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Can I use a chrome painted dish TV antenna as a parabolic reflector for my optical telescope? Given that glass mirrors are quite expensive, I am thinking of using a Dish TV antenna and coating its reflecting surface with chrome paint to give it a mirror finish. But I couldn't find any instance of it online. I did find several examples of people using a dish antenna for making an amateur radio telescope.

I was wondering if there is a reason why we can't use it in optical telescope.

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    $\begingroup$ You might look at something that's been painted with chrome paint and see if you can see anything. $\endgroup$
    – uhoh
    Oct 30, 2016 at 11:49
  • $\begingroup$ chrome paint? That must be some good paint. $\endgroup$ Jan 31, 2018 at 7:26
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    $\begingroup$ Not a scope, but I've heard they make a decent focusing element for a solar cooker. $\endgroup$ Jan 31, 2018 at 17:39
  • $\begingroup$ It might work as a solar oven, but a satellite dish is not going to make an optical image, ever, not even close. The active surfaces in an optical telescope need to be machined with a precision of 1 / 10000 of a mm or better. This will never happen with a regular satellite dish made for microwaves. $\endgroup$ Jan 31, 2018 at 19:51

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It's not possible I'm afraid.

Optical wavelengths (light) are typically of a wavelength under a micron, and an optical surface needs to be accurate to this level or better to be useful.

Radio wavelengths are typically 10-20cm or longer, and an adequate reflector can be made with surfaces accurate to a few centimetres (at a guess as I don't know the exact tolerance).

Also - I once experimented using a frequently mentioned substitute, a convex shaving mirror(!) as a reflecting telescope. Even that was so poor it was unusable at the lowest possible magnification.

(But it is possible to make your own reflector out of reasonably stable glass - it just won't be as big as a satellite dish! Search around for "Amateur telescope making".)

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I would have added this as a comment (not enough rep yet, I'm afraid)... To elaborate on Andy's answer, the first reason is that the surface of the satellite dishes are too coarse to form any kind of image. Polished optical surfaces are smoothed to a polish (generally much smoother than one would achieve in polishing a car, though).

Other problems come from the precision of the form - the paraboloid of the satellite dish may have errors on the order of millimeters, because radio waves (which satellites use) don't care about that much error. In fact, satellite dishes are EXACTLY the same as radio telescopes, except the receiver cone is designed for frequencies used by communication satellites instead of frequencies of interest to astronomy.

Just for your interest, old satellite dishes ARE well-suited to function as rough solar collectors (for a solar oven) or as an acoustic telescope (position a microphone or speaker where the receiver cone normally lies)!

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I think you should try. Sattelite dishes are made to collect very weak singals. And dish need to be aligned in millimeter range. And they are factory made with accuracy. start with 2ft parapolic offset dish which is much flat. i will try this also. In place of lnb you can fit mirror and it will reflect image to center of dish surface. Make a hole in center of dish surface and fit the eye peice lense to see.

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  • $\begingroup$ It's not going to work, at all, period. A barely acceptable optical telescope uses mirrors machined to a precision of 0.1 microns - that's 1 / 10000 of a milimeter. With a satellite dish you'd be very lucky to get within 1 mm of precison. Source: I make telescopes and telescope mirrors. $\endgroup$ Jan 31, 2018 at 19:47
  • $\begingroup$ 1/4 wavelength accuracy is about the minimum acceptable accuracy for an imaging mirror. For 400 nm light, That's "circular to within 100 nm". You don't get that by stamping steel. $\endgroup$ Feb 2, 2018 at 4:24
  • $\begingroup$ Lotta people use old tv dishes as radio telescopes. Never done it, but I hear it can be a rewarding hobby. $\endgroup$ Feb 2, 2018 at 4:28
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I believe anything is possible but it wwoukd take a lot of work and measurements. You can sand the Satelite dish first, using wet dry Sand paper. When you get to the fine portion. Use water with it. Then rubbing compound. Then it will be smoothe enough to work with. Use fiberglass at first to create the proper shape and hone it to a glass finish. Then one last addition before you add the refelective elements. That is to add epoxy and take down to the lowest measurement possible by honing it with a surface that fits the proper shape. Don't use paint but buy a crucible and melt aluminum and remove the slag, until it melts without any slag. Create a holder for the dish that will rotate and shift it in all directions. Pour the molten alumuminum in the dish and it will layer out. Make sure and wear ppersonal protective equipment. I would do 3 layers. After that polish it to a fine sheen and you will have your reflector. It is a lot of work but its worth doing if anything to prove it can be done. Ii don't believe in the answer it ccan't be done.then you can tell others how you did and almost. Took 6 months to accomplish. You will need to put this on a mount of your making and some serious counter weights. Get a uno, a bidorectional high tork motor,motorcyle or timing chain and create your own mount. Create an adjustble Equitorial plate and you can set it up on a permanent pillar Nd run it from inside. I am actually about to do the same.

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    $\begingroup$ You won't be able to freehand sand an optical parabolic surface. You have to go through the same process you would for a glass mirror. $\endgroup$ Aug 9 at 14:00
  • $\begingroup$ As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center. $\endgroup$
    – Community Bot
    Aug 9 at 15:42

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