In my distant childhood, I came across a textbook on astronomy from those even more distant years, which I did not find when this astronomy was a subject at school. I read it thoroughly and dreamed of a telescope so that I could look into the night sky with at least one eye, but it didn’t work out. I grew up in a village where there was neither knowledge nor a mentor for this. And so this passion went away. But with age I discovered that the desire remained. I've scoured the Internet and it turns out there are a ton of people who are passionate about telescope building and assembling telescopes, and what kind of telescopes too, and from scratch. I gathered information and theory from specialized forums and decided to build a small telescope for a beginner.
If you had asked me earlier what a telescope is, I would have said - a tube, you look from one side, and point the other at the object of observation, in a word, a telescope, but larger in size. But it turns out that for telescope construction they mainly use a different design, which is also called a Newtonian telescope. Despite its many advantages, it does not have many disadvantages compared to other telescope designs. The principle of its operation is clear from the figure - the light of distant planets falls on a mirror, which ideally has a parabolic shape, then the light is focused and carried outside the pipe using a second mirror, installed at 45 degrees relative to the axis, diagonally, which is called - diagonal. Then the light enters the eyepiece and into the eye of the observer. 
A telescope is a precision optical instrument, so care must be taken during manufacturing. Before this, it is necessary to make calculations of the structure and installation locations of the elements. There are online calculators calculating telescopes and it would be a shame not to take advantage of this, but it doesn’t hurt to know the basics of optics either. I liked the calculator.
To make a telescope, in principle, nothing supernatural is needed; I think that any business person in the utility room has a small lathe for at least wood, or even metal. And if there is also a milling machine, I envy you with white envy. And it’s not at all uncommon now to have home CNC laser machines for cutting plywood and a 3D printing machine. Unfortunately, in my household I have nothing of all of the above, except a hammer, drill, hacksaw, jigsaw, vice and small hand tools, plus a bunch of cans, trays with a scattering of tubes, bolts, nuts, washers and other garage scrap metal, which seems like it should be thrown out, but it’s a pity.
When choosing the size of the mirror (diameter 114mm), it seems to me that I chose the golden mean: on the one hand, this size of the chassis is no longer quite small, on the other hand, the cost is not so huge that in case of a fatal failure I would suffer financially. Moreover, the main task was to touch, understand and learn from mistakes. Although, as they say on all forums, the best telescope is the one in which you observe.
And so, for my first, I hope not the last, telescope, I chose a spherical main mirror with a diameter of 114 mm and aluminum coating, 900mm focus and diagonal mirror, shaped like an oval with a small diagonal of one inch. With these mirror sizes and focal lengths, the differences between the shapes of a sphere and a parabola are negligible, so an inexpensive spherical mirror can be used.
According to Navashin’s book, Telescope of an Amateur Astronomer (1979), the internal diameter of the pipe for such a mirror must be at least 130 mm. Of course, more is better. You can make the pipe yourself from paper and epoxy, or from tin, but it would be a sin not to use ready-made cheap material - this time a meter-long PVH sewer pipe DN160, bought for 4.46 euros in a hardware store. The wall thickness of 4mm seemed sufficient to me in terms of strength. Easy to saw and process. Although there is one with a 6mm wall thickness, it seemed a bit heavy to me. In order to saw it, I had to brutally sit on it; no residual deformations were visible to the eye. Of course, aesthetes will say fi, how can you look into the stars through a pipe for an Aries. But for real hands-on priests this is not an obstacle.
Here she is, beauty
Knowing the parameters of the mirror, you can calculate the telescope using the above-mentioned calculator. Not everything is clear right away, but as creation progresses, everything falls into place; the main thing, as always, is not to get hung up on theory, but to combine it with practice.
Where to begin? I started, in my opinion, with the most difficult one - the diagonal mirror mounting assembly. As I already wrote, the manufacture of a telescope requires precision, but that does not negate the possibility of adjusting the position of the same diagonal mirror. Without fine adjustment - nothing. There are several mounting schemes for a diagonal mirror: on one stand, on three stretchers, on four, and others. Each has its own pros and cons. Since the dimensions and weight of my diagonal mirror, and therefore its mounting, frankly speaking, are small, I chose a three-beam mounting system. As stretch marks I used a found stainless steel adjustment sheet 0.2mm thick. As fittings I used copper couplings for a 22mm pipe with an outer diameter of 24mm, slightly smaller than the size of my diagonal, as well as an M5 bolt and M3 bolts. The central M5 bolt has a conical head, which, inserted into the M8 washer, acts as a ball joint, and allows you to tilt the diagonal mirror with the M3 adjusting bolts when adjusting. First I soldered the washer, then roughly cut it at an angle and adjusted it to 45 degrees on a sheet of coarse sandpaper. Both parts (one completely filled, the second 5mm through the hole) took less than 14 ml of five-minute two-component epoxy adhesive Moment. Since the dimensions of the unit are small, it is very difficult to place everything and for it all to work properly, the adjustment arm is not enough. But it turned out very, very well, the diagonal mirror is adjusted quite smoothly. I dipped the bolts and nuts into hot wax to prevent the resin from sticking when pouring. Only after the production of this unit did I order the mirrors. The diagonal mirror itself was glued to double-sided foam tape. 
Below the spoiler are some photos of this process.
Diagonal Mirror Assembly
The manipulations with the pipe were as follows: I sawed off the excess, and since the pipe has a larger diameter socket, I used it to strengthen the area where the diagonal braces are attached. I cut out the ring and put it on the pipe using epoxy. Although the rigidity of the pipe is sufficient, in my opinion it would not be superfluous. Then, as the components arrived, I drilled and cut holes in it, and glued it on the outside decorative film. Very important point- painting the pipe from the inside. It should be such that it absorbs as much light as possible. Unfortunately, the paints on sale, even matte ones, are not suitable at all. There is a special There are paints for this, but they are expensive. I did this - following the advice from one forum, I covered the inside with paint from a can, then poured rye flour into the pipe, covered the two ends with film, twisted it well - shook it, shook out what didn’t stick and blew the paint out again. It turned out very well, you look like you’re looking into a chimney.
The main mirror mount was made from two 12mm thick plywood disks. One with a pipe diameter of 152mm, the second with a main mirror diameter of 114mm. The mirror rests on three circles of leather glued to the disk. The main thing is that the mirror is not tightly clamped; I screwed the corners and wrapped them with electrical tape. The mirror itself is held in place by straps. The two discs are able to move relative to each other to adjust the main mirror using three M6 adjusting bolts with springs and three locking bolts, also M6. According to the rules, the disks must have holes to cool the mirror. But since my telescope will not be stored at home (it will be in the garage), temperature equalization is not relevant. In this case, the second disk also plays the role of a dust-proof back cover.
In the photo the mount already has a mirror, but without the rear disc. 
Photo of the manufacturing process itself.
Mounting the main mirror
I used a Dobson mount as a support. There are a lot of different modifications on the Internet, depending on the availability of tools and materials. It consists of three parts, the first in which the telescope tube itself is clamped -
The orange circles are sawn-off round timber pipes into which circles of 18mm plywood are inserted and filled epoxy resin. It turned out component sliding bearing.
The second one, where the first one is placed, allows the telescope tube to move vertically. And the third is a circle with an axis and legs, on which a second part is placed, allowing it to be rotated.
Pieces of Teflon are screwed into the places where the parts rest, allowing the parts to be moved relative to each other easily and without jerking.
After assembly and primitive setup, the first tests were completed. 
A problem immediately appeared. I ignored advice smart people Do not drill holes for mounting the main mirror without testing. It’s good that I sawed the pipe with a reserve. The focal length of the mirror turned out to be not 900mm, but about 930mm. I had to drill new holes (the old ones were sealed with electrical tape) and move the main mirror further. I just couldn’t catch anything in focus; I had to lift the eyepiece itself from the focuser. The disadvantage of this solution is that the fastening and adjusting bolts at the end are not hidden in the pipe. but they stick out. In principle, it is not a tragedy.
I filmed it with my cell phone. At that time there was only one 6mm eyepiece, the degree of magnification was the ratio of the focal lengths of the mirror and the eyepiece. IN in this case it turns out 930/6=155 times.
Test number 1. 1 km to the object. 
Number two. 3km. 
The main result has been achieved - the telescope is working. It is clear that to observe the planets and the Moon, better alignment is needed. A collimator was ordered for it, as well as another 20mm eyepiece, and a filter for the Moon on a full moon. After that, all the elements were removed from the pipe and put back more carefully, more firmly and more accurately.
And finally, the purpose of all this is observation. Unfortunately, there were practically no starry nights in November. Of the objects that I managed to observe, only two were the Moon and Jupiter. The moon does not look like a disk, but rather a majestically floating landscape. With a 6mm eyepiece, only part of it fits. And Jupiter with its satellites is simply a fairy tale, taking into account the distance that separates us. It looks like a striped ball with satellite stars on the line. It is impossible to distinguish the colors of these lines; here you need a telescope with another mirror. But it’s still fascinating. To photograph objects you need both optional equipment, and another type of telescope - high-aperture with a short focal length. Therefore, here are only photos from the Internet that accurately illustrate what is visible with such a telescope. 
Unfortunately, you will have to wait until spring to observe Saturn, but for now Mars and Venus are in the near future.
It is clear that mirrors are not the only cost of construction. Here is a list of what was purchased besides this.
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 things he invented optical devices 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 concentrator solar radiation, which collected the sun's rays into one energy beam. And at the focus of this concentrator, the temperature could reach 300°C - 400°C, which is quite enough to ignite the wooden ships of the Roman fleet. One can only guess what kind of device Archimedes invented, although, according to modern ideas, he had only two options.
The very name of the device – 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 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 total internal reflection of rays before they hit the side edge prisms.
Unlike refractor concentrators, reflective concentrators work on the principle of collecting reflected sunlight into an energy beam. According to their design, they are divided into flat, parabolic and parabolic-cylindrical concentrators. If we talk about the effectiveness of each of these types, then the highest degree of concentration - up to 10,000 - is provided by parabolic concentrators. But to build systems solar heating Mostly 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 solar oven for cooking food.
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 a coolant placed at the focus will allow you to quickly heat even running water, which can then be used for household purposes, for example, for showering, washing dishes.
The simplest scheme for heating water with a solar concentrator
If 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. At the inverter output - standard voltage 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 the reception and concentration of the maximum amount of solar energy. For individual use, it is unlikely to 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 old plate from a 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?
About how to build 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 solar energy, and its parabolic shape concentrates this energy at one point. This installation will work effectively in most regions of Russia, up to 65 degrees north latitude.
To assemble the collector, we need several basic things: the antenna itself, the sun tracking system and the heat exchanger-collector.
Parabolic antenna.
You can use any antenna - iron, plastic or fiberglass. The antenna should be a panel type, not a grid type. The antenna area and shape are important here. We must remember that 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 power assembled antenna with a mirror area of 3 m.
You will also need a rotating mechanism for the antenna assembly. It can be ordered on Ebay or Aliexpress.
You will need a roll of aluminum foil or Mylar mirror film used for greenhouses. Glue that will stick the film to the parabola.
Copper tube with a diameter of 6 mm. Fittings, for connection hot water to the tank, to the pool, or wherever you will use this design. Swivel mechanism The author purchased tracking on EBAY for $30.
Step 1 Modify the antenna to focus solar radiation instead of radio waves.
You just need to attach the Mylar mirror film or aluminum foil to the antenna mirror.
You can order such a film on Aliexpress, if you suddenly don’t find it in stores
It's almost as easy to do as it sounds. You just need to take into account that if the antenna, for example, has a diameter of 2.5 m and the film is 1 m wide, then there is no need to cover the antenna with film in two passes; folds and irregularities will form, which will worsen the focusing of solar energy. Cut it into small strips and attach it to the antenna with glue. Make sure the antenna is clean before applying the film. If there are places where the paint is swollen, clean them sandpaper. You need to smooth out all the unevenness. Please note that the LNB converter is removed from its place, otherwise it may melt. After sticking the film and installing the antenna in place, do not bring your hands or face close to the place where the head is attached; you risk getting serious sunburn.
Step 2 tracking system.
As was written above, the author bought a tracking system on Ebay. You can also look for rotating sun tracking systems. But I found a simple circuit for a pretty penny price that tracks the position of the sun quite accurately.
Parts List:
(downloads: 428)
* U1/U2 - LM339
*Q1 - TIP42C
*Q2 - TIP41C
* Q3 - 2N3906
* Q4 - 2N3904
* R1 - 1meg
* R2 - 1k
* R3 - 10k
* R4 - 10k
* R5 - 10k
* R6 - 4.7k
* R7 - 2.7k
* C1 - 10n ceramic
* M - DC motor up to 1A
*LEDs - 5mm 563nm
Video of the solar tracker working according to the scheme from the archive
You can make it yourself based on the front hub of a VAZ car.
For those interested, the photo was taken from here:
Step 3 Creating a heat exchanger-collector
To make a heat exchanger, you will need a copper tube, rolled into a ring and placed at the focus of our concentrator. But first we need to know the size of the dish's focal point. To do this, you need to remove the LNB converter from the plate, leaving the converter mounting posts. Now you need to turn the plate in the sun, having first secured 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 this, turn the antenna away from the sun and remove the board from the mount. All manipulations with the antenna, its reversals, are carried out so that you do not accidentally put your hand into the focus of the mirror - this is dangerous, you can get seriously burned. Let it cool down. Measure the size of the burned piece of wood - this will be the size of your heat exchanger.
The size of the focus point will determine how much copper tube you will need. The author needed 6 meters of pipe with a spot size of 13 cm.
I think that perhaps, instead of a rolled up tube, you can put a radiator from a car heater; there are quite small radiators. The radiator should be blackened for better heat absorption. If you decide to use a tube, you must try to bend it without kinks or kinks. Usually, for this purpose, the tube is filled with sand, closed on both sides and bent on some mandrel of a suitable diameter. The author poured water into the tube and put it in freezer, with the open ends facing up to prevent water from leaking out. The ice in the tube will create pressure from the inside, which will avoid kinks. This will allow the pipe to be bent with a smaller bend radius. It must be rolled into a cone; each turn should be slightly larger in diameter than the previous one. You can solder the collector turns together for a more rigid structure. And don't forget to drain the water after you're done with the manifold so you don't get scalded by steam or hot water after you put it back in place.
Step 4. Putting everything together and trying it out.
You now have a mirror parabola, sun tracking module, placed in a waterproof container, or plastic container, complete collector. All that remains to be done is to install the collector in place and test it in operation. You can go further and improve the design by making something like a pan with insulation and putting it on the back of the manifold. The tracking mechanism must track movement from east to west, i.e. turn towards the sun during the day. And the seasonal positions of the luminary (up/down) can be adjusted manually once a week. You can, of course, add a tracking mechanism vertically - then you will get almost automatic operation installations. If you plan to use the water to heat a pool or as hot water in the water supply, you will need a pump that will pump water through the collector. If you heat a container of water, you must take measures to avoid the water boiling and the tank exploding. This can be done using
I have a simple Celestron PowerSeeker 127 EQ telescope, the one pictured above. My wife gave it to me for my birthday. It was a rather spontaneous gift like this: “I don’t know what to give you, oh look at the store, let’s go in and have a look.” In principle, I was very glad to receive such a gift; it was a very interesting thing. However, while using it, I realized that I wanted more. This PowerSeeker 127EQ telescope has a number of significant design flaws that, due to my inexperience, I simply did not realize. The main disadvantage is the spherical main mirror and the corrective lens for it. As a result, an overcomplicated optical design, inaccurate fitting of the corrective lens, which is also not High Quality. In general, I think the quality of the observed image with such a mirror diameter could have been better.
I started thinking that I needed a different telescope. This is a normal situation. They say that no matter what kind of telescope an amateur has, he always dreams of the best. And then the question arises: buy or make it yourself? The answer is actually not obvious. It's probably easier to buy, and maybe even cheaper? Building it yourself in the absence of experience is a difficult technical task; it is not known whether it will work at all and it is not clear whether it will be cheaper than just buying.
I entered the slippery path of independent telescope construction. Next, I’ll tell you about my first steps in this direction, but I warn you right away that don’t expect to read an article with a happy ending just yet. I am very far from it (if it happens at all).
So, you need to start by studying the theory.
In my opinion, there is nothing better than the book “Telescopes for Astronomy Lovers”, L.L. Sikoruk, 1982. Despite the fact that the book is over thirty years old, I have never seen a more detailed presentation “from start to finish.” There is also a book by M. S. Navashin, “The Amateur Astronomer’s Telescope,” 1979. Also useful.
Besides these very useful books Of course, you can and should visit astroforums. for example, this one. Here you can ask a question and read about who does what and how.
Last refuge: youtube.com. It may seem strange, but many people around the world are building telescopes. Some even have video blogs and show the manufacturing process. Keywords to search on YouTube: mirror grinding.
In general, I would say that the niche of amateur telescope construction in Russia seems completely empty (but this is not certain). In Europe and America there are special stores that sell mirror blanks, grinding powders, and tools and kits for making mirrors (teleskope mirror kit).
Now, of course, it’s not ’79 or ’82, but where can I get a blank for a telescope mirror? Or where can I get sanding 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 mirror blank - a disk with a diameter of 200 millimeters and they told me that it would cost about thirty thousand without postage. Perhaps there is very high-quality optical glass, but I, an amateur, simply don’t understand (without irony, I know that somewhere exceptional quality may be required).
To tell the truth, for thirty thousand you can already have it ready large mirror buy somewhere in great China.
In general, I decided to make it from scrap materials, as Sikoruk advised to do in his book. The material at hand is display glass (but not tempered). I need to cut several disks of glass 10 millimeters thick and then glue them together liquid glass. In his book, Sikoruk writes and justifies the required thickness of the main mirror depending on its diameter.
The first epic. Cutting a glass blank
I went to a glazier and asked him to cut me rectangular pieces of 10 mm glass approximately 250x250 millimeters, but they all had to be from the same sheet in order to be sure of the same properties of all the pieces.
Went to the store and bought a pair aluminum pans internal diameter 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 with it, but no, we are smart, we make 180 at once.
The pan was sawn and a weight and two protruding bolts were screwed to the bottom.
This will be a cutter.
Next comes the long and painful process of making a machine for cutting out the workpiece. This is where the engine from the old one comes in handy. washing machine, some kind of pulley from her old gearbox, pieces of plywood, studs, nuts and other nonsense.
Overall it looks like this:
The lid of the pan is glued to the glass with silicone and its edges are chamfered. It serves as a centering element for my cutter. The cutter, that is, half a pan, is put on top and driven by a gearbox from the motor.
This thing works like this (my video):
While working, you need to constantly add abrasive under the edges of the cutter. I worked with the abrasive for about five to seven minutes, the abrasive was worn out and mixed with glass and aluminum crumbs. Wash off the old abrasive and apply 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 added new abrasive with a spoon.
Not really Good photo, but you can see how much the “cutter” has sunk into the thickness of the glass:
I extracted 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.
I hit the resulting pieces with a hammer, collected the crumbs in a jar - the result was a coarse abrasive powder. Of course, at this stage such savagery is still acceptable, but then we will have to improve production standards.
As a result, one 180 mm disk from a 10 mm sheet is cut on my machine in about three to three and a half hours. I cut four disks:
My wealth:
According to my plan, I will glue them together in pairs with liquid glass, treat the edges with epoxy, as Sikoruk advises, and I will have two 180 mm blanks of the main mirror. Next I'll start sharpening them and probably ruin one. Well, the second one, I hope it works out.
I have already purchased a set of sanding powders for this mission:
But then another story begins. Needs sharpening. This is done in several stages: rough molding-grinding, grinding and then polishing. I'm honestly stuck at this point. Here are some illustrations from the book “Telescopes for Astronomy Lovers”:
Ripping:
Grinding:
Typical mistakes:
Unfortunately, despite detailed explanations in Sikoruk's book and from other sources, I do not have an absolutely accurate idea of how to do this correctly. The problem is that you need to perform a parabola with very high accuracy: Errors, bumps or pits on the main mirror should be less than 1/8 of the wavelength of light. The accuracy of the parabola must be at least 0.05 microns.
Here's what Sikoruk writes in his book:
The process of figuration and shadow testing is difficult to divide into components - it is a single creative process, where decisive role Often not only knowledge, but also intuition plays a 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 figuration, although, there is no doubt, the sight of a completely flat shadow picture is a stunning sight.In the polishing process, according to J. Mattewson, “there is always an element of mysticism.” This is partly due to the fact that the polishing process is largely insufficiently studied, but partly because the master himself often wants a little mysticism, when figuration ceases to be just a technology, but becomes largely an art. It’s not for nothing that D. D. Maksutov said that the optician prefers to “conjure” over homemade polishing pad resin, not trusting factory resin. (True, if you have the opportunity to purchase factory polishing resin, you should do it). Often the success of a business is determined 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.
It turns out that apparently there are no clear methods by which to act in order to obtain a true parabola?
In fact, of course, the same book by Sikoruk tells how to control the shape of a 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 zonal errors, but it is absolutely not clear how to modify the polishing pad so that the zonal errors are corrected during further polishing.
I watched a lot of video demonstrations on YouTube: there is molding and sanding 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 machining mirrors:
From all this it turns out that everyone does as they come up with, but how to do it in such a way as to guarantee the result? There is something to think about...
After quite a lot of thought, I decided that before sharpening I should try to make a software model of the entire grinding process. For some reason it seemed to me that this would be quite easy to do. I thought that I would make a sanding machine, something like the one in the last video.
The mirror blank should rotate slowly at the bottom, and at the top, for example, a steel stripping ring will move in a reciprocating motion using a crank mechanism.
I decided that the software model could be very simple: I need to calculate the time spent by each point of the mirror workpiece under the surface of the stripping ring. You can try to count not the entire surface of the workpiece, but only one cut-radius.
This video is made from pictures of the virtual peeling process in my program:
I thought that by selecting the length of the stroke in the software model, the length of the arms of the crank mechanism (and its movement is far from a sinusoid), I would be able to tell exactly how to sharpen in order to reach a parabola.
Unfortunately, I must say that the further I delve into the problem, the more I realize that my virtual software 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 the rubbing parts, but it is different in the center and at the edges. Then I do not yet take into account the pressure of the peeling ring on the workpiece, but this apparently needs to be done, since during the work the shape of the workpiece changes, which means the distribution of friction forces on the surface of the workpiece also changes.
When I wrote this article, I even thought of giving the entire source code of my program (C/C++) here, however, what’s the point if the program doesn’t work?
I am currently engaged in a radical rewrite of my software and still intends to make a software model of the mirror figuration process. Perhaps, if I succeed, I will publish my code.
I finally picked up a vacuum manifold for 20 tubes and will use them to assemble a concentrator. 1 tube filled with water (3 liters) heated up from 20*C to 68.3*C (boiling water to the touch) in 2 hours 40 minutes. Outside the window on May 26, in the sun 42 * C in the shade 15 * C, the time of the experiment is from 16.27 to 18.50, the sun is setting...
And in the concentrator the measurement showed 19 minutes! up to the same 68*C. The speed can be increased by increasing the area of the concentrator, but then the windage increases and the integrity of the structure deteriorates...
The concentrator area is 1.0664 sq.m. (62x172 cm.)
Focal length 16cm.
You buy 1 vacuum tube, and remove it like 7 in my version, if you count by area. Below is a video of one of the pioneers who inspired me to my feat.
So far I have encountered the problem of poor gluing of acrylic with glue for mirrors. It peeled off easily from the base... Also, the glue for mirrors is very soft and the system “walks”, the structure needs to be strengthened.
said):
As advised by FarSeer; I placed the axis horizontally (east-west orientation for winter). This arrangement is simpler in terms of design, wind loads are less, and removal (inversion) from precipitation is also easier.
Due to the fact that I will place my “scoops” horizontally in the east-west direction, so as not to get stuck on the trackers, I had to think about how to make heat extraction more efficient, since the standard scheme with liquid condensation may not work in theory, so as there is no condensate flowing down and, accordingly, steam rising upward to release its heat. I made 2 types of heat extraction from the vacuum tube.
Option-1 (on the right, in photo-1) The original tip (the thickening where steam collects) is actively washed by the coolant.
Option-2 (average, in photo-1) 2 tubes are taken, one 10mm. in diameter, the other 15 mm. in diameter and inserted into one another, by analogy with recuperators, the inner one does not reach the end a couple of cm. And the outer one is plugged at the end, and at the top these tubes are separated by a tee, see photo. As experiments have shown, between a horizontal tube and one standing at 45* at temperatures of about 80* the difference was about 5*, although I was told that in a horizontal position this tube would not work at all!
I’m waiting for warmer weather to dig holes for the posts, because the ground is still frozen and it’s not realistic to dig.
As for emergency modes, everything has already been thought out; there is a 1.5 kW Smart UPS with additional batteries.
The second and, in my opinion, the most significant point for solving emergency situations is covering the mirrors or concentrator from the sun or turning it away from the focus axis, which will bring the concentrator to minimum power A simple vacuum tube in the hottest season, for example, using the same principle, you can regulate the total power of the concentrators, removing some from the focus.For an option for a concentrator made from scrap material, see photo.
