What to make a parabolic base from.

home The starry sky has always attracted researchers; probably everyone at least once in their life dreamed of discovering some star or constellation and naming it in honor of a person close to them. I present to your attention a small guide, which consists of two parts which provide detailed description , How do from scratch their hands wooden telescope. This part will show you how you can make key element telescope: primary.

mirror A good mirror will help you see various details of the Moon and planets solar system and other objects deep space

while a poor quality mirror will give you only blurry outlines of objects. Telescope mirrors require an extremely precise surface. In most cases, excellent quality mirrors are achieved by hand polishing rather than machine polishing. This is one of the reasons why some people prefer to make their own mirrors rather than buy cheap industrial designs. The second reason is that you will buy necessary knowledge for the production of high quality optical instruments

, and as you know, you can’t carry knowledge behind your shoulders.

• Step 1: Materials
• The blank glass is made of a material with a low coefficient of expansion (Pyrex, borosilicate glass, Duran 50, Cerodur, etc.);
• Silicon carbide of various grain sizes (60, 80, 120, 220, 320 units);
• Aluminum oxide (25, 15, 9 and 5 microns);
• Cerium oxide;
• Resin;
• Grindstone;
• Waterproof plaster (dental plaster);
• Ceramic tile;

Epoxy adhesive.

Step 2: Preparing the workpiece

Glass blanks often come with marks on the surface. The “round mark” in the lower part was left by the stove, and the upper marks appeared as a result of the temperature difference when the glass cooled. Let's start by treating the edges of the glass to limit the risk of chipping. A whetstone is an excellent tool for this operation. Don't forget about the funds personal protection

The bottom of the mirror should be as flat as possible (before you start working on it). To level the surface we will use coarse carborundum (silicon carbide #60). Spread the powder and water on a flat surface and rub the glass over it. After a few seconds, you will see a gray paste. Rinse it off and add wet sand. Continue until the surface is clear of holes and potholes.

Step 3:

This jig will be used to create a concave surface on a glass piece.

Let's cover the glass plastic film. Let's make a cardboard cylinder around the workpiece and pour plaster inside. Let it dry, then remove the cardboard. Carefully separate the glass and remove burrs from the edges.

Step 4: Ceramic Tile Covering

We need a hard surface to polish the glass. That is why the convex part of the workpiece must be covered with ceramic tiles.

Glue the tiles onto gypsum base epoxy resin.

Please note that placing tiles or holes in the center should be avoided. Instead, offset the tile slightly to avoid any central imperfection on the mirror surface.

Step 5: Start Sanding

Let's put some wet sand on the surface of the tile and start rubbing the glass on it.

After several passes, turn the mirror and continue sanding in the other direction. This provides good processing, from all angles and will prevent mistakes.

Step 6:

Continue sanding until we get the desired bend. To estimate curvature, you must use the calculator from the Sagitta measurement set.

If you want to build a telescope for observing planets, you will need a larger focal ratio (F/8 or higher).

On the other hand, if you want to contemplate the expanse of the galaxy and stellar nebulae, you will need a small focal ratio (F/4, for example).

Focal ratio F/4.75. The sagitta of my 20 cm mirror is 0.254 cm.

Step 7: Smooth the Surface

Once the required curvature is achieved, you need to smooth the surface while maintaining the same curvature.

Mark large flaws with a marker and continue sanding until they are completely removed. This will provide visual confirmation that you can switch to a finer abrasive.

Let's move on to #320 silicon carbide. Once you have reached this step, you should start to see some reflections when peering into the mirror blank.

Step 8:

We need to make another tool for this operation. You can make such a device from plaster or thick plywood. She will be covered soft material- resin.

Resin coniferous trees– very sticky and difficult to clean off.

Make another cylinder around the base of the jig. Melt a large amount of resin and pour it into the cylinder. Allow the resin to cool and remove the cardboard casing. After this, we will begin to form the surface; it is necessary to give it a slight convexity. The created channels will also help you when processing glass.

Step 9: Polish

Place some wet cerium powder on the resin and start rubbing the mirror against it. Cerium will penetrate the surface of the resin. Use soapy lubricant if necessary.

Step 10: Making a Foucault Tester

Foucault tester is a tool designed to analyze the surface of parabolic mirrors. It has a light source that shines onto the mirror. When the light returns, it is focused in a different area (if it came from the edge or center of the mirror).

The tester uses this principle to allow you to visually see errors as small as 1 millionth of a cm. By adding a Ronchi screen to the tester you will save time because you will get an idea of ​​the surface without any measurements.

To make life easier, make a mirror stand. A screw at the back allows you to adjust the angle.

Step 11: Making a paraboloid

After the finishing stage, we should have a fully polished mirror with a beautiful spherical surface. However, the sphere is not suitable for astronomical purposes. We must get a paraboloid.

The difference between a sphere and a paraboloid is small (about 1 micron). To achieve this difference we will use a Foucault test. Since we know what the reflection should look like, we will do special finishing with cerium oxide until the reflection on the mirror matches the theoretical one.

The appearance of the grind will resemble a "W". The amplitude should be 4/5 of the diameter in the transverse and longitudinal direction.

There is also a comprehensive list of different techniques to correct errors on a specific surface.

Step 12: Surface Testing Using a Foucault Tester

This is what the reflection looks like in a Foucault tester equipped with a Ronchi grid.

Depending on the case (the mesh cuts the light before or after the radius of curvature), the lines can be interpreted and the shape of the surface can be deduced.

The Couder mask is used for measurements with a Foucault tester.

Step 14: Aluminizing

In order to completely complete the craft, it needs to be sent for aluminization. Currently, the mirror reflects only 4% of the light. Aluminum contribution to the surface will increase the percentage by more than 90%.

An optional addition - a SiO2 coating will help protect the metal from any source of oxidation.

You can add a center imprint - this helps with collimation and does not affect the quality of the mirror, since the center does not participate in the formation of the image that you will see in the eyepiece.

To be continued…

This article is intended for those amateur astronomers who have already played with binoculars and a refracting telescope, looked at the phases of Venus, the rings of Saturn and the moons of Jupiter, and want something less boring and more stunning. For example, 1000x with a huge lens. It is impossible to do this with lenses alone: ​​they produce so-called chromatic aberration, which manifests itself in the form of rainbow halos around objects, the stronger the stronger the magnification of the telescope.

Therefore, the task arises of assembling a homemade reflecting telescope, that is, a telescope on mirrors. In his simplest form it consists of two mirrors (lens and diagonal) and one eyepiece lens.

Where to get it

The main mirror-lens of a reflecting telescope is its most important and critical part. And it is also the most difficult to manufacture. Finding a ready-made mirror of this type is almost impossible.

Although there is one way: you can make this from a concave or convex-concave lens. Find the concave or convex-concave lens of the most big size whatever you can find. It is important that the focal length be as high as possible, and, therefore, the concavity as small as possible: from too powerful concave lenses, not a spherical, but a parabolic shape is required, and this is a completely different deficiency that cannot be improvised in any way.

The most reliable calculation is to find a plano-concave one with a diameter of 10-12 cm and an optical power of 1 diopter. Look for it in optical stores. Thus, a homemade telescope of 1000x will not work, but you can do something with it.

Silver plating using chemistry

Then you need to do silvering to get a mirror. Prepare a solution called Tollens' reagent. In order to prepare this reagent, you need: silver nitrate (lapis), caustic soda ( caustic soda) and ammonia solution.

This reagent kit also includes formaldehyde (formaldehyde solution). Dissolve 1 g of silver nitrate in 10 ml of water, and 1 g of sodium hydroxide in another 10 ml of water. Mix these solutions, a white precipitate should form. Add ammonia solution until the precipitate dissolves. This solution is Tollens' reagent.

To use it for silvering, you should pour it into the concave part, which has previously been thoroughly cleaned of any contaminants. If the concavity is very weak, you should make a barrier of wax or plasticine along its edge.

Having poured the reagent, you should begin to add formaldehyde to it in frequent drops. Soon a film of silver will form and it will turn into a concave mirror. Keep in mind that Tollens' reagent does not have a long shelf life; it must be used immediately after it is prepared.

There are also ways to make a concave surface yourself, first of all - grinding the concave surface on glass circles. However, these methods are too complicated and are not recommended for use by beginners.

A diagonal mirror should be made in the same way as a concave one. It should be perfectly straight; For its manufacture, the flat side of any plano-convex or plano-concave is suitable.

Telescope assembly

Now you can start assembling your homemade one. You will need a tube exactly the length of the focal length (if you used a 1 diopter plano-concave lens for manufacturing, then take a tube 100 cm long, +0.5-1 cm adjustment for thickness).

The pipe should be open at one end and closed at the other, and painted inside with the blackest paint you can find. The diameter of the pipe should be 1.25 times the diameter of the refractor mirror; if you used a lens with a diameter of 100 mm to make it, take a pipe with a diameter of 125 mm.

Attach the lens mirror to the bottom of the pipe, exactly in the center. To make it convenient to do this, it is better to provide a removable bottom. You can attach the lens to the bottom, for example, with superglue.

Make a hole closer to the open end of the pipe. To calculate the desired position for the hole, measure its radius from the open end of the pipe. This is where the center of the hole should be. The eyepiece will be fixed in this hole (perpendicular to the pipe).

It should hang on the optical axis at an angle of 45 degrees. If the angle is maintained correctly, then when you look through the eyepiece you will see the image. If you don't succeed the first time, experiment with the angle.

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

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

The very name of the device – solar concentrator – speaks for itself. This device receives the sun's rays and collects them into a single energy beam. The simplest concentrator is familiar to everyone from childhood. This is an ordinary biconvex lens, which could be used to burn out various figures, inscriptions, even entire pictures, when the sun's rays were collected by such a lens into a small point on wooden board, 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 used very little in practice, since they have large sizes. Their use is justified where the dimensions of the concentrator are not critical.

Refractor Solar Concentrator

The prism solar radiation concentrator does not have 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 back face reflects it, and radiation comes out of the side face. The operation of such a device is based on the principle of complete internal reflection rays before they hit the side face of the prism.

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

Parabolic (reflective) 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 various ways. You can heat water using 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 oven for cooking.

Parabolic concentrator as a solar oven

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

The simplest scheme for heating water with a solar concentrator

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

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

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

How to make your own solar concentrator

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

In order for the film to lay flat, without wrinkles or folds, it should be cut into strips no more than 3 to 5 centimeters wide. If you intend to use the concentrator as a solar oven, it is recommended to cut a hole with a diameter of approximately 5–7 centimeters in the center of the plate. A bracket with a stand for dishes (burner) will be passed through this hole. This will ensure that the container with the food you are preparing does not move when the reflector is turned towards the sun.

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

Homemade solar concentrator - oven

To determine the focal point, you need to arm yourself with dark glasses, a wooden plank and thick gloves. Then you need to point the mirror directly at the sun, catch a sun bunny on the board and, moving the board closer or further relative to the mirror, find the point where this bunny will have minimum dimensions- a small point. Gloves are needed to protect your hands from being burned if they accidentally fall into the area of ​​the beam. Well, when the focal point is found, all that remains is to fix it and install the necessary equipment.

Options self-made There are many solar concentrators. In the same way, you can make a Stirling engine yourself from scrap materials. And this engine can be used for a variety of purposes. How much imagination, desire and patience is enough?

Do-it-yourself/DIY

Parabolic mirror for a reflecting telescope using homemade CNC machine

Have you seen how much a reflector with a mirror with a diameter of 18 inches (almost 46 cm) now costs?
Therefore, my park of crazy engineering ideas is replenished with a new item!

To create a mirror, we will need a lot of plexiglass or non-fragile (so-called viscous) glass. To select the material, you have to think hard, yes. You will also need three or four powerful and accurate servos with controllers, Arduino and silent radio components. Next, you need material for the bed, machine body and rotating parts. Well, and most importantly - hand cutter, suitable for processing the selected material.

The idea is to use a cutter mounted on a rotating rod to create concentric grooves of decreasing radius and increasing depth with each new circle. Thus, we obtain a stepped surface close to a paraboloid of revolution, because all changes in the position of the cutter and the depth of its immersion will be calculated using a parabolic function. Next, the surface is coated with epoxy resin and, with the help of rapid rotation of the workpiece, it is evenly distributed over the surface, filling the “steps” and bringing the surface as close as possible to a paraboloid.

The main problems that I will definitely encounter are:

• Positioning accuracy
• The choice of material and cutter, in the case of glass there will be chips, and plexiglass is too soft and does not hold its shape
• The hassle of “puttying” the steps with epoxy and final sanding
• Applying a reflective layer. (dusty, yeah)

People have been using a huge amount of free energy from the sun, water and wind and much more that nature can provide for a long time. For some, this is a hobby, while others cannot survive without devices that can extract energy “out of thin air.” For example, in African countries, solar panels have long become a life-saving companion for people; solar-powered irrigation systems are being introduced in arid villages, “solar” pumps are being installed on wells, etc.

IN European countries the sun does not shine so brightly, but summer is quite hot, and it is a pity when the free energy of nature is wasted. There are successful designs of solar-powered ovens, but they use solid or prefabricated mirrors. Firstly, this is expensive, and secondly, it makes the structure heavier and therefore not always convenient to use, for example, when a light weight of the finished concentrator is required.
An interesting model of a homemade parabolic solar concentrator was created by a talented inventor.
It does not require mirrors, so it is very light and will not be a heavy load on a hike.

To create a homemade solar concentrator based on film, very few things are required. All of them are sold at any clothing market.
1. Self-adhesive mirror film. It has a smooth, shiny surface and is therefore an excellent material for the mirror part of a solar oven.
2. Chipboard sheet and a sheet of hardboard of the same size.
3. Thin hose and sealant.

How to make a solar oven?

First, two rings are cut out from a chipboard of the size you need using a jigsaw, which must be glued to each other. There is one ring in the photo and video, but the author indicates that he later added a second ring. According to him, it would have been possible to limit ourselves to one, but the space had to be increased to form a sufficient concavity of the parabolic mirror. Otherwise the beam focus will be too far away. A circle of hardboard is cut to the size of the ring to form the back wall of the solar concentrator.
The ring should be glued to the hardboard. Be sure to seal everything well with sealant. The structure must be completely sealed.
Carefully make a small hole on the side so that there are even edges, into which tightly insert a thin hose. To ensure a tight seal, the connection between the hose and the ring can also be treated with sealant.
Stretch a mirror film over the ring.
Pump out the air from the installation body and thus form a spherical mirror. Bend the hose and clamp it with a clothespin.
Make a convenient stand for the finished concentrator. The energy of this installation is enough to melt an aluminum can.

Attention! Parabolic solar reflectors can be dangerous and can cause burns and eye damage if not handled carefully!
Watch the manufacturing process solar stove on video.

Material used from the site zabatsay.ru. How to make a solar battery - .