DIY mini spyglass. How to make a reliable and powerful telescope yourself at home

So, you have decided to make a telescope and are getting down to business. First of all, you will learn that the simplest Spyglass consists of two biconvex lenses - the objective and the eyepiece, and that the magnification of the telescope is obtained by the formula K = F / f (the ratio of the focal lengths of the objective (F) and the eyepiece (f)).

Armed with this knowledge, you go digging through boxes of different junk, in the attic, in the garage, in the shed, etc. with a clearly defined goal - to find more different lenses. These could be glasses from glasses (preferably round ones), watch magnifiers, lenses from old cameras, etc. Having collected a supply of lenses, start measuring. You need to choose a lens with a larger focal length F and an eyepiece with a smaller focal length f.

Measuring focal length is very simple. The lens is directed at some light source (a light bulb in the room, a lantern on the street, the sun in the sky or just a lit window), a white screen is placed behind the lens (a sheet of paper is possible, but cardboard is better) and moves relative to the lens until It will not produce a sharp image of the observed light source (inverted and reduced). After this, all that remains is to measure the distance from the lens to the screen with a ruler. This is the focal length. You are unlikely to cope with the described measurement procedure alone - you will need a third hand. You'll have to call an assistant for help.

The resulting image will be enlarged, but still upside down. What you are now holding in your hands, trying to maintain the achieved relative position of the lenses, is the desired optical system. All that remains is to fix this system, for example, by placing it inside a pipe. This will be the spyglass.

You can obtain a wraparound system with one coaxial additional lens by placing it at a distance of approximately 2f from the eyepiece (the distance is determined by selection).

It is interesting to note that with this version of the reversing system, it is possible to obtain greater magnification by smoothly moving the additional lens away from the eyepiece. However, strong magnification You won’t be able to get it if you don’t have a very high-quality lens (for example, glass from glasses). The larger the lens diameter, the greater the magnification obtained.

This problem is solved in “purchased” optics by composing a lens from several lenses with different refractive indices. But you don’t care about these details: your task is to understand the circuit diagram of the device and build the simplest working model according to this scheme (without spending a penny).

The process of making, assembling and customizing is very exciting.

Below is my telescope with 80x magnification - almost like a telescope.

It's safe to say that everyone has dreamed of taking a closer look at the stars. You can use binoculars or a spotting scope to admire the bright night sky, but you are unlikely to be able to see anything in detail through these devices. Here you will need more serious equipment - a telescope. To have such a miracle of optical technology at home, you need to lay out 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 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 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 thing at all. In order to figure out what’s what, it’s 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 will also be able to figure out whether this activity is interesting to you. If you are passionate 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 make out its four main satellites. The rings of Saturn, familiar to us from the pages of textbooks, can also be seen using 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 part, the light emitted by celestial bodies is collected. How distant bodies can be seen, as well as the magnification of the device, depends on the diameter of the lens. The second member of the tandem, the eyepiece, is designed to enlarge the resulting image so that our eye can admire the beauty of the stars. Now about the two most common types 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 found quite easily in specialized stores. Buying a mirror for a reflector will not be cheap, but self-production will be impossible for many.

Therefore, as has already become clear, we will be assembling a refractor, and not a reflecting telescope. Let's finish 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 didn’t always radiate joy and self-confidence. But first things first... How to make a telescope? Selecting 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 generally have a concave-convex shape and are poorly suited for a telescope, although if you have them on hand, you can use them. It is recommended to use long-focal lenses with a biconvex shape. As an eyepiece, you can take a regular magnifying glass with a thirty-millimeter diameter. If it is possible to get an eyepiece from the microscope, then it is certainly worth taking advantage of. It is also perfect for a telescope. What should we make the housing for our future optical assistant from? Two pipes of different diameters made of cardboard or thick paper are perfect. One (the shorter one) 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 the eyepiece unit, and it is recommended to make the main one a meter long. If you don’t have the necessary blanks at hand, it doesn’t matter, the body can be made from an unnecessary roll of wallpaper. To do this, the wallpaper is wound in several layers to create the required thickness and rigidity and glued. How to make the diameter of the inner tube depends on what kind of lens we use. Telescope stand Very important point in creating your own 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 camera tripod, which is equipped with a moving head, as well as fasteners that allow you to fix various provisions housings. Assembling the telescope The lens for the objective is fixed in a small tube with the convex outward. It is recommended to fasten it using 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 these are lenses from K8. Because condensers (and these are undoubtedly condenser lenses) often have a pair of lenses, one of which is made of crown, the other of which is made of flint. A flint lens is absolutely unsuitable as a blank for the main mirror for a number of reasons (one of which is great sensitivity to temperature). A flint lens is perfect as a base for a polishing pad, but it won’t work for grinding, since the flint lens has much greater hardness and grindability than the crown. In this case, use a plastic sander.

Secondly, I strongly advise you to carefully read not only Sikoruk’s book, but also “The Telescope of an Amateur Astronomer” by M.S. Navashina. And with regard to testing and measuring the mirror, you should focus specifically on Navashin, who describes this aspect in great detail. Naturally, it is not worth making a shadow device exactly “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 quality of measurements on an uncoated mirror, and will also allow bring the “star” close to the knife; it is advisable to use a rail from an optical bench, etc. as a base). You need to approach the manufacture of a shadow device with great care, since the quality of your mirror will be determined by how well you make it.

In addition to the above-mentioned rail from the optical bench, a useful “swag” for its manufacture is a support from a lathe, which will be a wonderful device for smoothly moving a 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 attach a webcam to the 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 the shadow patterns 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 strong, and movement must be without backlash. Organize a pipe or tunnel along the entire path of the rays - this will reduce the impact of convection currents, and in addition, will allow you to work in the light. In general, convection currents are the bane of any mirror testing method. Fight them with all possible means.

Invest in good abrasives and resin. Cooking resin and sanding abrasives is, firstly, an unproductive expenditure of effort, 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 impeccable rigidity of the structure. Here is an absolutely ideal wooden barrel, covered with rubble, around which Chikin, Maksutov and other “founding fathers” once walked. 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. It is better to equip a barrel for roughing and rough grinding outdoors, but fine grinding and polishing is a matter for indoors. constant temperature and without drafts. An alternative to the barrel, especially at the stage of fine grinding and polishing, is the floor. It is, of course, less convenient to work on your knees, but the rigidity of such a “machine” is ideal.

Need to Special attention pay attention to securing the workpiece. A good option unloading the lens is gluing it to a “patch” of minimal size in the center and three stops near the edges, which should only touch, but not put pressure on the workpiece. The patch needs to be sanded flat and brought to No. 120.

To prevent scratches and chips, it is necessary to chamfer the edge of the workpiece before roughing and bring it to a fine grind. The width of the chamfer should be calculated so that it is preserved until the end of work with the mirror. If the chamfer “ends” during the process, it must be resumed. The chamfer must be uniform, otherwise it will be a source of astigmatism.

The most rational way to grind is with a ring or a reduced grinding blade in the “mirror below” position, but given the small size of the mirror, you can also do it according to Navashin - mirror on top, grinding blade normal size. Silicon carbide or boron carbide is used as an abrasive. When stripping, you need to be careful not to refine the astigmatism and “go” into the hyperboloid shape, which such a system has a clear tendency to do. The latter can be avoided by alternating a normal stroke with a shortened one, especially towards the end of the stripping. If during grinding the surface initially obtained is as close as possible to a sphere, this will dramatically speed up all further grinding work.

Abrasives for grinding - starting from number 120 and finer, it is better to use electrocorundum, and for larger ones, carborundum. The main characteristic of abrasives that one should strive for is the narrowness of the particle distribution spectrum. If the particles in a given specific 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 “stairs” should be much flatter, and we will arrive at polishing with “waves” on the surface, which will then take a long time to get rid of.

The shaman's trick against this with not the best abrasives is to polish the mirror with an even finer abrasive before changing the number to a finer 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 quite short. Why this works - I don't know. With a good abrasive, you can grind after number 220 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 the 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 grinding stage (even not fine) is to polish the surface by rubbing suede with polish until it shines, after which you can easily determine the focal point 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 avoid a “broken” surface.

The process of polishing and figuration is probably described so well and in detail that it would be wiser not to go into it but to send 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 slower than polyrite, and less risk"skip" the required form.

Directly behind the lens, further along the pipe, it is necessary to equip a diaphragm in the form of a disk with a thirty-millimeter hole exactly in the middle. The purpose of the aperture is to eliminate image distortion caused by the use of a single lens. Also, installing it will affect the reduction of light that the lens receives. The telescope lens itself is mounted near the main tube. Naturally, the eyepiece assembly cannot do without the eyepiece itself. First you need to prepare fastenings for it. They are made in the form of a cardboard cylinder and are similar in diameter to an eyepiece. The fastening is installed inside the pipe using two disks. They are the same diameter as the cylinder and have holes in the middle. Setting up the device at home You need to focus the image using the distance from the lens to the eyepiece. To do this, the eyepiece assembly moves in the main tube.

Since the pipes must be well pressed together, the required position will be securely fixed. It is convenient to perform the tuning process on large bright bodies, for example, the Moon; a neighboring house will also work. When assembling, it is very important to ensure that the lens and 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 size of the aperture. By varying its diameter, you can achieve the optimal picture. Using optical lenses of 0.6 diopters, which have a focal length of approximately two meters, you can increase the aperture and make the zoom much closer on our telescope, but you should understand that the body will also increase.

Watch out - 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 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, you need to remember very important rule: you cannot look at the Sun through zooming devices, especially a home telescope, without special means protection.

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

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

For the body, 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 unit) is inserted into a long one (about 1 m, main). The inner diameter of the main pipe 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). A disk is installed immediately behind the lens - 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 resulting from 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 have to make an eyepiece mount from cardboard. It will consist of a cylinder equal in diameter to the eyepiece. This cylinder will be attached to inside pipes with two disks with a diameter equal to the inner diameter of the eyepiece 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 unit in the main tube, and fixation will occur due to friction. It is better to focus 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 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 astronomy enthusiast to make a Newtonian system reflector.

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

The concave spherical surface of a polished mirror reflects only about 5% of the light incident on it. Therefore, it must be coated with a reflective layer of aluminum or silver. Aluminize the mirror in home environment impossible, but silvering is quite possible.

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

Set of eyepieces: 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, and 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 towards the North Star.

Such means are considered to be light filters and a method of projecting an image onto a screen. What if you couldn’t assemble a telescope with your own hands, but you really want to look at the stars? If for some reason it is impossible to assemble a homemade telescope, then do not despair. You can find a telescope in a store for a reasonable price. The question immediately arises: “Where are they sold?” Such equipment can be found in specialized astro-device stores. If there is nothing like this in your city, then you should visit a photographic equipment store or find another store that sells telescopes. If you are lucky, there is a special shop, and even with professional consultants, then you are definitely in the right place. Before going, it is recommended to look at an overview of telescopes. First, you will understand the characteristics of optical devices. Secondly, it will be more difficult to deceive you and slip you a low-quality product.

Then you will definitely not be disappointed in your 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’s very convenient: you look for the device you need, and then order it. However, you may come across the following nuisance: after a long selection, it may turn out that the product is no longer in stock. A much more unpleasant problem is the delivery of goods. It is no secret that a telescope is a very fragile thing, so only fragments can be delivered to you. It is possible to purchase a telescope by hand.

This option will allow you to save a lot of money, but you should be well prepared so as not to buy a broken item. A good place to find a potential seller is astronomer forums. Price per telescope Let's consider some price categories: About five thousand rubles. Such a device will correspond to the characteristics of a telescope made with your own hands 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 meager, 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.

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

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

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

A diagonal mirror is made in small sizes, 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 - the telescope requires an optically more accurate surface. Therefore, as a diagonal mirror, you can use a flat surface of a plane-concave or plane-convex 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 the cone of rays that are reflected by the main mirror. With a rectangular or elliptical mirror shape, the sides or axes have a ratio of 1:1.4 to each other.

The lens and eyepiece of a homemade reflecting telescope are mounted mutually perpendicular to 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 board 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 to this board with 4 pieces of thick-walled rubber tube, mounted on screws. For better fixation, you can place plastic washers under the heads of the screws (they cannot clamp the mirror itself).

The tube 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 carpenter or casein glue, then insert the cardboard tube into the metal stiffening rings. Metal is also used to make a bowl for the frame of the main mirror of a homemade telescope and a pipe cover.

The length of the pipe (tube) of a homemade reflecting telescope should be equal to the focal length of the main mirror, and the internal diameter of the pipe should be 1.25 times the diameter of the main mirror. The inside of the tube of a homemade reflecting telescope should be “blackened”, i.e. cover it with matte black paper or paint it with matte black paint.

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

Homemade reflecting telescope Before use, it must be installed on a special stand - a mount. You can purchase either 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 following materials.

Surely a beginner will have no need for a mirror camera with an astronomical cost. This is simply, as they say, a waste of money. Conclusion As a result, we got acquainted with important information about how to make a simple telescope with your own hands, and some of the nuances of buying a new device for observing the stars. In addition to the method that we have considered, there are others, but this is a topic for another article. Whether you've built a telescope at home or purchased a new one, astronomy will take you into the unknown and provide experiences you've never experienced before.

Pipe from spectacle glasses- This is essentially the simplest refractor with a single lens instead of an objective. Rays of light coming from the observed object are collected in a tube by a lens lens. To eliminate the rainbow coloring of the image and chromatic aberration, two lenses made of different types of glass are used. 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 under amateur conditions. It is difficult to get a good, even small, lens lens for a telescope.

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

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 main optical axis. 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 was cut for the exit of the cone of rays and the eyepiece tube 5 was strengthened. Despite this. that the reflective surface is processed with very high precision - the deviation from the given size should not exceed 0.07 microns (seven hundred thousandths of a millimeter) - the manufacture of such a mirror is quite accessible to a schoolchild.

First cut out the main mirror.

The main concave mirror can be made from ordinary mirror, table or display glass. It must have sufficient thickness and be well annealed. Poorly annealed glass warps greatly when the temperature changes, and this distorts the shape of the mirror surface. Plexiglass, plexiglass and other plastics are not suitable at all. The thickness of the mirror should be slightly more than 8 mm, the diameter no more than 100 mm. A slurry of emery powder or carborundum with water is applied under a piece of metal pipe of suitable diameter with a wall thickness of 02-2 mm. Two disks are cut from mirror glass. You can manually cut a disk with a diameter of 100 mm from glass 8 - 10 mm thick in about an hour to make the work easier, you can use a machine (Fig. 2).

The frame is strengthened on the base 1

3. An axis 4, equipped with a handle 5, passes through the middle of its upper crossbar. A tubular drill 2 is attached to the lower end of the axis, and a weight b is attached to the upper end. The drill axis can be equipped 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 - sanding

If you place one glass disk on top of another and, having smeared the contacting surfaces with a mixture of abrasive powder and water, move the upper disk towards and away from you, at the same time evenly rotating both disks in opposite directions, then they will be ground to one another. The lower disk gradually becomes more convex, and the upper one 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 main mirror; . P 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 stage is polishing.

The instrument is the same second glass Disc. It needs to be turned into a polishing pad, and to do this, apply a layer of resin mixed with rosin to the surface (the mixture gives the polishing layer greater hardness).

The resin for polishing pad is prepared like this. Melt the rosin 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 in advance the ratio of rosin and resin. After cooling 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. You cannot bring the resin to a boil and form bubbles; it will be unsuitable for work. A network of longitudinal and transverse grooves is cut on the layer of polishing mixture so that the polishing substance and air circulate freely during operation and the resin areas provide good contact with the Mirror. Polishing is done in the same way as sanding: the mirror moves back and forth; In addition, both the polishing pad and the mirror are turned little by little in opposite directions. To obtain the most accurate sphere possible, during grinding and polishing it is very important to maintain a certain rhythm of movements, uniformity in the length of the “stroke” and the rotations of both glasses.

All this work is done on a simple homemade machine (Fig. 3), similar in design to a pottery machine. A rotating wooden table with an axis passing through the base is placed on a thick board base. The grinder or polishing pad is mounted on this table. To prevent the wood from warping, it is impregnated with oil, paraffin or waterproof paint.

The Fouquet device comes to the rescue

Is it possible, without going to a special optical laboratory, to check how accurate the surface of the mirror is? It is possible 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 micron. The famous Soviet optics scientist 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 very device, assembled from a kerosene lamp, a piece of blade from a hacksaw and wooden blocks to test it. . Here's how it works (Figure 4)

A point source of light I, for example, a puncture in the 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 - a “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. But a spherical surface (not a sphere) cannot 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 picture” (Fig. 5), from which we can find out what deviations from the sphere there 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 place your finger on the surface of the mirror for a few seconds and then look using a shadow device; then in the place where the finger was applied, a mound with quite

a noticeable shadow gradually disappearing. The shadow device clearly showed an insignificant elevation formed from the heating of a section of the mirror upon contact with a finger. If “Foucault’s knife extinguishes the entire mirror at the same time, then its surface is truly an exact sphere.

Several Yet important advice

Once the mirror has been polished and its surface precisely shaped, the reflective concave surface must be aluminized or silver plated. The reflective layer of aluminum is very durable, but it is possible to cover a mirror with it only in a special installation under vacuum. Alas, fans do not have such settings. But you can silver plate a mirror at home. The only pity is that silver fades quite quickly and the reflective layer has to be renewed.

A good primary 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 geodetic instruments. In extreme cases, a single biconvex or plano-convex lens can serve as an eyepiece.

The tube (tube) and the entire installation of the telescope can be made in a wide variety of options - from the simplest, where the material is cardboard, planks and wooden blocks (Fig. 6), to very advanced ones. with Parts and specially cast parts 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 main thing is patience

A 7th-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 should one feel who gets acquainted with space with the help of the most precise optical instrument - a telescope, made with his own hands!

The hardest part to produce yourself is the main mirror. We recommend you a new, fairly 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 for fine grinding and especially for polishing a mirror. Only when given condition you can build a telescope that is no 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 15-20mm thick.

You can use a lens from a photo enlarger condenser, which are often sold in shopping centers photo products. Or glue thin glass disks with epoxy glue, which can be easily cut with a diamond or roller glass cutter. Make sure that the adhesive joint is as thin as possible. A “layered” mirror has some advantages over a solid one - it is not as susceptible to warping when temperature changes environment, and therefore gives an image of better quality.

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

Abrasive powders for grinding can be made from carborundum, corundum, emery or quartz sand. The latter polishes slowly, but despite all the above, the quality of the finish is noticeably higher. The 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. Apart from this, smaller powders with grain sizes will be required.

If the powders are in finished form It is not possible to purchase, but it is quite possible to prepare them yourself by crushing small pieces of an abrasive grinding wheel in a mortar.

Rough grinding of the mirror.

Secure the sanding pad to a stable stand or table with the working side facing up. You should take care of the painstaking cleaning of your home grinding “machine” after replacing abrasives. Why should a layer of linoleum or rubber be laid on its surface? A special tray is very convenient, which, together with the mirror, can then be removed from the table after work. Rough grinding is done using a reliable “old-fashioned” method. Mix abrasive with water in a ratio of 1:2. Spread about 0.5 cm3 over the surface of the sanding pad. the resulting slurry, place the mirror blank with the outer side down and begin grinding. Hold the mirror with two hands, this will protect it from falling, and the correct position of the hands will quickly and accurately obtain the desired radius of curvature. When grinding, make movements (strokes) in the direction of the diameter, evenly rotating the mirror and grinder.

Try from the very beginning to accustom yourself to the subsequent rhythm of work: for every 5 strokes, turn the mirror 60° in your hands. Work rate: approximately 100 strokes per minute. As you move the mirror back and forth across the surface of the sanding pad, try to keep it in a state of stable equilibrium on the circumference of the sanding pad. As grinding progresses, the crunch of the abrasive and the intensity of grinding decreases, the plane of the mirror and the grinding pad becomes contaminated with spent abrasive and particles of glass with water - sludge. It must be washed off from time to time or wiped with a damp sponge. After sanding for 30 minutes, check the size of the indentation using a metal ruler and safety razor blades. Knowing the thickness and number of blades that fit into the gap 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 required value (in our case - 0.9mm). If the grinding powder good quality, then rough grinding can be completed in 1-2 hours.

Fine grinding.

For fine finishing, the surfaces of the mirror and the grinding wheel are ground against each other on a spherical surface with the highest precision. Grinding is done in several passes using increasingly fine abrasives. If during coarse grinding the center of pressure was located near the edges of the grinder, then during fine grinding it should be no more than 1/6 of the workpiece diameter from its center. At times it is necessary to make, as it were, erroneous movements of the mirror along the surface of the grinding pad, now to the left, now to the right. Start fine sanding only after thorough cleaning. Large, hard particles of abrasive should not be allowed near the mirror. They have the 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, you need to experimentally select its concentration with water in suspension and the portion value. The time of its production (suspension), as well as the frequency of sludge removal. 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 with a diameter of 2-3 mm inserted into the stoppers. This will make it easier to apply it to the work surface and protect it from clogging with large particles.

Check the grinding progress by viewing the mirror against the light after rinsing with water. Large chips left after clumsy grinding should completely disappear, the dullness should be completely uniform - only in this case can the work with this abrasive be considered complete. It is useful to work an extra 15-20 minutes in order to ensure that you polish not only unnoticed gouges, but also the layer of microcracks. After this, rinse the mirror, sanding pad, tray, table, hands and proceed to sanding with another, smallest abrasive. Add the abrasive suspension evenly, a few drops at a time, shaking the bottle beforehand. If you add too little abrasive suspension or if there are huge deviations from the spherical surface, then the mirror can “stick”. Therefore, you need to place the mirror on the grinding pad and make the first movements very carefully, without much pressure. Particularly ticklish is the “grabbing” of the mirror on late stages fine grinding. If such a threat has occurred, then under no circumstances should you rush. Take the trouble to evenly (over 20 minutes) heat the mirror with the grinding pad under the jet warm water to a temperature of 50-60°, and then cool them. Then the mirror and the grinding pad will move apart. You can tap 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 material and has low thermal conductivity, 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. At the final stages of fine grinding, the likelihood of scratches increases dramatically.

Therefore, we list the precautions against their occurrence:
perform thorough cleaning and washing of the mirror, tray, hands;
do wet cleaning in the workroom after each approach;
try to remove the mirror from the grinding pad as little as possible. It is necessary to add abrasive by moving the mirror to the side by half its diameter, evenly distributing it according to the surface of the grinding pad;
Having placed the mirror on the grinding pad, press it, and large particles that accidentally fall on the grinding pad will be crushed and will not scratch the plane of the glass blank.
Individual scratches or pits will not spoil the image quality. However, if there are a lot of them, they will reduce the contrast. After fine grinding, the mirror becomes translucent and perfectly reflects light rays falling at an angle of 15-20°. Once you are sure that this is the case, grind it without any pressure, quickly turning it to equalize the temperature from the warmth of your hands. If on a thin layer of the finest abrasive the mirror moves simply, with a slight whistle, reminiscent of whistling through teeth, then this means that its surface is very close to spherical and differs from it only by hundredths of a micron. Our task during 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 a 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 the hard grinding pad (it is used as the basis 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 20 g of grade IV petroleum bitumen and 30 g of rosin into small pieces, mix them and pour them into a 100 cm3 bottle; then pour 30 ml of gasoline and 30 ml of acetone into it and close with a stopper. To speed up the dissolution of rosin and bitumen, shake the mixture periodically, and after a few hours the varnish will be ready. Apply a layer of varnish to the surface of the sanding pad and let it dry. The thickness of this layer after drying should be 0.2-0.3 mm. After this, pick up the varnish with a pipette and drop one drop at a time onto the dried layer, preventing the drops from merging. What is very important is to distribute the drops evenly. After the varnish has dried, the polishing pad is ready for 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 bottle with a stopper, equipped with a plastic tube. Now you have everything you need to polish the mirror. Wet the surface of the mirror with water and drop a few drops of polishing suspension onto it. Then carefully place the mirror on the polishing pad and move it around. The movements during 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 proceed almost silently. If the room is quiet, you may hear a noise that sounds like breathing. Polish slowly, without pressing too hard on the mirror. It is important to set a mode in which the mirror moves forward quite tightly under load (3-4 kg), but goes back easily. The polishing pad seems to “get used” to this regime. The number of strokes is 80-100 per minute. Make incorrect movements from time to time. Check the condition of the polishing pad. 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 through light, using a strong magnifying glass or 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 at the edges is polished faster. This can happen if the surface of the polishing pad is not spherical. This defect must be eliminated immediately by adding bitumen-rosin varnish to low areas. 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, 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 stopping for 2-3 minutes every 5 minutes of work. This ensures temperature equalization from the heat of friction and hands and the mirror acquires a more accurate spherical surface shape. So, the mirror is ready. Now about the design features and details of the telescope. Types of the telescope are shown in the sketches. You will need few materials, and they are all available and relatively cheap. A full prism can be used as a secondary mirror. internal reflection from large binoculars, a lens or filter from a camera, the flat surfaces of which have a reflective coating 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 should not be allowed to be jammed in the radial or axial direction. In order for a telescope to provide an image High Quality, it is necessary that its optical axis coincides with the direction towards the object of observation. This adjustment is made by changing the position of the secondary auxiliary mirror, and then by adjusting the adjustment nuts of the primary 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 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.

Let's find out the focal length we need. To do this, let's shine light on the lens by placing a piece of paper behind it. Now slowly move the sheet away until the light source is displayed on it. We measure the distance between the leaf and the lens. In this way, from all the lenses found in the house, you must choose the one with the largest distance and the one with the smallest. The first will be the lens, and the last will be the eyepiece.

Step 2

We take the eyepiece with our right hand, our lens with our left hand and carefully examine some object through them, bringing them closer and apart until the object becomes clear. We measure the resulting length.

Step 3

Step 4

Now let's assemble these lenses into a telescope. Take two sheets of thicker paper and paint one side black. Fold it so that the black one is on the inside. We insert the lens into the first tube, and our eyepiece and wrapping lens into the other. We attach them to the paper with plasticine or superglue. We push the pipes into one another so that they fit quite firmly. If necessary, you can secure it with tape.

Now I propose to familiarize yourself with how to make a simple telescope from available materials.

To make it you will need at least two lenses (lens and eyepiece).
Any long-focus lens from a photo or movie camera, a theodolite lens, a level lens, or any other optical device will be suitable as a lens.
We will begin making the tube by determining the focal lengths of the lenses at our disposal and calculating the magnification of the future device.
The method for determining the focal length of a converging lens is quite simple: we take the lens in our hand and, placing its surface towards the sun or lighting device, we move it up and down until the light passing through the lens gathers into a small point on the screen (sheet of paper ). Let us achieve a position in which further vertical movements lead to an increase in the spot of light on the screen. By measuring the distance between the screen and the lens using a ruler, we obtain the focal length of this lens. On photo and movie camera lenses, the focal lengths are indicated on the body, but if you can’t find a ready-made lens, it doesn’t matter, it can be made from any other lens with a focal length not exceeding 1 m (otherwise the telescope will turn out to be long and will lose its compactness - after all, the length of the tube depends on the focal length of the lens), but a lens that is too short-focus is not suitable for this purpose - a short focal length will affect the magnification of our telescope. As a last resort, the lens can be made from spectacle glasses, which are sold in any optician.
The focal length of one such lens is determined by the formula:
F = 1/Ф = 1 m,
Where F – focal length, m; F – optical power, dioptre. The focal length of our lens, consisting of two such lenses, is determined by the formula:
Fo = F1F2/F1 + F2 – d,
Where F1 and F2 are the focal lengths of the first and second lenses, respectively; (in our case F1 = F2); d is the distance between the lenses, which can be neglected.
Thus Fo = 500 mm. Under no circumstances should lenses be placed with concavities (menisci) facing each other - this will increase spherical aberration. The distance between lenses should not exceed their diameter. The diaphragm is made of cardboard, and the diameter of the diaphragm hole is slightly smaller than the diameter of the lenses.
Now let's talk about the eyepiece. It is best to use a ready-made eyepiece from a binocular, microscope or other optical device, but you can get by with a magnifying glass of suitable size and focal length. The focal length of the latter should be in the range of 10 – 50 mm.
Suppose that we managed to find a magnifying glass with a focal length of 10 mm, all that remains is to calculate the magnification of the device G, which we obtain by collecting optical system from this eyepiece and lens from spectacle glasses:
G = F/f = 500 mm/10 mm = 50,
Where F is the focal length of the lens; f – focal length of the eyepiece.
It is not necessary to look for an eyepiece with the same focal length as in the example given; any other lens with a short focal length will do, but the magnification will correspondingly decrease if f increases, and vice versa.
Now, having selected the optical parts, we will begin to manufacture the bodies of the telescope and eyepiece. They can be made from suitable-sized scraps of aluminum or plastic pipe, or they can be glued together from paper on special wooden blanks using epoxy glue.
The lens tube is made 10 cm shorter than the focal length of the lens, the eyepiece tube usually has a length of 250 - 300 mm. Internal surfaces pipes are coated with matte black paint to reduce scattered light.
Such a pipe is easy to manufacture, but has one significant drawback: the image of objects in it will be “upside down”. If for astronomical observations This drawback does not matter, but in other cases it causes some inconvenience. The disadvantage can be easily eliminated by introducing a diverging lens into the design, but this will negatively affect image quality and the ability to magnify, and choosing a suitable lens is quite difficult.

With the help of a homemade telescope, you can view the surface of the Moon and even some planets, so it will serve well for those who are interested in astronomy. First you need to make a lens. You need to take a biconvex (round) lens for glasses from +1 diopter (focal length 100 centimeters) to +2 diopters (focal length 50 centimeters). (How to determine the focal length by diopters and vice versa, see the article). For the eyepiece, we will select another spectacle glass or a small magnifying glass with a focal length of 2-4 centimeters (from +50 to +25 diopters).

Magnifying glasses are usually sold in plastic cases that indicate the magnification level. For example, the number 2.5 means that the magnifying glass magnifies 2.5 times. To find out the number of diopters, this number must be multiplied by 4. A magnifying glass that magnifies 2.5 times has +10 diopters (2.5x4=10). For this purpose, it is advisable to choose a magnifying glass with a magnification of 6 to 12.5 times.

Both lenses are mounted in tubes glued together from paper and blackened on the inside. The magnifying glass can be glued into the eyepiece tube along with a plastic rim; on it you just need to cut off the protrusion that fastens the rim to the case. The total length on both tubes should be 5-10 centimeters greater than the focal lengths of both lenses. For example, if you took glass with a focal length of 50 centimeters for the lens, and 2 centimeters for the eyepiece, then the total length of the two tubes should be 57-62 centimeters.

First, we glue a tube 15-20 centimeters long along the diameter of the eyepiece lens, then along the diameter of the lens. The first tube should fit into the second with slight friction. If the difference in lens diameters is too great, then the eyepiece tube must be made thicker.

We will attach the lenses to the ends of the tubes as described in the article: . To protect the glass from dust and scratches, it is advisable to make cardboard covers for the tubes.

How to use a homemade telescope

We will move the eyepiece tube in the larger tube until we find a position at which the observed body becomes clearly visible. You can calculate in advance what magnification the telescope gives (or rather, the degree of approach of the observed object to the eye): the focal length of the lens must be divided by the focal length of the eyepiece. In the above example (with a lens with a focal length of 50 centimeters and an eyepiece with a focal length of 2 centimeters), the magnification will be 25 times (50:2 = 25).

For long periods, it is advisable to install it on a tripod so that the tube can be rotated to the sides, raised and lowered. To do this, we will attach a tube bent from thick tin or cut from some long pipe onto the round rod of the tripod. We will insert the head of the tripod into the tube from above, to which we will attach a clamp bent from tin with screws. The lens tube is secured in the clamp. By tilting and lifting the clamp, you can change the position of the telescope vertically, and by turning the tripod head in the tube - horizontally.

How to make a spyglass

A telescope is made exactly like a telescope. Only it needs different lenses. For the eyepiece they take a lens from -16 to -20 diopters, and for a lens - from +4 to +6 diopters. Thus, in a telescope, like in binoculars, one is concave and the other is concave. As a result, the magnification level decreases, but the sharpness increases. A tripod for the telescope is not needed; it is held in your hands, so you can take it on hikes.

When observing through a telescope or spotting scope, the edges of the visible image may be unclear or blurry. To enhance clarity, you need to apply an aperture to the lens - a ring of black paper with a very narrow rim. You should not reduce the aperture opening too much (increase the rim of the ring), as the aperture will reduce the amount of light entering the lens and the image will darken.