Can i use a plexiglass concave mirror as a primary mirror on a telescope? will it be good as a glass mirror?

Answer 1

usually, glass mirrors are polished to achived a very precise final shape. I don't believe that technology exists for plexiglass. It probably could be done but is likely to be much more expensive than the traditional glass.

Answer 2

Absolutely not! Plexiglas has an enormous coefficient of thermal expansion. This means it is constantly changing shape as heat moves through it. A primary mirror must have a surface accurate to 1/4 the wavelength of the light you're trying to focus. You could never get it to the right shape because the heat generated by grinding would constantly change its shape while you're working it. Even if you could "magically" form it to the proper shape, plexiglas constantly squirms around due to the heat that always flows as it tries to equilibrate to its thermal environment.

Pyrex glass is the cheapest practical material for a primary mirror. It has a near-zero coefficient of thermal expansion and so is dimensionally stable. You can buy annealed Pyrex mirror blanks (unground) from Edmund Scientific Co. (I did, in 1963.) I imagine they're still in business and you can probably find them somewhere on the net.

Building your own reflecting telescope is a long and extremely painstaking job. Only obsessive perfectionists are likely to complete the project. Don't waste all that time and effort because you're too cheap to buy the right materials. On the other hand, building a big Newtonian telescope is an accomplishment of which you can be proud your entire life.

Good Luck.............

Answer 3

Plexiglas is not as thermally stable as glass. It grows too much with temperature change.