Homemade solar concentrator made of 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 a beam of reflected rays through the eyepiece to the observer. The element marked with the number 3 is the eyepiece 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 the rays reflected by the mirror.

An ordinary household flat mirror is not always suitable for use as a diagonal mirror in a homemade telescope - a telescope needs an optically more accurate surface. Therefore, as a diagonal mirror, you can use the flat surface of a plano-concave or plano-curved optical lens, if you first cover this plane 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 a cone of rays that are reflected by the main mirror. When the mirror is rectangular or elliptical, the sides or axes relate to each other as 1: 1.4.

The lens and eyepiece of a homemade reflector telescope are mounted in the telescope tube mutually perpendicularly. To mount the main mirror of a homemade telescope, you need a frame, wood or metal.

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 tube.

Three layers of thick cardboard should be glued together with wood or casein glue, then insert the cardboard tube into the metal stiffening rings. A bowl for the rim of the main mirror of a homemade telescope and a pipe cover are also made of metal.

The length of the tube (tube) of a homemade reflector telescope should be equal to the focal length of the main mirror, and the inner diameter of the tube should be 1.25 times the diameter of the main mirror. From the inside, the tube of a self-made reflector telescope should be "blackened", ie. paste over with matte black paper or paint with black matte paint.

A homemade reflector telescope must be installed on a special stand - a mount before use.

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 it is more than 900 mm, then it is better to make the surface of the mirror 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 and a thickness of at least 8-10 mm, with a diameter of 120 mm - about 12-14 mm) made of well-annealed glass, for example, mirror, display, and porthole glass. If you have 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. Drill wall thickness - 1-2 mm.

Grind discs on a machine. On a thick board - the base - a revolving round or six-octagonal table is fixed. An axle is firmly fixed in its center, rotating at the base. 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 rough grinding process, ring grinding is used in modern amateur practice. For a ring, take a piece of thick-walled cast iron pipe... The diameter of the ring is approximately half the diameter of the mirror. Putting the future mirror in place of the grinder, grind it with a ring, lubricating the gruel from an abrasive with water. Make sure that the ring does not extend beyond the edge of the sander. The ring and machine table must rotate evenly in opposite directions at all times. When sanding with a ring, a depression in the glass is obtained much faster than when sanding glass with glass. For further grinding, in addition to a 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 wood impregnated with a water-repellent composition is also used. Squares of glass or plexiglass are glued to the base of such a grinder. Special metal polishing tools are also used.

Their bases, which look like a sphere, are turned on a lathe. The use of the grinders described above allows you to limit yourself to one glass disc - the future mirror.

When approaching or moving away from the mirror, ensure that the artificial star fills the entire surface of the mirror with its light. If now slowly cross the top of the cone of rays with the "Foucault knife", then the entire mirror will "go out" simultaneously. This means that all the rays reflected from the mirror converge at one point. If the curvature of the surface of the mirror 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 mirror movements (strokes) or the shape of the polishing pad. The actual deviations of the surface of your mirror from the sphere are measured in fractions of a micron.

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

In a Newtonian reflector telescope, a diagonal flat mirror deflects sideways a cone of rays reflected from the main mirror. It is very difficult to make a good flat mirror yourself. Use a total internal reflection prism from prismatic binoculars instead of this mirror. For the 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.

You can also use a flat lens surface, a camera filter surface, or any other optically accurate plane as a flat diagonal mirror. Cover it with a layer of silver or aluminize.

How to build a solar water heater. It would be 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 N latitude.

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

Parabolic antenna.

Any antenna can be used - iron, plastic or fiberglass. The antenna should be panel type, not mesh antenna. Antenna area and shape are important here. Remember, heating power = antenna surface area. 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. The glue with which the film will stick to the parabola.

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

Step 1 Redesigning the focusing antenna solar radiation instead of radio waves.

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

This is almost as easy as it sounds. You just need to take into account that if the antenna, for example, is 2.5 m in diameter, and the film is 1 m wide, then you do not need 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 in small strips and attach it to the antenna with glue. Make sure the antenna is clean before applying tape. If there are areas where the paint is swollen, clean them with sandpaper. You need to align all the irregularities. Please note that the LNB is removed from its place, otherwise it may melt. After gluing the film and installing the antenna in place, keep your hands or face away from the head mount - you risk getting serious sunburn.

Step 2 tracking system.

As stated above - the author bought a tracking system on Ebay. You can also look for rotary sun tracking systems. But I found a simple, penny-priced circuit that tracks the position of the sun fairly 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.

Who cares the photo is taken from here:

Step 3 Create a heat exchanger-collector

To make a heat exchanger, you need a copper tube rolled into a ring and placed in the focus of our concentrator. But first we need to know the size of the focal point of the dish. To do this, remove the LNB converter from the plate, leaving the converter mounting racks. Now you need to turn the plate in the sun, after fixing a piece of 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, turn the antenna away 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 put your hand into the focus of the mirror - this is dangerous, you can get severely burned. Let it cool down. Measure the size of the burned 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, this one in the photo above. His wife gave me a birthday present. It was a rather spontaneous gift like this: “I don’t know what to give you, oh look at the store, let's go and see”. In principle, I was very happy with such a gift, the thing is very interesting. However, during the time of using it, I realized that I want more. This PowerSeeker 127EQ telescope has a number of essential design flaws which I simply did not know about due to inexperience. The main disadvantage is the spherical main mirror and the corrective lens to it. As a result, an overcomplicated optical design, inaccuracies in the fit of the corrective lens, which is also 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 needed 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 do it yourself? The answer is not really obvious. It's probably easier to buy, or maybe cheaper? Build yourself in the absence of experience is a difficult technical task, it is not known whether it will work out at all and it is not clear whether it will be cheaper than just buying.

I entered the slippery path of self-telescoping. Next, I will tell you about my first steps in this direction, but I immediately warn you that do not wait to read the article with a happy ending just yet. I am very far from him (if he happens at all).

So, you need to start by studying the theory.

In my opinion, there is nothing better than the book "Telescopes for Astronomy Amateurs", L.L.Sikoruk, 1982. Despite the fact that the book is more than thirty years old, I have not seen a more detailed exposition "inside and out". There is also a book by M. S. Navashin "Telescope of an amateur astronomer", 1979. Also useful.

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

The last shelter: youtube.com. It may seem strange, but telescopes around the world are built by many people. Some even video blogs and show the manufacturing process. YouTube keywords: 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 certain). In Europe and America there are special shops that sell mirror blanks, grinding powders, and tools and kits for making mirrors (teleskope mirror kit).

We are now, of course, not 79 or 82 years old, but where to get the blank for the telescope mirror? Or where to get grinding powders? 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 disc with a diameter of 200 millimeters and I was told that it would cost about thirty thousand without shipping. Perhaps there is a very high quality optical glass, but I just do not understand it as an amateur (without irony, I know that somewhere exceptional quality may be required).

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

In general, I decided to make from scrap materials, as Sikoruk advised to do in his book. The material at hand is display glass (but not heated). I need to cut several discs from glass with a thickness of 10 millimeters and then glue them liquid glass... In his book, Sikoruk writes and substantiates the required thickness of the main mirror, depending on its diameter.

The first epic. Cutting a workpiece from glass

I went to a glazier and asked him to cut out rectangular pieces of 10 mm glass for me, about 250x250 mm, but they should all be from the same sheet to be sure of the same properties of all blanks.

I went to the store and bought a pair of aluminum pans with an inner 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 are doing 180 right away.

The pan was sawn and a weight and two protruding bolts were bolted to the bottom.

This will be the cutter.

Next comes the long and painful process of making a machine for cutting a workpiece. The engine from the old one will come in handy here. washing machine, a pulley from it, some old gearbox, pieces of plywood, studs, nuts and other nonsense.
In general, it looks like this:

The lid of the pan is glued to the glass with silicone and its edges are roughened up. It serves as a centering element for my cutter. The milling cutter, that is, half the pan is put on from above and rotated by a gearbox from the motor.

This thing works like this (my video):

During work, you need to constantly add abrasive under the edges of the cutter. I worked with the abrasive for five to seven minutes, the abrasive escaped and mixed with crumbs of glass and aluminum. Wash off the old abrasive and add a new one. Then I got used to doing all this on the fly without turning off the engine. It worked, washed it off and immediately 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 days of mammoths. I had a piece of old grinding wheel... I crushed it with a hammer on an anvil.

The resulting pieces were still knocked 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 permissible, but further it will be necessary to improve the culture of production.

As a result, one 180 mm disc out of a 10 mm sheet on my machine is cut out in about three to three and a half hours. I cut 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 Sikoruk advises, and I will have two 180 mm blanks for the main mirror. Then I'll start sharpening them and probably ruin one. Well, the second one, I will hope that it will work out.

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 shaping, grinding, grinding and then polishing. I'm honestly stuck at this point. Here are some illustrations from Telescopes for Astronomy Lovers:

Roughing:

Grinding:

Typical mistakes:

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

This is how Sikoruk writes in his book:

The process of figuring and shadow testing is difficult to separate into its components - it 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, is often in no hurry to finish, trying to work this way and that, finding great pleasure in the process of figuring, although, no doubt, the sight 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 by the fact that the master himself often wants a little mysticism, when figurativeness ceases to be just a technology, but becomes largely art. No wonder D. D. Maksutov said that the optician prefers to "conjure" over the homemade resin of the polishing pad, not trusting the factory resin. (However, if you have the opportunity to purchase factory polishing resin, you must 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 reasons that clearly lead to trouble.

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

I've watched a lot of YouTube video demos: there is both shaping and polishing and the so-called "parabolization" with the magic "W" stroke.

Here are some colorful videos:
Rough processing:

Mirror grinding: 200 f / 5 fine grinding:

People also build machines for mechanical processing mirrors:

From all this, it turns out that everyone does, how they come up with it, but how to do it in order to guarantee the result? There is something to think about ...

After rather long deliberation, I decided before sharpening to try to make a software model of the entire grinding process. For some reason, it seemed to me that it would be quite simple to do this. I thought that I would make a grinding machine, something like the last video.

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

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

This video is generated from snapshots of the virtual stripping process in my program:

I thought that by choosing the stroke length, the length of the arms of the crank mechanism (and its movement is far from a sinusoid) in the program model, 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 realize 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 surface of the workpiece also changes.

When I was writing this article, I even thought here to cite 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 intend to make a software model of the process of figuring the mirror. Perhaps, if I succeed, I will publish my code.

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

Why 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 doing it. A situation may occur that you purchase an expensive telescope, and the science of the Universe will disappoint you, or you simply realize that this is not your business at all. In order to figure out what's what, it is enough to make a telescope for an amateur. Observing the sky through such a device will allow you to see many times more than through binoculars, and you can also figure out if this activity is interesting to 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 make it possible to clearly see the lunar craters. With it, you can see Jupiter and even make out four of its main moons. The rings of Saturn familiar to us from the pages of textbooks can also be seen with a telescope made with our own hands.

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 distant objects can be seen, as well as the magnification of the device, depends on the diameter of the objective. The second member of the tandem, the eyepiece, is designed to enlarge the resulting image so that our eyes 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 mirrored lens. Lenses for a telescope, unlike a reflective mirror, can be found quite easily in specialized stores. Buying a mirror for a reflector will not be cheap, and making it yourself will be impracticable for many.

Therefore, as it has already become clear, we will be assembling a refractor, and not a mirror telescope. Let us end the theoretical excursion with the concept of telescope magnification. It is equal to the ratio of the focal lengths of the lens and 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 workpieces will be about seventy millimeters. It should also be noted that it is better not to choose spectacle lenses for a telescope, since they generally have a concave-convex shape and are poorly suited for a telescope, although if they are at hand, then you can use them. It is recommended to use long focal biconvex lenses. As an eyepiece, you can take an ordinary magnifier of thirty millimeters in diameter. If it is possible to reach the eyepiece from the microscope, then undoubtedly it is worth taking advantage of it. It works great for a telescope too. So what to make a body for our future optical assistant? Two pipes are perfect different diameters made of 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 ultimately be an eyepiece assembly, and it is recommended to make the main one a meter long. If you don't find the necessary blanks at hand, it doesn't matter, the case can be made from an unnecessary roll of wallpaper. For 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 what kind of lens we are using. Telescope stand Very important point in creating your own telescope - preparing a special support for it. Without one, it will be almost impossible to use it. There is an option for installing the telescope on a tripod from a camera, which is equipped with a moving head, as well as fasteners that will allow you to fix various positions of the body. Telescope Assembly The objective lens is mounted in a small tube with the bulge outward. It is recommended to fasten it with the help of a frame, which is a ring similar in diameter to the lens itself.

You have a wonderful master mirror blank. But only if these are lenses from K8. Because condensers (which are undoubtedly condenser lenses) often include a pair of lenses, one of which is from the crown, the other from the 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 perfect as a base for a polishing pad, but it will not work with it, since a flint has a much higher hardness and grindability than a crown. In this case, use a plastic grinder.

Secondly, I strongly advise you to carefully read not only Sikoruk's book, but also the "Telescope of an amateur astronomer" by MS. Navashin. And in terms of tests and measurements of the mirror, you should focus on Navashin, who has this aspect in great detail. Naturally, it is not worth making exactly a shadow device "according to Navashin", since now it is easy to make improvements to its design, such 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 will also allow close the "star" to the knife, it is advisable to use the rail from the optical bench as a base, etc.). The manufacture of a shadow device must be approached with all attention, since the quality of your mirror will be determined by how well you make it.

In addition to the aforementioned rail from the optical bench, a useful "swag" for its manufacture is the caliper from the lathe, which will become a wonderful device for smoothly moving the Foucault knife and at the same time measuring this movement. An equally useful find will be a ready-made slit from a monochromator or diffractometer. I also advise you to adapt a webcam to a shadow device - this will eliminate the error from the position of the eye, reduce convection interference from the heat of your body, 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 attachment of all parts must be perfectly rigid and durable, and the movement must be free of play. Organize a pipe or tunnel along the entire path of the beams - this will reduce the effect of convection currents, and in addition, will allow you to work with light. In general, convection currents are the scourge of any mirror testing method. Fight them with all possible means.

Invest in some good abrasives and resins. Cooking resin and eluting abrasives is, firstly, a waste of energy, and secondly, a bad resin is a bad mirror, and bad abrasives are a bunch 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. A wooden barrel filled with rubble is absolutely ideal here, around which Chikin, Maksutov and other "founding fathers" once walked. A useful addition to Chikin's barrel is the "Grace" disc, which allows you not to wind kilometers around the barrel, but to work while standing in one place. It is better to equip a barrel for roughing and rough grinding on the street, but fine grinding and polishing is already a matter for a room with a constant temperature and without drafts. An alternative to a barrel, especially at the fine sanding stage and when polishing, is the floor. On the knees, of course, it is less convenient to work, but the rigidity of such a "machine" is ideal.

Necessary Special attention to give the fastening of the workpiece. A good option for unloading the lens is to stick it behind a "patch" of minimum size in the center and three stops near the edges, which should only touch, but not press on the workpiece. Piglet needs to be found on the 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 roughing and bring it to a fine grinding. The width of the chamfer should be calculated so that it is preserved 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.

Roughing with a ring or a reduced grinder in the "mirror from below" position is the most rational, but given the small size of the mirror, you can also do according to Navashin - a mirror from above, a grinder of normal size. Silicon carbide or boron carbide is used as an abrasive. When stripping, one must be careful not to find astigmatism and "leave" in 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 closer to the end of the roughing. If, during roughing, the surface as close as possible to the sphere was initially obtained, this will sharply accelerate all further work on grinding.

Abrasives for grinding - starting from the 120th number and finer, it is better to use aluminum oxide, and larger - carborundum. The main characteristic of abrasives, to which one must strive, is the narrowness of the particle distribution spectrum. If the particles in a given abrasive number vary in size, then the larger grains are the source of scratches, and the smaller ones 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 thinner 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 stages are enough short. Why it works - I don't know. With a good abrasive, you can grind after the 220th number immediately with a thirty-micron one. It is good to add "Fairy" 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 and 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 thin) is to polish the surface by rubbing with suede with polyrite to a shine, after which you can easily determine the focal point by the Sun or a lamp and even (at more subtle stages of grinding) get shadow picture. A sign of the spherical shape accuracy is also the uniformity of the ground surface and fast uniform grinding of the entire surface after changing the abrasive. Vary the stroke length within small limits - this will help to avoid a "broken" surface.

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

Directly behind the lens, further along the pipe, it is necessary to equip a diaphragm in the form of a disc with a thirty-millimeter hole strictly in the middle. The diaphragm is designed to cancel out image distortions caused by the use of a single lens. Also, setting it will affect the amount of light that the lens receives. The telescope lens itself is mounted near the main tube. Naturally, the eyepiece itself is indispensable in the eyepiece assembly. First you need to prepare fasteners for it. They are made in the form of a cardboard cylinder and are similar in diameter to an eyepiece. The mount is installed inside the pipe using two discs. They are the same diameter as the cylinder and have holes in the middle. Setting up the unit at home Focus the image using the distance from the lens to the eyepiece. For this, the eyepiece assembly is moved 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 perform 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 objective with the eyepiece is parallel and their centers are on the same straight line. Another way to make a DIY telescope is to change the size of the aperture. By varying its diameter, you can achieve an optimal picture. Using optical lenses of 0.6 diopters, which have a focal length of about two meters, it is possible to increase the aperture and make the approximation on our telescope much larger, but it should be understood that the body will also increase in this case.

Caution - 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, with a telescope at their disposal, many will want to take a closer look. But you need to know that this is very dangerous. After all, sunlight, passing through the optical systems we have built, can focus 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, we must remember very much important rule: you cannot look at the Sun through approaching devices, especially through 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. Place a diaphragm with a hole about 30 mm in diameter between them. This is a last resort. But it is better to use a long focal biconvex lens.

For the eyepiece, you can take an ordinary magnifying glass (loupe) 5-10 times with a small diameter of about 30 mm. An eyepiece from a microscope can also be used as an option. 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, eyepiece assembly) is inserted into a long tube (about 1 m, main). The inner diameter of the main tube must 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 lens diameter and about 10 mm thick). 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 installed closer to the edge of the main tube. The eyepiece is installed in the eyepiece assembly closer to its edge. To do this, you will need to make an eyepiece holder out of cardboard. It will consist of a cylinder equal in diameter to the eyepiece. This cylinder will be attached to inside tubes with two discs with a diameter equal to the inner diameter of the eyepiece assembly with a hole equal to the diameter of the eyepiece.

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

When creating a telescope, it must be borne in mind that the lens and eyepiece must be parallel to each other, and their centers must be strictly on the same line.

Making a homemade reflector telescope

There are several reflector telescope systems. It is easier for the amateur astronomer to make a reflector of the Newtonian system.

As mirrors, you can use plano-convex condenser lenses for enlargers, 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 incident light. Therefore, it must be coated with a reflective layer of aluminum or silver. It is impossible to aluminize a mirror at home, but silver is quite possible.

In a Newtonian reflector telescope, a diagonal flat mirror deflects sideways a 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 a layer of silver.

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

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

For a reflector telescope, make a parallax tripod with a polar axis and a declination axis. The polar axis should point to the North Star.

Such means are considered to be light filters and a method of projecting an image onto a screen. What if you didn't manage to assemble the 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 you should not despair. You can find a telescope in the store for a reasonable price. The question immediately arises: "Where are they sold?" This technique can be found in specialized astrodevice stores. If this is not the case in your city, then it is worth visiting a photographic equipment store or finding another store that sells 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 see the telescope overview before the hike. First, you will understand the characteristics of optical devices. Secondly, it will be more difficult to deceive you and slip a low-quality product.

Then you will definitely not be disappointed with the purchase. A few words about buying a telescope through the World Wide Web. This type of shopping is becoming very popular nowadays, and it is possible that you will use it. It is very convenient: you are looking for the device you need, and then you order. However, you can stumble upon such a nuisance: after a long choice, it may turn out that the product is no longer in stock. A much more annoying problem is the delivery of the goods. It's no secret that a telescope is a very fragile thing, so only fragments can be delivered to you. The option of buying a telescope from hand is possible.

This option will allow you to save a lot, but you should be well prepared so as not to buy a broken item. Astronomers' forums are a good place to find a potential salesperson. Price for a telescope Let's consider some price categories: About five thousand rubles. Such a device will correspond to the characteristics of a home-made telescope. Up to ten thousand rubles. This unit 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. Professional and semi-professional telescopes fall into this category.

Home-made reflector telescopes are built by amateurs of astronomy, mainly according to Newton's system. It was Isaac Newton who first created a reflector telescope in about 1670. This allowed him to get rid of chromatic aberrations (they lead to a decrease in the clarity of the image, to the appearance on it of colored contours or stripes, which are not present on a real object) - the main disadvantage of the refractor telescopes that existed at that time.

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

The diagonal mirror is manufactured in small dimensions, it is flat and can have a rectangular or elliptical shape. A diagonal mirror is installed on the optical axis of the main mirror (lens), 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 - a telescope needs an optically more accurate surface. Therefore, as a diagonal mirror, you can use the flat surface of a plano-concave or plano-curved optical lens, if you first cover this plane 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 a cone of rays that are reflected by the main mirror. When the mirror is rectangular or elliptical, the sides or axes relate to each other as 1: 1.4.

The lens and eyepiece of a homemade reflector telescope are mounted in the telescope tube mutually perpendicularly. To mount the main mirror of a homemade telescope, you need a frame, wood or metal.

To make a wooden frame for the main mirror of a homemade reflector telescope, you can take a round or octagonal plate with a thickness of at least 10 mm and 15-20 mm larger than the diameter of the main mirror. The main mirror is fixed on this plate with 4 pieces of thick-walled rubber tube, which are put on the 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 tube.

Three layers of thick cardboard should be glued together with wood or casein glue, then insert the cardboard tube into the metal stiffening rings. A bowl for the rim of the main mirror of a homemade telescope and a pipe cover are also made of metal.

The length of the tube (tube) of a homemade reflector telescope should be equal to the focal length of the main mirror, and the inner diameter of the tube should be 1.25 times the diameter of the main mirror. From the inside, the tube of a self-made reflector telescope should be "blackened", ie. paste over with matte black paper or paint with black matte paint.

The eyepiece assembly of a homemade reflector telescope in its simplest design can be based, as they say, "on friction": a movable inner tube moves along a fixed outer tube, providing the necessary focusing. The eyepiece assembly can also be threaded.

A homemade reflector telescope must be installed on a special stand - a mount before use. You can purchase a ready-made factory mount, or make it yourself, from scrap materials. You can read more about the types of mounts for homemade telescopes in our next materials.

Surely a newcomer will not need a mirror apparatus with astronomical cost. This 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 our own hands, and some of the nuances of buying a new apparatus for observing the stars. In addition to the method that we have considered, there are others, but this is already a topic for another article. Whether you have assembled your telescope at home or purchased a new one, astronomy will allow you to immerse yourself in an unknown world and get an experience that you have never experienced before.

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

all four surfaces are coaxial. It is almost impossible to make such a lens in an amateur environment. It is difficult to get a good, even small, lens for a telescope.

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

Beams of light are emitted from the observed object (Fig. 1). The main concave (in the simplest case - spherical) mirror 1, collecting 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 block the open end of the telescope tube 4 with his head. On the side of the tube opposite the diagonal flat mirror a hole is cut for the exit of the cone of beams and the eyepiece tube 5 is reinforced. that the reflecting surface is processed with a 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 accessible to the student.

First, cut out the main mirror.

The main concave mirror can be made from ordinary mirrored, table or display glass. It must be of sufficient thickness and well annealed. Poorly annealed glass strongly warps 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 be more than 100 mm. A slurry of emery powder or carborundum with water is applied under a piece of metal pipe of a suitable diameter with a wall thickness of 02-2 mm. Two discs are cut from the mirror glass. A disc with a diameter of 100 mm can be cut by hand from glass with a thickness of 8 - 10 mm in about an hour. To facilitate the work, you can use a machine tool (Fig. 2).

The frame is reinforced on the base 1

3. Axle 4, equipped with a handle, passes through the middle of its upper crossbar. At the lower end of the axis, a tubular drill 2 is fixed, and on the upper end, a load b. The drill axis can be fitted with bearings. You can make a motor drive, then you don't have to turn the handle. The machine is made of wood or metal.

Now - grinding

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

where y is the radius of the main mirror; ... P is the focal length.

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

How to get an exact sphere

The next step is polishing.

The instrument is 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).

Boil the resin for the polishing pad like this. In a small saucepan, the rosin is melted 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 in advance the ratio of rosin to resin. Having well cooled a drop of the mixture, you need to test it for hardness. If the thumbnail leaves a shallow mark under strong pressure, the hardness of the resin is close to the required one. bring the resin to a boil and no bubbles will form; it will be unusable. A network of longitudinal and transverse grooves is cut into the layer of polishing compound to allow the polishing agent and air to circulate freely during operation and the resin areas to give good contact with the Mirror. Polishing is done in the same way as grinding: the mirror moves back and forth; in addition, both the polishing pad and the mirror turn slightly in opposite directions. In order to obtain the most precise 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 rotation of both glasses.

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

Fouquet's device comes to the rescue

Is it possible, without going to a special optical laboratory, to check how accurate the mirror surface is? 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 Microyaa. The famous Soviet optician D. D. Maksutov in his youth made an excellent parabolic mirror (and a parabolic surface is much more difficult to obtain than a sphere), using this device, assembled from a kerosene lamp, a piece of cloth from a hacksaw and wooden blocks, to test it ... This is how it works (fig. 4)

A point light source I, for example, a puncture in the foil illuminated by a bright lamp, is located near the center of curvature O of mirror Z. The mirror is slightly turned 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 rectilinear edge - "Foucault's 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 extinguish evenly. And a spherical surface (not a sphere) cannot - can collect all the rays at one point. Some of them will cross in front of the screen, some - behind it. Then we see a relief shadow pattern ”(Fig. 5), by which one can 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 this 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 applied, a bump will be visible with a rather

a noticeable shadow that gradually disappears. The shade device clearly showed an insignificant elevation formed from the heating of a section of the mirror in contact with a finger. If “Foucault's knife extinguishes the entire mirror at the same time, then its surface is a really precise sphere.

Several Yet important tips

When the mirror is polished and its surface is precisely shaped to the desired shape, the reflective concave surface needs to be aluminized or silver-plated. The reflective layer of aluminum is very durable, but it can only be coated with a mirror in a special installation under vacuum. Alas, amateurs do not have such installations. But you can also use a silver mirror at home. The only pity is that the silver tarnishes rather quickly and the reflective layer has to be renewed.

A good main mirror for a telescope is the main one. A 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 different options- from the simplest, where the material is cardboard, planks and wooden blocks (Fig. 6), to very perfect. with Parts and specially cast turned on a lathe. But the main thing is the strength and stability of the pipe. Otherwise, especially at high magnifications, the image will shake and it will be difficult to focus the eyepiece, and it will be inconvenient to work with the telescope.

Now the key is patience

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

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

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

You can use a lens from a condenser photomagnifier, which are often sold in shopping centers photographic goods. Or glue with epoxy glue from glass thin discs, which are easy to cut with diamond or roller glass cutter... Take the trouble to keep the adhesive bond minimum thickness... A "layered" mirror has some advantages over a solid one - it is not so susceptible to warping with changes in temperature the environment, and consequently, gives a better quality image.

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 sander should be glass or, even better, cured epoxy with a layer of 5-8mm. Therefore, if you managed to carve or select a suitable disk on scrap metal, or cast it from cement mortar (1 part of cement and 3 parts of sand), then you need to arrange its working side, as shown in Figure 2.

Abrasive powders for grinding can be of carborundum, corundum, emery, or 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 required 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 the powders in finished form, then it is quite possible to prepare them yourself by crumbling small pieces of a grinding abrasive wheel in a mortar.

Rough grinding of the mirror.

Attach the sander to a stable stand or table, with the working side up. You should take care of the painstaking cleaning of your home sander after replacing the abrasives. Why should a layer of linoleum or rubber be laid on its surface. A special pallet is quite convenient, which, together with a mirror, can then be removed from the table after work. Rough grinding is done using a reliable "old-fashioned" method. Mix the abrasive with water in a 1: 2 ratio. Smear on the surface of the sander about 0.5 cm cube. the resulting gruel, put the mirror blank with the outside down and start sanding. Hold the mirror with 2 hands, this will protect it from falling, and the correct position of the hands will give you a quick and accurate obtaining of the desired radius of curvature. Make the movements during grinding (strokes) in the direction of the diameter, evenly twisting the mirror and the grinder.

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

Fine grinding.

With fine finishing, the surfaces of the mirror and the grinder are rubbed against each other with the highest precision on a spherical surface. Grinding is done in several rounds with finer and finer abrasives. If, during coarse grinding, the center of pressure was located close to 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 over the surface of the grinder, then to the left, then to the right. Start fine sanding only after a thorough cleaning. Do not allow large, hard particles of abrasive to be near the mirror. They have the unpleasant ability to "spontaneously" seep into the grinding area and produce scratches. First use an abrasive with a particle size of 0.1-0.12 mm. The finer the abrasive, the smaller doses of it should be added. Depending on the type of abrasive, you need empirically select 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 catch (get stuck) on the grinder. It is convenient to keep the abrasive suspension in bottles with plastic tubes 2-3 mm in diameter inserted into the corks. This will make it easier to apply to the work surface and prevent large particles from clogging.

Check the grinding progress by looking through the mirror after rinsing with water. Large gouges left after clumsy grinding should completely disappear, the dullness should be completely uniform - only in this case, work with this abrasive can be considered complete. It is useful to work another extra 15-20 minutes, in order to grind with a guarantee not only unnoticed gouges, but also a layer of microcracks. After that, rinse the mirror, grinder, pallet, table, hands and proceed to sanding with another, smallest abrasive. Add the abrasive suspension evenly, in a few drops, shaking the bottle first. If you add too little abrasive suspension, or if there are huge deviations from the spherical surface, then the mirror can "grab". Therefore, put the mirror on the grinder and make the first movements very carefully, without much pressure. Particularly sensitive is the "gripping" of the mirror in the last stages of fine grinding. If such a threat has occurred, then in any case there is no need to rush. Work evenly (for 20 minutes) to warm up 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 knock a piece of wood on the edge of the mirror in the direction of its radius, observing all precautions. Do not forget that glass is a very fragile and low-thermal-conductivity material and with a very large temperature difference it cracks, as sometimes happens with a glass beaker if you pour boiling water into it. Quality control at the final stages of fine grinding should be carried out using a powerful magnifying glass or a microscope. In the final stages of fine sanding, the likelihood of scratches increases dramatically.

Therefore, we list the precautions against their appearance:
perform painstaking cleaning and washing of the mirror, pallet, hands;
do wet cleaning in the workroom after each approach;
try to remove the mirror from the grinder as little as possible. It is necessary to add the 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 on it, while large particles accidentally hitting the grinder will be crushed and will not scratch the plane of the glass disc in any way.
Individual 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 light rays incident at an angle of 15-20 °. After making sure that this is the case, sand it still without any pressure, quickly twirling to equalize the temperature from the warmth of your hands. If, on a thin layer of the finest abrasive, the mirror walks simply, with a slight whistle resembling a whistle through the teeth, this means that its surface is very close to spherical and differs from it only by hundredths of a micron. Our task in the subsequent polishing operation is not to spoil it in any way.

Mirror polishing

The difference between mirror polishing and fine grinding is that it is performed on soft material... High precision optical surfaces are polished with 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 polish, you first need to prepare a bitumen-rosin mixture in solvents. To do this, grind 20 g of grade IV petroleum bitumen and 30 g of rosin into small pieces, mix them and pour them into a bottle with a capacity of 100 cm3; then fill it with 30 ml of gasoline and 30 ml of acetone and close with a stopper. 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 sander 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. It is very important to distribute the drops evenly. Once the varnish has dried, the polishing pad is ready to use.

Then prepare a polishing suspension - a mixture of polishing powder and water in a ratio of 1: 3 or 1: 4. It is also convenient to store it in a corked bottle with a plastic tube. Now you have everything to polish your mirror. Moisten the mirror surface with water and put a few drops of polishing suspension on it. Then carefully place the mirror on the polishing pad and move. Polishing movements are the same as for fine sanding. 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 on to its cylindrical part with your fingers. The polishing will go on with almost no noise. If the room is quiet, you may hear a noise similar to 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 polishing pad "gets used" to this mode. The number of strokes is 80-100 per minute. Make the wrong movements from time to time. Check the condition of the polishing pad. Its drawing should be uniform. If necessary, dry it and drip the varnish in the right places, after shaking the bottle well with it. The polishing process should be monitored in light, using a strong magnifying glass or microscope with a magnification of 50-60 times.

The mirror surface should be polished evenly. It is very bad if the middle zone of the mirror or at the edges of the mirror is polished faster. This can happen if the surface of the pad is not spherical. This defect must be eliminated immediately by adding a bitumen-rosin varnish to the lowered places. The work usually comes to an end after 3-4 hours. If you look at 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 two to three times and making stops for 2-3 minutes every 5 minutes of work. This ensures that the temperature is equalized from the heat of friction and hands and the mirror acquires a more accurate shape of a spherical surface. So the mirror is ready. Now about design features and telescope details. The telescope views 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 prism of total internal reflection from large binoculars, a lens or a light filter from a camera, on the flat surfaces of which a reflective coating is applied. As an eyepiece of the telescope, 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 done very carefully.

The picture quality depends on their correct adjustment. The framed mirror should be secured with a slight gap. The mirror must not be allowed to be clamped radially or axially. 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 sub-mirror and then by adjusting the nuts of the primary mirror bezel. When the telescope is assembled, reflective coatings should be applied to the working surfaces of the mirrors and installed. The easiest way is to cover the mirror with silver. This coating reflects more than 90% of the light, but fades over time. Mastering the chemical deposition of silver and taking anti-tarnishing measures is the best solution for most amateur astronomers.

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. According to the ancient writers Plutarch and Polybius, the first person to practically use solar energy was Archimedes, who, with the help of some optical devices invented by him, managed to collect the sun's rays into a powerful beam and burn the Roman fleet.

In fact, 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 in 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 - solar concentrator - speaks for itself. This device receives the sun's rays and collects them into a single energy beam. The simplest hub is familiar to everyone from childhood. This is an ordinary biconvex lens, with which it was possible to burn out various figures, inscriptions, even whole pictures, when the sun's rays were collected by such a lens into a small point on a wooden board, a sheet of paper.

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

Refractory Solar Concentrator

A prismatic concentrator of solar radiation is devoid of this drawback. Moreover, such a device is also capable of concentrating part of the diffuse radiation, which significantly increases the power of the light beam. The triangular 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 rear face reflects, and radiation is already coming out of 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 refractory, reflex concentrators work on the principle of collecting reflected sunlight into an energy beam. By their design, they are divided into flat, parabolic and parabolic cylindrical concentrators. If we talk about the effectiveness of each of these types, then 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 (reflex) solar concentrators

Practical application of solar concentrators

Actually, the main task of any solar concentrator is to collect the sun's radiation into a single energy beam. And you can use this energy in different 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 cooking oven.

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 the order of 300 ° C - 400 ° C. If the focus of such a comparatively small mirror place, for example, a stand for a kettle, frying pans, then you get a solar oven, on which you can very quickly cook food, boil water. A focused heater with a coolant will allow you to quickly heat up even running water, which can then be used for household purposes, for example, for a shower, washing dishes.

The simplest schemes for heating water with a solar concentrator

If a Stirling engine of a suitable power is placed in the focus of a parabolic mirror, then a small thermal power plant can be obtained. For example, Qnergy has developed and commercialized 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 with a capacity of 3500 watts. The output of the inverter is a standard voltage of 220 volts 50 hertz. This is quite enough to provide a house for a family of 4 people, a summer cottage with electricity.

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. In industrial helium plants, special tracking systems are used 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 will hardly be advisable to use such tracking devices, since their cost can significantly exceed the cost of a simple reflector on an ordinary 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 concentrator will be used, and then, based on this, choose an 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 plate.

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 the concentrator is supposed to be used as a solar oven, it is recommended to cut a hole with a diameter of about 5 - 7 centimeters in the center of the plate. A bracket with a cookware support (burner) will be passed through this hole. This will keep the food container immobile when the reflector is turned in the sun.

If the plate is small in diameter, it is also recommended to cut the strips into pieces about 10 cm long. Glue each piece separately, carefully adjusting the joints. When the reflector is ready, it should be mounted on a support. After that, it will be necessary to determine the focal point, since the optical focal 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 board and thick gloves. Then you need to direct the mirror directly to the sun, catch a sunbeam on the board and, bringing the board closer or away relative to the mirror, find the point where this bunny will have its minimum size - a small point. Gloves are needed in order to protect your hands from burns if they accidentally fall into the range of the beam. Well, when the focal point is found, it only remains to fix it and mount the necessary equipment.

Options self-made solar concentrator there are many. In the same way, you can make a Stirling engine from the materials at hand. And this engine can be used for a variety of purposes. How long will there be enough imagination, desire and patience.