- #1
swampwiz
- 571
- 83
Are the profiles of the reflecting/refracting surfaces spherical for the bleeding-edge astronomical instruments?
I realize that because of the paraxial approximation, a "small angle" for a "ray" of light on spherical reflecting & refracting surfaces allows for a clean focus to take place. However, even a very small angle yields some spherical aberration, so I wonder that since astronomical instruments are always focused on infinity (or something so far that the error in presuming infinity is orders of magnitude less than an spherical aberration), the surfaces are tightly designed as a paraboloid - or at least all the surfaces are carefully designed to have the net effect of true focus that is not dependent on the spherical aberration to avoid blur.
I realize that because of the paraxial approximation, a "small angle" for a "ray" of light on spherical reflecting & refracting surfaces allows for a clean focus to take place. However, even a very small angle yields some spherical aberration, so I wonder that since astronomical instruments are always focused on infinity (or something so far that the error in presuming infinity is orders of magnitude less than an spherical aberration), the surfaces are tightly designed as a paraboloid - or at least all the surfaces are carefully designed to have the net effect of true focus that is not dependent on the spherical aberration to avoid blur.