Does anyone know of an adjustable focusing mirror? Does anyone know of an adjustable focus mirror? Allowing short sight and long sighted people to see clearly in a mirror with no specs on. Is it even possible?
 A: Most of the glass telescope mirrors currently being manufactured are adaptive: they are made thin enough that their shape can be easily changed by piezoelectric actuators mounted underneath them. This allows almost instantaneous adjustment of their focal length across the mirror area that nulls out the effects of atmospheric distortion, moment by moment.
You can also do this in a cruder way by pulling a vacuum behind a metallized mylar film being used as a mirror. I recommend you buy a derelict snare drum shell, seal it to make it airtight, and mount an aluminized mylar sheet in place of the batter head and then carefully change the air pressure inside the drum shell to cause the film to draw in or bulge out slightly, while measuring the resulting focal lengths. Be sure to report your findings here!
A: The only adjustable optical component I know of is the lens in your eye. It changes focal length by being flexible. Muscles around the edge of the lens stretch it and change its shape.
As far as I know, all other lenses and mirrors are rigid. Their focal length is fixed.
Camera achieve a variable focal length in one of two ways. They have multiple lenses and adjust the separation between them. This is a zoom lens. Or they do it in software. The take an image with whatever focal length they have, and then adjust the pixels to zoom in.
In principal, you could do the same thing with mirrors. There are a few systems that have multiple mirrors. Large telescopes for example. Lasers for another. But these generally do not change the spacing between the mirrors.
For your application, use your phone. Zoom in if you want to see part of your face larger. Not ideal, but the best I can think of off hand.
