Dish antenna as parabolic mirror for OPTICAL telescope? 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.
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".)