good flat mirror yourself. Instead of this mirror, use a prism with total internal reflection from prism binoculars. With a main mirror with a diameter of 100-120 mm, the dimensions of the rectangular planes of the prism, located at an angle of 90 °, are between 20x20 mm and 25x25 mm.

As a flat diagonal mirror, you can also use the flat surface of a lens, the surface of a light filter from a camera, or any other optically accurate plane. Cover it with a layer of silver or aluminize.

How to build a solar water heater. It is more correct to call it a parabolic solar concentrator. Its main advantage is that the mirror reflects 90% of the solar energy, and its parabolic shape concentrates this energy at one point. This installation will work effectively in most regions of Russia, up to 65 degrees north latitude.

To assemble the collector, we need a few basic things: the antenna itself, the sun tracking system and the heat exchanger-collector.

parabolic antenna.

You can use any antenna - iron, plastic or fiberglass. The antenna must be panel type, not mesh. Antenna area and shape are important here. It must be remembered that the heating power = the surface area of ​​the antenna. And that the power collected by an antenna with a diameter of 1.5 m will be 4 times less than the power collected by an antenna with a mirror area of ​​3 m.

You will also need a rotary mechanism for the antenna assembly. It can be ordered on Ebay or Aliexpress.

You will need a roll of aluminum foil or lavsan mirror film used for greenhouses. Glue with which the film will be glued to the parabola.

Copper tube with a diameter of 6 mm. Fittings for connecting hot water to a tank, to a pool, or where you will use this design. The author purchased the rotary tracking mechanism on EBAY for $30.

Step 1 Modifying the Antenna for Focusing solar radiation instead of radio waves.

All you have to do is attach a lavsan mirror film or aluminum foil to the antenna mirror.

This is almost as easy to do as it sounds. It is only necessary to take into account that if the antenna, for example, has a diameter of 2.5 m, and the film is 1 m wide, then it is not necessary to cover the antenna with a film in two passes, folds and irregularities will form, which will worsen the focusing of solar energy. Cut it into small strips and fix it to the antenna with glue. Make sure the antenna is clean before sticking the film. If there are places where the paint is swollen, clean them with sandpaper. You need to smooth out all the irregularities. Please note that the LNB must be removed from its place, otherwise it may melt. After sticking the film and installing the antenna in place, do not put your hands or face near the head attachment point - you risk serious sunburn.

Step 2 tracking system.

As it was written above - the author bought a tracking system on Ebay. You can also look for rotary sun tracking systems. But I found a simple circuit with a penny price that tracks the position of the sun quite accurately.

Parts list:
(downloads: 428)
* U1/U2 - LM339
* Q1 - TIP42C
*Q2-TIP41C
*Q3-2N3906
*Q4-2N3904
* R1 - 1meg
* R2 - 1k
* R3 - 10k
* R4 - 10k
* R5 - 10k
* R6 - 4.7k
* R7 - 2.7k
* C1 - 10n ceramic
* M - DC motor up to 1A
* LEDs - 5mm 563nm

Itself can be made on the basis of the front hub of a VAZ car.

For those interested, the photo was taken from here:

Step 3 Creating a heat exchanger-collector

To make a heat exchanger, you will need a copper tube rolled into a ring and placed at the focus of our concentrator. But first we need to know the size of the focal point of the dish. To do this, you need to remove the LNB converter from the dish, leaving the converter mounts. Now you need to turn the plate in the sun, after fixing a piece of the board at the place where the converter is attached. Hold the board in this position for a while until smoke appears. This will take approximately 10-15 seconds. After that, unscrew the antenna from the sun, remove the board from the mount. All manipulations with the antenna, its turns, are carried out so that you do not accidentally stick your hand into the focus of the mirror - this is dangerous, you can get burned badly. Let it cool down. Measure the size of the burnt piece of wood - this will be the size of your heat exchanger.

Step 4 Putting it all together and trying it out.

I have a simple Celestron PowerSeeker 127 EQ telescope, like this one in the photo above. My wife gave it to me for my birthday. It was a rather spontaneous gift like this: "I don't know what to give you, look at the store, let's go look." In principle, I was very pleased with such a gift, the thing is very interesting. However, while using it, I realized that I wanted more. This PowerSeeker 127EQ telescope has a number of significant design flaws which, due to my inexperience, I simply did not know. The main disadvantage is the spherical main mirror and the corrective lens for it. As a result, an overcomplicated optical design, inaccuracies in the fit of the corrective lens, which, moreover, is not of high quality. In general, the quality of the observed image with such a mirror diameter, I think, could be better.

I thought that I need another telescope. This is a normal situation. They say that no matter what telescope an amateur has, he always dreams of the best. And then the question arises: buy or make yourself? The answer is not really obvious. Is it easier to buy, maybe even cheaper? Building it yourself in the absence of experience is a difficult technical task, it is not known whether it will work at all and it is not clear whether it will be cheaper than just buying it.

I entered the slippery path of independent telescope construction. Next, I’ll talk about my first steps in this direction, but I immediately warn you that don’t wait to read an article with a happy ending just yet. I am very far from it (if it happens at all).

So, you need to start with the study of theory.

In my opinion, there is nothing better than the book "Telescopes for Astronomy Lovers", L.L. Sikoruk, 1982. Despite the fact that the book is more than thirty years old, I have not seen a more detailed presentation “from and to”. There is also a book by M. S. Navashin "Amateur Astronomer's Telescope", 1979. Also useful.

In addition to these very useful books, of course, you can and should visit astroforums. for example, this one. Here you can ask a question and read who does what and how.

Last resort: youtube.com. It may seem strange, but telescopes around the world are built by so many people. Some even video blog and show the manufacturing process. Keywords for YouTube search: mirror grinding.

In general, I would say that the niche of amateur telescope construction in Russia seems to be completely empty (but this is not accurate). In Europe and America, there are special shops that sell blanks for mirrors (mirror blanks), and grinding powders, and tools and kits for making mirrors (teleskope mirror kit).

We now, of course, are not in the 79th or 82nd year, but where can I get a blank for the telescope mirror? Or where to get sanding powder? I found several optical factories, but they seem to have absolutely no interest in private customers. Probably their main customer is the state represented by the military-industrial complex. I wanted to buy a blank mirror - a disk with a diameter of 200 millimeters - and I was told that it would cost about thirty thousand without postage. Perhaps there is a very high-quality optical glass, but I just don’t understand an amateur (without irony, I know that exceptional quality may be required somewhere).

To tell the truth, for thirty thousand you can buy a ready-made large mirror somewhere in great China.

In general, I decided to do it from improvised materials, as Sikoruk advised to do in his book. The material at hand is display glass (but not tempered). I need to cut several discs out of 10mm thick glass and then glue them together liquid glass. In his book, Sikoruk writes and substantiates the necessary thickness of the main mirror, depending on its diameter.

Epic one. Glass cutting

I went to the glazier and asked him to cut me rectangular pieces of 10 mm glass approximately 250x250 millimeters, but they must all be from one sheet in order to be sure of the same properties of all blanks.

I went to the store and bought a couple of aluminum pans with an internal diameter of 180 millimeters. This is exactly what I planned to make a telescope To tell the truth, Sikoruk advises making the first telescope no more than 100 millimeters and gaining experience on it, but no, we are smart, we do 180 right away.

The pan was sawn and a load and two protruding bolts were screwed to the bottom.

This will be the cutter.

Next comes the long and painful process of manufacturing a machine for cutting a workpiece. Here the engine from the old one is useful washing machine, a pulley from it, some old gearbox, pieces of plywood, studs, nuts and other nonsense.
In general, it looks like this:

The pot lid is glued to the glass with silicone and the edges are rounded. It serves as a centering element for my cutter. The cutter, well, that is, half a pan is put on top and is driven by a gearbox from the motor.

This thing works like this (my video):

While working under the edges of the cutter, you need to constantly add abrasive. I worked with the abrasive for five to seven minutes, the abrasive was worn out and mixed with crumbs of glass and aluminum. Rinse off the old abrasive and pour in a new one. I then got used to doing all this on the fly without turning off the engine. It worked, washed off and then poured a new abrasive with a spoon.

That's not very Good photo, but you can see how much the “cutter” plunged into the thickness of the glass:

I mined the abrasive in the same way as our distant ancestors did in the time of mammoths. I had a piece of the old grinding wheel. I crushed it with a hammer on an anvil.

The resulting pieces were still pounded with a hammer, the crumbs were collected in a jar - a coarse abrasive powder turned out. Of course, at this stage, such savagery is still acceptable, but then we will have to improve the culture of production.

As a result, one 180 mm disk from a 10 mm sheet on my machine is cut in about three to three and a half hours. I cut out four disks:

My wealth:

According to my plan, I will glue them in pairs with liquid glass, I will process the edges with epoxy, as Seakoruk advises, and I will have two 180 mm primary mirror blanks. Next, I will start sharpening them and probably ruin one. As for the second one, I hope it works.

I have already purchased a set of grinding powders for this mission:

But then another story begins. Need to sharpen. This is done in several stages: rough molding-peeling, grinding and then polishing. I'm honestly stuck at this point. Here are some illustrations from the book Telescopes for Astronomy Lovers:

Peeling:

Grinding:

Typical mistakes:

Unfortunately, despite detailed explanations in the book of Sikoruk and from other sources, I do not have an absolutely accurate idea of ​​\u200b\u200bhow this should be done correctly. The problem is that you need to execute the parabola with very high accuracy: errors, bumps or pits on the primary mirror must be less than 1/8 of the wavelength of light. The accuracy of the parabola must be at least 0.05 µm.

Here is how Sikoruk writes in his book:

It is difficult to divide the process of figuration and shadow tests into components - this is a single creative process, where not only knowledge, but also intuition often plays a decisive role. In general, this process is so interesting in itself that the author, for example, often does not rush to finish, trying to work this way and that, finding great pleasure in the process of figuring, although, no doubt, the view of a completely flat shadow picture is an amazing sight.

In the process of polishing, according to J. Matthewson, "there is always an element of mysticism." This is partly due to the fact that the polishing process is largely insufficiently studied, but partly also to the fact that the master himself often wants a little mysticism, when figuration ceases to be just a technology, but becomes largely an art. It was not for nothing that D. D. Maksutov said that the optician prefers to "conjure" over the home-made resin of the polishing pad, not trusting the factory resin. (However, if you have the opportunity to purchase a factory polishing resin, you should do it). Often the success of a business is decided by a creative impulse, and in order to have more time for creativity, it is necessary to prevent the causes that clearly lead to trouble.

In fact, of course, the same book by Seekoruk tells how to control the shape of a mirror. To do this, you must first build a special "shadow device". However, with the help of this device, I think it is possible to detect zonal errors, but it is absolutely not clear how to modify the polishing pad so that zonal errors are corrected during further polishing.

I watched a lot of video demonstrations on YouTube: there is both shaping and grinding and the so-called "parabolization" with the magic stroke "W".

Here are some colorful videos:
Rough processing:

Mirror grinding: 200 f/5 fine grinding:

Still people build machines for machining mirrors:

From all this it turns out that everyone does as he thinks, but how to do it in such a way as to guarantee the result? There is something to think about here...

After quite some thought, I decided before sharpening I should try to make a software model of the entire grinding process. For some reason I thought it would be pretty easy to do. I thought that I would make a grinding machine, something like the one in the last video.

The mirror blank should rotate slowly at the bottom, and, for example, a steel peeling ring will move from above with reciprocating movements using a crank mechanism.

I decided that the program model could be very simple: you need to calculate the time spent by each point of the mirror blank under the surface of the peeling ring. You can try to read not the entire surface of the workpiece, but only one cut-radius.

This video is formed from snapshots of the virtual roughing process in my program:

I thought that by choosing the length of the stroke in the software model, the length of the arms of the crank mechanism (and its movement is far from a sinusoid), I would be able to tell exactly how to sharpen in order to reach the parabola.

Unfortunately, I must say that the further I delve into the problem, the more I understand that my virtual programming model does not work at all. I do not take into account too many parameters that affect the speed of glass grinding: for example, I do not take into account the speed of rubbing parts, but it is different in the center and along the edges. Then I do not yet take into account the pressure of the peeling ring on the workpiece, and this apparently needs to be done, since in the process of work the shape of the workpiece changes, which means that the distribution of friction forces over the workpiece surface also changes.

When I wrote this article, I even thought to give here the entire source code of my program (C / C ++), however, what's the point if the program does not work?

At the moment, I am engaged in a radical rewriting of my software and I intend to make a program model of the mirror figuring process. Perhaps, if I still succeed, I will publish my code.

It's safe to say that everyone has ever dreamed of taking a closer look at the stars. With binoculars or a spyglass, you can admire the bright night sky, but you are unlikely to be able to see anything in detail with these devices. Here you need more serious equipment - a telescope. To have such a miracle of optical technology at home, you need to pay a large amount, which not all lovers of beauty can afford. But do not despair. You can make a telescope with your own hands, and for this, no matter how absurd it may sound, it is not necessary to be a great astronomer and designer. If only there was a desire and an irresistible craving for the unknown.

Why should you try making a telescope? We can definitely say that astronomy is a very complex science. And it requires a lot of effort from the person involved in it. It may happen that you get an expensive telescope, and the science of the Universe will disappoint you, or you simply realize that this is absolutely not your job. In order to figure out what's what, it's enough to make a telescope for an amateur. Observing the sky through such an apparatus will allow you to see many times more than through binoculars, and you can also figure out if this activity is interesting for you. If you get excited about studying the night sky, then, of course, you cannot do without a professional apparatus. What can you see with a homemade telescope? Descriptions of how to make a telescope can be found in many textbooks and books. Such a device will allow you to clearly see the lunar craters. With it, you can see Jupiter and even see its four main satellites. The rings of Saturn familiar to us from the pages of textbooks can also be seen with a telescope made by ourselves.

In addition, many more celestial bodies can be seen with your own eyes, for example, Venus, a large number of stars, clusters, nebulae. A little about the structure of the telescope The main parts of our unit are its lens and eyepiece. With the help of the first detail, the light emitted by celestial bodies is collected. How far away bodies can be seen, as well as what the magnification of the device will be, depends on the diameter of the lens. The second member of the tandem, the eyepiece, is designed to increase the resulting image so that our eye can admire the beauty of the stars. Now about the two most common types of optical devices - refractors and reflectors. The first type has a lens made of a lens system, and the second has a mirror lens. Lenses for a telescope, unlike a reflector mirror, can be easily found in specialized stores. Buying a mirror for a reflector will cost a lot, and making it yourself will be impossible for many.

Therefore, as it has already become clear, we will assemble a refractor, and not a mirror telescope. Let's finish the theoretical digression with the concept of telescope magnification. It is equal to the ratio of the focal lengths of the lens and the eyepiece. Personal experience: how I did laser vision correction Actually, I did not always radiate joy and self-confidence. But first things first .. How to make a telescope? We select materials In order to start assembling the device, you need to stock up on a 1-diopter lens or its blank. By the way, such a lens will have a focal length of one meter. The diameter of the blanks will be about seventy millimeters. It should also be noted that it is better not to choose spectacle lenses for a telescope, since they are mostly concave-convex in shape and are not suitable for a telescope, although if they are at hand, then you can use them. It is recommended to use long focal length biconvex lenses. As an eyepiece, you can take an ordinary magnifying glass of a thirty-millimeter diameter. If it is possible to get an eyepiece from a microscope, then, undoubtedly, it is worth using it. It's great for a telescope too. What to make a case for our future optical assistant? Perfect for two pipes. different diameter from cardboard or thick paper. One (the one that is shorter) will be inserted into the second, with a larger diameter and longer.

A pipe with a smaller diameter should be made twenty centimeters long - this will eventually be an ocular node, and it is recommended to make the main one meter long. If you don’t have the necessary blanks at hand, it doesn’t matter, the case can be made from an unnecessary roll of wallpaper. To do this, the wallpaper is wound in several layers to create the desired thickness and rigidity and glued. How to make the diameter of the inner tube depends on which lens we use. Telescope stand Very important point in creating your telescope - preparing a special stand for it. Without it, it will be almost impossible to use it. There is an option to install the telescope on a tripod from the camera, which is equipped with a moving head, as well as fasteners that will allow you to fix various positions of the body. Assembling the telescope The objective lens is fixed in a small tube with the bulge outward. It is recommended to fix it with the help of a frame, which is a ring similar in diameter to the lens itself.

You have a wonderful blank for the main mirror. But only if it's K8 lenses. Because in condensers (and these are undoubtedly condenser lenses) they often put a pair of lenses, one of which is from a crown, the other from a flint. A flint lens as a blank for the main mirror is absolutely unsuitable for a number of reasons (one of which is its high sensitivity to temperature). A flint lens is great as a base for a polishing pad, but it will not work with it, since the flint has a much greater hardness and abradability than a crown. In this case, use a plastic grinder.

Secondly, I strongly advise you to carefully read not only the book by Sikoruk, but also the "Telescope of an amateur astronomer" by M.S. Navashina. And as far as tests and measurements of the mirror are concerned, one should be guided precisely by Navashin, in whom this aspect is described in great detail. Naturally, it is not worth making a shadow device "according to Navashin" exactly, since now it is easy to introduce such improvements into its design as using a powerful LED as a light source (which will significantly increase the light intensity and the quality of measurements on an uncoated mirror, and also allow bring the "star" close to the knife; it is advisable to use a rail from an optical bench as a base, etc.). The manufacture of a shadow device must be approached with all the attention, since it is how well you make it that will determine the quality of your mirror.

In addition to the aforementioned rail from the optical bench, a useful "swag" for its manufacture is a support from a lathe, which will be a wonderful device for smooth movement of the Foucault knife and at the same time for measuring this movement. An equally useful find would be a ready-made slit from a monochromator or diffractometer. I also advise you to adapt a webcam to the shadow device - this will eliminate the error from the position of the eye, reduce convection interference from your body heat, and in addition, it will allow you to register and store all shadow pictures during the process of polishing and figuring the mirror. In any case, the base for the shadow device must be reliable and heavy, the fastening of all parts must be ideally rigid and durable, and the movement must be without backlash. Organize a pipe or tunnel along the entire path of the rays - this will reduce the effect of convection currents, and in addition, it will allow you to work in the light. In general, convection currents are the scourge of any mirror testing methods. Fight them with all possible means.

Invest in good quality abrasives and resins. Cooking resin and elutriating abrasives is, firstly, an unproductive expenditure of energy, and secondly, bad resin is a bad mirror, and bad abrasives are a lot of scratches. But the grinding machine can and should be the most primitive, the only requirement for it is the impeccable rigidity of the structure. Here, a wooden barrel covered with rubble is absolutely ideal, around which Chikin, Maksutov and other "founding fathers" used to walk around. A useful addition to Chikin's barrel is the "Grace" disk, which allows you not to wind kilometers around the barrel, but to work while standing in one place. A barrel for peeling and rough grinding is better to equip on the street, but fine grinding and polishing is a matter for a room with a constant temperature and without drafts. An alternative to a barrel, especially at the stage of fine grinding and polishing, is the floor. Of course, it is less convenient to work on your knees, but the rigidity of such a "machine" is ideal.

Need Special attention devote to fixing the workpiece. A good option for unloading the lens is gluing a small "patch" in the center and three stops near the edges, which should only touch, but not put pressure on the workpiece. Piglet needs to be ground on a plane and brought to No. 120.

To prevent scratches and chips, it is necessary to make a chamfer along the edge of the workpiece before peeling and bring it to fine grinding. The width of the chamfer should be calculated so that it remains until the end of the work with the mirror. If the chamfer "ends" in the process, it must be resumed. The chamfer must be uniform, otherwise it will be a source of astigmatism.

The most rational is peeling with a ring, or with a reduced grinder in the “mirror from below” position, but given the small size of the mirror, you can also do it according to Navashin - a mirror from above, a grinder of normal size. Silicon carbide or boron carbide is used as an abrasive. When peeling, one must beware of picking up astigmatism and "going away" into a hyperboloid form, to which such a system has a clear tendency. The alternation of a normal stroke with a shortened one helps to avoid the latter, especially towards the end of the peeling. If, during roughing, a surface that is as close to a sphere as possible is initially obtained, this will dramatically speed up all further work on grinding.

Abrasives when grinding - starting from the 120th number and smaller, it is better to use electrocorundum, and larger - carborundum. Main characteristic abrasives, to which one must strive, is the narrowness of the particle distribution spectrum. If the particles in a given number of abrasive vary in size, then larger grains are the source of scratches, and smaller grains are the source of local errors. And with abrasives of this quality, their "ladder" should be much flatter, and we will come to polishing with "waves" on the surface, which we will then get rid of for a long time.

A shamanic trick against this with not the best abrasives is to grind the mirror with an even finer abrasive before changing the number to a thinner one. For example, instead of the series 80-120-220-400-600-30u-12u-5u, the series will be: 80-120-400-220-600-400-30u-600... and so on, and these intermediate steps short. Why it works, I don't know. With a good abrasive, you can grind after the 220th number immediately with thirty microns. It is good to add Fairy abrasives to coarse (up to No. 220) abrasives diluted with water. It makes sense to look for micron powders with the addition of talc (or add it yourself, but you need to be sure that talc is abrasive-sterile) - it reduces the likelihood of scratches, facilitates the grinding process and reduces biting.

Another tip that allows you to control the shape of the mirror even at the stage of grinding (not even fine) is to polish the surface by grinding it with suede with polyrite to a shine, after which you can easily determine the focal length by the Sun or a lamp and even (at finer stages of grinding) get shadow picture. A sign of the accuracy of the spherical shape is also the uniformity of the ground surface and the rapid uniform grinding of the entire surface after changing the abrasive. Vary the length of the stroke within small limits - this will help to avoid a "broken" surface.

The process of polishing and figuring is probably described so well and in detail that it is more reasonable not to go into it, but to refer it to Navashin. True, he recommends crocus, but now everyone uses polyrite, otherwise everything is the same. Crocus, by the way, is useful for figuration - it works more slowly than polyrite, and there is less risk of "missing" desired shape.

Directly behind the lens, further along the pipe, it is necessary to equip the diaphragm in the form of a disk with a thirty-millimeter hole strictly in the middle. Aperture is designed to negate the distortion of the picture that appears in connection with the use of a single lens. Also, setting it will affect the reduction of light that the lens receives. The telescope lens itself is mounted near the main tube. Naturally, in the ocular assembly one cannot do without the eyepiece itself. First you need to prepare fasteners for it. They are made in the form of a cardboard cylinder and are similar to the eyepiece in diameter. Fastening is established in a pipe by means of two disks. They are the same diameter as the cylinder and have holes in the middle. Setting up the device at home It is necessary to focus the image using the distance from the lens to the eyepiece. To do this, the ocular assembly moves in the main tube.

Since the pipes must be well pressed together, the required position will be securely fixed. The tuning process is convenient to carry out on large bright bodies, for example, the Moon, and a neighboring house will also do. When assembling, it is very important to ensure that the lens and the eyepiece are parallel and their centers are on the same straight line. Another way to make a telescope with your own hands is to change the aperture size. By varying its diameter, you can achieve the optimal picture. Using optical lenses of 0.6 diopters, which have a focal length of about two meters, you can increase the aperture and make the zoom on our telescope much larger, but it should be understood that the body will also increase.

Beware of the Sun! By the standards of the Universe, our Sun is far from the brightest star. However, for us it is a very important source of life. Naturally, having a telescope at their disposal, many will want to take a closer look at it. But you need to know that it is very dangerous. After all, sunlight, passing through the optical systems we have built, can be focused to such an extent that it will be able to burn through even thick paper. What can we say about the delicate retina of our eyes. Therefore, it is very important to remember important rule: you can’t look at the Sun with zooming devices, especially with a home telescope, without special protective equipment.

First of all, you need to purchase a lens and an eyepiece. As a lens, you can use two glasses for glasses (menisci) of +0.5 diopters, placing them with their convex sides one outward and the other inward at a distance of 30 mm from one another. Between them, put a diaphragm with a hole with a diameter of about 30 mm. This is the last resort. But it is better to use a long-focal biconvex lens.

For an eyepiece, you can take an ordinary magnifying glass (loupe) 5-10 times with a small diameter of about 30 mm. As an option, there may also be an eyepiece from a microscope. Such a telescope will give a magnification of 20-40 times.

For the case, you can take thick paper or pick up metal or plastic tubes (there should be two of them). A short tube (about 20 cm, ocular assembly) is inserted into a long one (about 1m, main). The inner diameter of the main tube should be equal to the diameter of the spectacle lens.

The lens (spectacle lens) is mounted in the first tube with the convex side outward using a frame (rings with a diameter equal to the diameter of the lens and a thickness of about 10 mm). Immediately behind the lens, a disk is installed - a diaphragm with a hole in the center with a diameter of 25 - 30 mm, this is necessary in order to reduce significant image distortions obtained by a single lens. The lens is mounted closer to the edge of the main tube. The eyepiece is installed in the eyepiece node closer to its edge. To do this, you will have to make a mount for the eyepiece out of cardboard. It will consist of a cylinder, equal in diameter to the eyepiece. This cylinder will be attached to inside pipes with two discs with a diameter equal to the inner diameter of the ocular assembly with a hole equal in diameter to the eyepiece.

Focusing is done by changing the distance between the lens and the eyepiece due to the movement of the eyepiece assembly in the main tube, and fixation will occur due to friction. Focusing is best done on bright and large objects: the moon, bright stars, nearby buildings.

When creating a telescope, it is necessary to take into account that the lens and the eyepiece must be parallel to each other, and their centers must be strictly on the same line.

Making a homemade reflecting telescope

There are several systems of reflecting telescopes. It is easier for an amateur astronomer to make a Newtonian reflector.

Plano-convex condenser lenses for photographic enlargers can be used as mirrors by processing their flat surface. Such lenses with a diameter of up to 113 mm can also be purchased at photo stores.

The concave spherical surface of a polished mirror reflects only about 5% of the light falling on it. Therefore, it must be covered with a reflective layer of aluminum or silver. It is impossible to aluminize a mirror at home, but it is quite possible to silver it.

In a Newtonian reflecting telescope, a diagonal flat mirror deflects sideways the cone of rays reflected from the main mirror. It is very difficult to make a flat mirror yourself, so use a prism with total internal reflection from prism binoculars. You can also use a flat lens surface for this purpose, the surface of a light filter from a camera. Cover it with silver.

Eyepiece set: weak eyepiece with a focal length of 25-30 mm; average 10-15 mm; strong 5-7 mm. You can use eyepieces from a microscope, binoculars, lenses from small-format movie cameras for this purpose.

Mount the main mirror, flat diagonal mirror and eyepiece in the telescope tube.

For a reflecting telescope, make a parallax tripod with a polar axis and a declination axis. The polar axis should be directed to the North Star.

Such means are light filters and a method of projecting an image onto a screen. What if you didn’t manage to assemble a telescope with your own hands, but you really want to look at the stars? If suddenly, for some reason, assembling a homemade telescope is impossible, then do not despair. You can find a telescope in the store for a reasonable price. The question immediately arises: "Where are they sold?" Such equipment can be found in specialized stores of astro-devices. If there is no such thing in your city, then you should visit a photographic equipment store or find another store selling telescopes. If you are lucky - there is a specialized store in your city, and even with professional consultants, then you are definitely there. It is recommended to look at the review of telescopes before the trip. First, you will understand the characteristics of optical devices. Secondly, it will be more difficult for you to deceive and slip low-quality goods.

Then you will definitely not be disappointed in the purchase. A few words about buying a telescope through the World Wide Web. This type of shopping is becoming very popular in our time, and it is possible that you will use it. It is very convenient: you look for the device you need, and then order it. However, you can stumble upon such a nuisance: after a long selection, it may turn out that the product is no longer available. A much more unpleasant problem is the delivery of goods. It's no secret that the telescope is a very fragile thing, so only fragments can be brought to you. It is possible to buy a telescope with hands.

This option will allow you to save a lot, but you should be well prepared so as not to buy a broken item. A good place to find a potential seller is the astronomy forums. Price for a telescope Consider some price categories: About five thousand rubles. Such a device will correspond to the characteristics that a do-it-yourself telescope has at home. Up to ten thousand rubles. This device will certainly be more suitable for high-quality observation of the night sky. The mechanical part of the case and the equipment will be very scarce, and you may have to spend money on some spare parts: eyepieces, filters, etc. From twenty to one hundred thousand rubles. This category includes professional and semi-professional telescopes.

Amateur astronomers build homemade reflecting telescopes mainly according to Newton's system. It was Isaac Newton who invented the first reflecting telescope around 1670. This allowed him to get rid of chromatic aberrations (they lead to a decrease in the clarity of the image, to the appearance of colored contours or stripes on it, which are not present on a real object) - the main drawback of the refracting telescopes that existed at that time.

diagonal mirror - this mirror directs the beam of reflected rays through the eyepiece to the observer. The element marked with the number 3 is the ocular assembly.

The focus of the main mirror and the focus of the eyepiece inserted into the eyepiece tube must match. The focus of the primary mirror is defined as the apex of the cone of rays reflected by the mirror.

The diagonal mirror is made in small sizes, it is flat and can have a rectangular or elliptical shape. A diagonal mirror is mounted on the optical axis of the main mirror (objective), at an angle of 45° to it.

An ordinary household flat mirror is not always suitable for use as a diagonal mirror in a homemade telescope - an optically more accurate surface is needed for a telescope. Therefore, a flat surface of a plano-concave or plano-convex optical lens can be used as a diagonal mirror if this plane is first coated with a layer of silver or aluminum.

The dimensions of a flat diagonal mirror for a homemade telescope are determined from the graphical construction of the cone of rays that are reflected by the main mirror. With a rectangular or elliptical mirror, the sides or axes are related to each other as 1:1.4.

The objective and eyepiece of a self-made reflecting telescope are mounted mutually perpendicular in the telescope tube. To mount the main mirror of a homemade telescope, a frame, wooden or metal, is required.

To make a wooden frame for the main mirror of a homemade reflecting telescope, you can take a round or octagonal plank with a thickness of at least 10 mm and 15-20 mm more than the diameter of the main mirror. The main mirror is fixed on this plate with 4 pieces of a thick-walled rubber tube, put on screws. For better fixation, plastic washers can be placed under the screw heads (the mirror itself cannot be clamped with them).

The pipe of a homemade telescope is made from a piece of metal pipe, from several layers of cardboard glued together. You can also make a metal-cardboard pipe.

Three layers of thick cardboard should be glued together with carpentry or casein glue, then insert the cardboard tube into the metal stiffening rings. They also make a bowl for the frame of the main mirror of a homemade telescope and a pipe cover from metal.

The length of the tube (tube) of a self-made reflecting telescope should be equal to the focal length of the main mirror, and the inner diameter of the tube should be 1.25 of the diameter of the main mirror. From the inside, the tube of a home-made reflecting telescope should be “blackened”, i.e. cover with matte black paper or paint with matte black paint.

The ocular assembly of a home-made reflecting telescope in the simplest version can be based, as they say, “on friction”: the movable inner tube moves along the stationary outer tube, providing the necessary focusing. The ocular assembly can also be threaded.

Before use, a home-made reflecting telescope must be installed on a special stand - a mount. You can purchase both a ready-made factory mount, and make it yourself, from improvised materials. You can read more about the types of mounts for homemade telescopes in our next materials.

Surely a beginner will not need a mirror device with an astronomical cost. It is simply, as they say, a waste of money. Conclusion In the end, we got acquainted with important information on how to make a simple telescope with your own hands, and some of the nuances of buying a new apparatus for observing stars. In addition to the method that we examined, there are others, but this is a topic for another article. Whether you have built a telescope at home or purchased a new one, astronomy will allow you to immerse yourself in an unknown world and get experiences that you have never experienced before.

A spectacle tube is essentially a simple refractor with a single lens instead of a lens. The rays of light coming from the observed object are collected in the tube by a lens objective. To destroy the iridescent coloring of the image - chromatic aberration - use two lenses from different varieties glass. Each surface of these lenses must have its own curvature, and

all four surfaces must be coaxial. It is almost impossible to make such a lens in amateur conditions. It is difficult to get a good, even a small, lens objective for a telescope.

H0 is another system - a reflecting telescope. or reflector. In it, the lens is a concave mirror, where the exact curvature needs to be given to only one reflective surface. How is it arranged?

Rays of light come from the observed object (Fig. 1). The main concave (in the simplest case, spherical) mirror 1, which collects these rays, gives an image in the focal plane, which is viewed through the eyepiece 3. In the path of the beam of rays reflected from the main mirror, a small flat mirror 2 is placed, located at an angle of 45 degrees to optical axis of the main. It deflects the cone of rays at a right angle so that the observer does not obstruct the open end of the telescope tube 4 with his head. On the side of the tube opposite the diagonal flat mirror, a hole was cut for the exit of the cone of rays and the eyepiece tube 5 was fixed. that the reflective surface is processed with very high accuracy - the deviation from the specified size should not exceed 0.07 microns (seven hundred-thousandths of a millimeter) - the manufacture of such a mirror is quite affordable for a schoolboy.

First, cut out the main mirror.

The main concave mirror can be made from ordinary mirror, table or display glass. It should have sufficient thickness and be well annealed. Poorly annealed glass warps strongly when the temperature changes, and this distorts the shape of the mirror surface. Plexiglas, plexiglass and other plastics are not suitable at all. The thickness of the mirror should be slightly more than 8 mm, the diameter should not exceed 100 mm. Under a piece of a metal pipe of a suitable diameter with a wall thickness of 02-2 mm, a slurry of emery powder or carborundum powder with water is applied. Two disks are cut out of mirror glass. Manually from glass with a thickness of 8 - 10 mm, you can cut a disk with a diameter of 100 mm in about an hour to facilitate work, you can use a machine tool (Fig. 2).

Frame reinforced on base 1

3. An axis 4 passes through the middle of its upper crossbar, equipped with a handle 5. A tubular drill 2 is fixed at the lower end of the axis, and a load b is fixed at the upper end. The axis of the drill can be equipped with bearings. You can make a motor drive, then you do not have to turn the handle. The machine is made of wood or metal.

Now - polishing

If you put one glass disk on top of another and, having smeared the contacting surfaces with gruel of abrasive powder with water, move the upper disk towards you and away from you, at the same time uniformly rotating both disks in opposite directions, then they will be ground to one another. The lower disc gradually becomes more and more convex, and the upper disc becomes concave. When the desired radius of curvature is reached - which is checked by the depth of the center of the recess - the arrow of curvature - they move on to finer abrasive powders (until the glass becomes dark matte). The radius of curvature is determined by the formula: X =

where y is the radius of the primary mirror; . R is the focal length.

for the first homemade telescope, the mirror diameter (2y) is chosen to be 100-120 mm; F - 1000--1200 mm. The concave surface of the upper disk will be reflective. But it still needs to be polished and coated with a reflective layer.

How to get an accurate sphere

The next step is polishing.

The instrument is still the same second glass disc. It needs to be turned into a polishing pad, and for this, a layer of resin with an admixture of rosin is applied to the surface (the mixture gives the polishing layer greater hardness).

Cook the resin for the polisher like this. Rosin is melted in a small saucepan over low heat. and then small pieces of soft resin are added to it. The mixture is stirred with a stick. It is difficult to determine the ratio of rosin and resin in advance. Having cooled a drop of the mixture well, you need to test it for hardness. If the thumbnail leaves a shallow mark with strong pressure, the hardness of the resin is close to the required one. it is impossible to bring the resin to a boil and the formation of bubbles; it will be unsuitable for work. A network of longitudinal and transverse grooves is cut on the layer of polishing compound so that the polishing agent and air circulate freely during work and the resin patches make good contact with the Mirror. Polishing is done in the same way as grinding: the mirror moves back and forth; in addition, both the polisher and the mirror are turned little by little in opposite directions. In order to obtain the most accurate sphere possible, during grinding and polishing it is very important to observe a certain rhythm of movements, uniformity in the length of the “stroke” and the turns of both glasses.

All this work is done on a simple home-made machine (Fig. 3), similar in design to a pottery one. On the basis of a thick board is placed a rotating wooden table with an axis passing through the base. A grinder or polisher is fixed on this table. So that the tree does not warp, it is impregnated with oil, paraffin or waterproof paint.

Fouquet comes to the rescue

Is it possible, without resorting to a special optical laboratory, to check how accurate the surface of the mirror turned out to be? You can, if you use a device designed about a hundred years ago by the famous French physicist Foucault. The principle of its operation is surprisingly simple, and the measurement accuracy is up to hundredths of a micrometer. The famous Soviet optician D. D. Maksutov in his youth made an excellent parabolic mirror (and it is much more difficult to obtain a parabolic surface than a sphere), using this device assembled from a kerosene lamp, a piece of cloth from a hacksaw saw and wooden blocks to test it . Here is how it works (Figure 4)

A point source of light I, for example, a puncture in a foil illuminated by a bright light bulb, is located near the center of curvature O of mirror Z. The mirror is slightly rotated so that the top of the cone of reflected rays O1 is located somewhat away from the light source itself. This vertex can be crossed by a thin flat screen H with a straight edge - the "Foucault knife". By placing the eye behind the screen near the point where the reflected rays converge, we will see that the entire mirror is, as it were, flooded with light. If the surface of the mirror is exactly spherical, then when the screen crosses the top of the cone, the entire mirror will begin to fade evenly. And a spherical surface (not a sphere) cannot - can collect all the rays at one point. Some of them will intersect in front of the screen, some - behind it. Then we see a relief shadow pattern” (Fig. 5), which can be used to find out what deviations from the sphere are on the surface of the mirror. By changing the polishing mode in a certain way, they can be eliminated.

The sensitivity of the shadow method can be judged from such experience. If you put your finger on the surface of the mirror for a few seconds and then look using a shadow device; then at the place where the finger was attached, a hillock will be visible with a rather

a noticeable shadow, gradually disappearing. The shadow device clearly showed the slightest elevation formed from the heating of a section of the mirror when it came into contact with a finger. If “Foucault's knife extinguishes the entire mirror at the same time, then its surface is indeed an exact sphere.

Several Yet important tips

When the mirror is polished and its surface is precisely brought to the desired shape, the reflective concave surface must be aluminized or silvered. The reflective aluminum layer is very durable, but it is possible to cover the mirror with it only on a special installation under vacuum. Alas, fans of such installations do not have. But you can silver the mirror at home. The only pity is that the silver fades rather quickly and the reflective layer has to be renewed.

A good main mirror for a telescope is the main one. The flat diagonal mirror in small reflecting telescopes can be replaced by a prism with total internal reflection, used, for example, in prismatic binoculars. Ordinary flat mirrors used in everyday life are not suitable for a telescope.

Eyepieces can be picked up from an old microscope or surveying instruments. In extreme cases, a single biconvex or plano-convex lens can also serve as an eyepiece.

The tube (tube) and the entire installation of the telescope can be performed in the most various options- from the simplest, where the material is cardboard, planks and wooden blocks (Fig. 6), to very perfect ones. with Details and specially cast turned on a lathe. But the main thing is the strength, stability of the pipe. Otherwise, especially at high magnifications, the image will tremble and it will be difficult to focus the eyepiece, and it is inconvenient to work with the telescope

Now the key is patience.

A schoolboy in the 7th or 8th grade can make a telescope that gives very good images at magnifications up to 150 times or more. But this work requires a lot of patience, perseverance and accuracy. But what joy and pride should one feel who gets acquainted with the cosmos with the help of the most accurate optical device - a telescope made by one's own hands!

The heaviest part for independent production is the main mirror. We recommend you a new rather simple method of its manufacture, for which there is no need for complex equipment and special machines. True, you need to strictly follow all the advice in fine grinding and especially mirror polishing. Only under this condition can you build a telescope that is in no way worse than an industrial one. It is this detail that causes the most difficulties. Therefore, we will talk about all the other details very briefly.

The blank for the main mirror is a glass disk 15-20 mm thick.

You can use a lens from the condenser of a photographic enlarger, which are often sold in shopping malls photo products. Or glue with epoxy glue from thin glass discs that are easy to cut with diamond or roller glass cutter. Make sure that the adhesive connection is minimum thickness. A "layered" mirror has some advantages over a solid one - it is not so prone to warping with temperature changes environment, and consequently, gives an image of better quality.

The grinding disc can be glass, iron or cement-concrete. The diameter of the grinding wheel should be equal to the diameter of the mirror, and its thickness should be 25-30mm. The working surface of the grinder should be glass or, even better, made of cured epoxy resin with a layer of 5-8mm. Therefore, if you managed to carve or select a suitable disk on scrap metal, or cast it from a cement mortar (1 part of cement and 3 shares of sand), then you need to arrange its working side, as shown in Figure 2.

Abrasive powders for grinding can be from carborundum, corundum, emery or from quartz sand. The latter polishes slowly, but despite all the above, the quality of the finish is noticeably higher. Abrasive grains (200-300 g will be needed) for rough grinding, when we need to make the desired radius of curvature in the mirror blank, should be 0.3-0.4 mm in size. In addition, smaller powders with grain sizes will be required.

If it is not possible to purchase ready-made powders, then it is quite possible to prepare them yourself by crushing small pieces of a grinding abrasive wheel in a mortar.

Rough polished mirror.

Fix the grinder on a stable cabinet or table with the working side up. You have to worry about the painstaking cleaning of your home sander "machine" after changing the abrasives. Why on its surface it is necessary to lay a layer of linoleum or rubber. A special pallet is very convenient, which, together with the mirror, can then be removed from the table after work. Rough grinding is done by a reliable "old-fashioned" method. Mix the abrasive with water in a ratio of 1:2. Smear on the surface of the grinder about 0.5 cm3. the resulting slurry, put the mirror blank with the outer side down and start grinding. Hold the mirror with 2 hands, this will prevent it from falling, and the correct position of the hands will quickly and accurately obtain the desired radius of curvature. Make movements during grinding (strokes) in the direction of the diameter, evenly turning the mirror and grinder.

Try from the very beginning to accustom yourself to the subsequent rhythm of work: for every 5 strokes, 1 turn the mirror in your hands by 60 °. Rate of work: approximately 100 strokes per minute. As you move the mirror back and forth across the surface of the grinder, try to keep it in a state of stable equilibrium on the circle line of the grinder. As grinding progresses, the crunch of the abrasive and the intensity of grinding decrease, the plane of the mirror and grinder become contaminated with spent abrasive and glass particles with water - sludge. It must be washed off or wiped with a damp sponge from time to time. After sanding for 30 minutes, check the indentation with a metal ruler and safety razor blades. Knowing the thickness and the number of blades that pass between the ruler and the central part of the mirror, you can easily measure the resulting recess. If it is not enough, continue grinding until you get the desired value (0.9mm in our case). If the grinding powder good quality, then rough grinding can be done in 1-2 hours.

Fine grinding.

In fine finishing, the surfaces of the mirror and grinder are rubbed against each other on a spherical surface with the highest precision. Grinding is done in several passes with increasingly fine abrasives. If during coarse grinding the center of pressure was located near the edges of the grinder, then with fine grinding it should be no more than 1/6 of the diameter of the workpiece from its center. At times it is necessary to make, as it were, erroneous movements of the mirror along the surface of the grinder, now to the left, then to the right. Start fine sanding only after a major cleaning. Large, hard particles of abrasive should not be allowed near the mirror. They have an unpleasant ability to "independently" seep into the grinding area and produce scratches. At first, use an abrasive with a particle size of 0.1-0.12 mm. The finer the abrasive, the smaller doses it should be added. Depending on the type of abrasive empirically choose its concentration with water in suspension and the value of the portion. The time of its production (suspension), as well as the frequency of cleaning from sludge. It is impossible to allow the mirror to stick (get stuck) on the grinder. It is convenient to keep the abrasive suspension in bottles, in the corks of which plastic tubes with a diameter of 2-3 mm are inserted. This will facilitate its application to the work surface and protect it from clogging with large particles.

Check the progress of grinding by viewing the mirror in the light after rinsing with water. Large knockouts left after clumsy grinding should completely disappear, the haze should be completely uniform - only in this case, work with this abrasive can be considered finished. It is useful to work for an extra 15-20 minutes, in order to grind with a guarantee not only unnoticed punches, but also a layer of microcracks. After that, rinse the mirror, grinder, pallet, table, hands and proceed to grinding with one more, smallest abrasive. Add the abrasive suspension evenly, a few drops, after shaking the bottle. If too little abrasive suspension is added, or if there are huge deviations from the spherical surface, then the mirror can "grab". Therefore, you need to put the mirror on the grinder and make the first movements very carefully, without much pressure. Particularly ticklish is the "grabbing" of the mirror in the last stages of fine grinding. If such a threat has occurred, then in no case should you rush. Take the trouble evenly (for 20 minutes) to heat the mirror with a grinder under a stream of warm water to a temperature of 50-60 °, and then cool them. Then the mirror and the grinder will "disperse". You can tap with a piece of wood on the edge of the mirror in the direction of its radius, taking all precautions. Do not forget that glass is a very fragile and low heat-conducting material and at a very large temperature difference it cracks, as sometimes happens with a glass glass if boiling water is poured into it. Quality control at the final steps of fine grinding should be carried out using a powerful magnifying glass or microscope. In the final stages of fine grinding, the likelihood of scratches increases dramatically.

Therefore, we list the precautionary measures against their appearance:
perform painstaking cleaning and washing of the mirror, pallet, hands;
do wet cleaning in the working room after each approach;
try to remove the mirror from the grinder as little as possible. It is necessary to add abrasive by moving the mirror to the side by half the diameter, evenly distributing it according to the surface of the grinder;
putting the mirror on the grinder, press it, while large particles that accidentally fall on the grinder will be crushed and will not scratch the plane of the glass blank in any way.
Separate scratches or pits will not spoil the image quality in any way. However, if there are a lot of them, then they will lower the contrast. After fine grinding, the mirror becomes translucent and perfectly reflects the rays of light falling at an angle of 15-20 °. After making sure that this is the case, sand it still in the absence of any pressure, quickly turning it to equalize the temperature from the heat of the hands. If the mirror moves simply on a thin layer of the finest abrasive, with a slight whistle resembling a whistle through the teeth, then this means that its surface is very close to spherical and differs from it only by hundredths of a micron. Our task in the future during the polishing operation is not to spoil it in any way.

Mirror polishing

The difference between mirror polishing and fine polishing is that it is produced on soft material. High-precision optical surfaces are obtained by polishing on resin polishing pads. Moreover, the harder the resin and the smaller its layer on the surface of a hard grinder (it is used as the base of the polishing pad), the more accurate the surface of the sphere on the mirror is. To make a resin polishing pad, you first need to prepare a bitumen-rosin mixture in solvents. To do this, grind into small pieces 20 g of grade IV oil-bitumen and 30 g of rosin, mix them and pour into a bottle with a capacity of 100 cm3; then pour 30 ml of gasoline and 30 ml of acetone into it and close the cork. To speed up the dissolution of rosin and bitumen, periodically shake the mixture, and after a few hours the varnish will be ready. Apply a layer of varnish to the surface of the grinder and let it dry. The thickness of this layer after drying should be 0.2-0.3 mm. After that, pick up the varnish with a pipette and drip one drop onto the dried layer, preventing the drops from merging. What is very important is to evenly distribute the drops. After the varnish has dried, the polisher is ready for use.

Then prepare a polishing suspension - a mixture of polishing powder with water in a ratio of 1:3 or 1:4. It is also convenient to store it in a bottle with a stopper, equipped with a polyethylene tube. Now you have everything to polish the mirror. Moisten the surface of the mirror with water and put a few drops of polishing suspension on it. Then carefully place the mirror on the polishing pad and move it around. The movements for polishing are the same as for fine grinding. But you can press on the mirror only when it moves forward (shift from the polishing pad), it is necessary to return it to its original position without any pressure, holding its cylindrical part with your fingers. Polishing will go almost without noise. If the room is quiet, you can hear a noise that resembles breathing. Polish slowly, without pressing too hard on the mirror. It is important to set a mode in which the mirror under load (3-4 kg) goes forward rather tightly, and back easily. The polisher seems to "get used" to this mode. The number of strokes is 80-100 per minute. Make the wrong moves from time to time. Check the condition of the polisher. Its pattern should be uniform. If necessary, dry it and drip varnish in the right places, after thoroughly shaking the bottle with it. The polishing process should be monitored in the light, using a strong magnifying glass or a microscope with a magnification of 50-60 times.

The surface of the mirror should be polished evenly. It is very bad if the middle zone of the mirror or near the edges is polished faster. This can happen if the pad surface is not spherical. This defect must be immediately eliminated by adding bitumen-rosin varnish to the lowered places. After 3-4 hours, the work usually comes to an end. If you examine the edges of the mirror through a strong magnifying glass or microscope, then you will no longer see pits and small scratches. It is useful to work for another 20-30 minutes, reducing the pressure by two to three times and making stops for 2-3 minutes every 5 minutes of work. This ensures that the temperature equalizes from the heat of friction and hands and that the mirror acquires a more precise shape of a spherical surface. So, the mirror is ready. Now oh design features and details of the telescope. The views of the telescope are shown in the sketches. You will need few materials, and they are all available and relatively cheap. As a secondary mirror, you can use a total internal reflection prism from a large binocular, a lens or a light filter from a camera, on the flat surfaces of which a reflective coating is applied. As a telescope eyepiece, you can use an eyepiece from a microscope, a short-focus lens from a camera, or single plano-convex lenses with a focal length of 5 to 20 mm. It should be especially noted that the frames of the primary and secondary mirrors must be made very carefully.

The quality of the image depends on their correct adjustment. The mirror in the frame should be fixed with a small gap. The mirror must not be clamped in the radial or axial direction. In order for the telescope to provide a high quality image, it is necessary that its optical axis coincides with the direction to the object of observation. This adjustment is made by changing the position of the secondary auxiliary mirror, and then adjusting the nuts of the main mirror frame. When the telescope is assembled, it is necessary to make reflective coatings on the working surfaces of the mirrors and install them. The easiest way is to cover the mirror with silver. This coating reflects more than 90% of the light, but fades over time. If you master the method of chemical deposition of silver and take measures against tarnishing, then for most amateur astronomers this will be the best solution to the problem.

The problem of using solar energy has occupied the best minds of mankind since ancient times. It was clear that the Sun is the most powerful source of free energy, but no one understood how to use this energy. If you believe the ancient writers Plutarch and Polybius, then the first person to practically use solar energy was Archimedes, who, using some optical devices he invented, managed to collect the sun's rays into a powerful beam and burn the Roman fleet.

In essence, the device invented by the great Greek was the first concentrator of solar radiation, which collected the sun's rays into one energy beam. And at the focus of this concentrator, the temperature could reach 300 ° C - 400 ° C, which is quite enough to ignite the wooden ships of the Roman fleet. One can only guess what kind of device Archimedes invented, although, according to modern ideas He had only two options.

The very name of the device - a solar concentrator - speaks for itself. This device receives the sun's rays and collects them into a single energy beam. The simplest concentrator is familiar to everyone from childhood. This is an ordinary biconvex lens, which could burn out various figures, inscriptions, even entire pictures, when the sun's rays were collected by such a lens into a small dot on a wooden board, a sheet of paper.

This lens belongs to the so-called refractor concentrators. In addition to convex lenses, Fresnel lenses and prisms also belong to this class of concentrators. Long-focus concentrators based on linear Fresnel lenses, despite their low cost, are used very little in practice, since they are large. Their use is justified where the dimensions of the concentrator are not critical.

Refractory Solar Concentrator

The prismatic concentrator of solar radiation is deprived of this shortcoming. Moreover, such a device is also capable of concentrating part of the diffuse radiation, which significantly increases the power of the light beam. The trihedral prism, on the basis of which such a concentrator is built, is both a radiation receiver and a source of an energy beam. In this case, the front face of the prism receives radiation, the back face reflects, and radiation is already emerging from the side face. The operation of such a device is based on the principle of total internal reflection of rays before they hit the side face of the prism.

Unlike refractor concentrators, reflex concentrators work on the principle of collecting reflected sunlight into an energy beam. According to their design, they are divided into flat, parabolic and parabolic-cylindrical concentrators. If we talk about the effectiveness of each of these types, then the highest degree concentrations - up to 10,000 - give parabolic concentrators. But to build systems solar heating mainly flat or parabolic-cylindrical systems are used.

Parabolic (reflector) solar concentrators

Practical application of solar concentrators

Actually, the main task of any solar concentrator is to collect the radiation of the sun into a single energy beam. And you can use this energy in various ways. It is possible to heat water with free energy, and the amount of heated water will be determined by the size and design of the concentrator. Small parabolic devices can be used as a solar cooker.

Parabolic concentrator as a solar oven

You can use them for additional lighting of solar panels to increase the power output. And it can be used as an external heat source for Stirling engines. The parabolic concentrator provides a focus temperature of about 300°C - 400°C. If the focus of such a relatively small mirror put, for example, a stand for a kettle, a frying pan, you get a solar oven, on which you can cook food very quickly, boil water. A heater with a heat carrier placed at the focus will quickly heat up even running water, which can then be used for household purposes, for example, for showering, washing dishes.

The simplest scheme for heating water with a solar concentrator

If a Stirling engine of suitable power is placed at the focus of a parabolic mirror, then a small thermal power plant can be obtained. For example, Qnergy has developed and launched the QB-3500 Stirling engines, which are designed to work with solar concentrators. In fact, it would be more correct to call them generators of electric current based on Stirling engines. This unit produces electricity power of 3500 watts. The output of the inverter is a standard voltage of 220 volts 50 hertz. This is quite enough to provide electricity to a house for a family of 4, a dacha.

By the way, using the principle of operation of Stirling engines, many craftsmen make devices with their own hands that use rotational or reciprocating motion. For example, water pumps for summer cottages.

The main disadvantage of a parabolic concentrator is that it must be constantly oriented towards the sun. Industrial helium plants use special tracking systems that rotate mirrors or refractors to follow the movement of the sun, thereby ensuring reception and concentration maximum number solar energy. For individual use, it would hardly be advisable to use such tracking devices, since their cost can significantly exceed the cost of a simple reflector on a conventional tripod.

How to make your own solar concentrator

The easiest way to make a homemade solar concentrator is to use an old plate from satellite dish. First you need to decide for what purposes this hub will be used, and then, based on this, choose the installation site and prepare the base and fasteners accordingly. Thoroughly wash the antenna, dry it, stick a mirror film on the receiving side of the dish.

In order for the film to lie flat, without wrinkles and folds, it should be cut into strips no more than 3-5 centimeters wide. If you intend to use the concentrator as a solar oven, it is recommended to cut a hole in the center of the dish with a diameter of about 5 - 7 centimeters. Through this hole, a bracket with a support for dishes (burner) will be passed. This will ensure the immobility of the container with the cooked food when the reflector is turned to the sun.

If the plate is small in diameter, it is also recommended to cut the strips into pieces about 10 cm long. Stick each piece separately, carefully adjusting the joints. When the reflector is ready, it should be installed on the support. After that, you will need to determine the focus point, since the optical focus point at the satellite dish does not always coincide with the position of the receiving head.

Homemade solar concentrator - oven

To determine the focal point, you need to arm yourself with dark glasses, a wooden plank and thick gloves. Then you need to direct the mirror directly at the sun, catch a sunbeam on the board and, bringing the board closer or further away from the mirror, find the point where this sunbeam will have the minimum size - a small point. Gloves are needed in order to protect your hands from burns if they accidentally fall into the beam area. Well, when the focus point is found, it remains only to fix it and mount the necessary equipment.

Options self-manufacturing there are many solar concentrators. In the same way, you can make a Stirling engine from improvised materials yourself. And you can use this engine for a variety of purposes. How much imagination, desire and patience is enough.