Quote:
Originally Posted by Peter Ward
I knew I had read something on this in Sky & Tel. With a little digging I found this
http://home.freeuk.com/m.gavin/flux.htm
The author quaintly puts the airy disk size or "circle of confusion" at around 5mm....this is several orders of magnitude worse than a diffraction limited
glass mirror  |
Also, the owner of the telescope with mylar mirror must be VERY quiet when using it - electrostatic microphones are designed around a mylar membrane, which moves as acoustic waves are hitting a membrane surface. Electrical signal is picked up as variation of capacitance between membrane and back plate.
Another example is something from James Bond movies, but also from real world: laser microphone.. Laser beam reflected from glass window is modulated by the sounds produced inside the room.
Nobody wants telescope mirror shape to be sensitive to sounds, and this is exactly what is happening with thin membranes....