Aberrations Introduced by Prisms

Chromatic aberrations can be minimised in the best quality lenses by using two glasses of different refractive indices placed in contact so as to form a single lens. That way, any aberration introduced by the light passing through the first lens is cancelled out as it passes through the second. The process to create the lenses is not easy, and partly explains why the lenses used for brands of top quality camera equipment are inherently of high cash value.

Presumably the same method can be used in connection with prisms?

Isn't it what is done with Mirrors?

You make an excellent point. I think unfortunately most binoculars do use prisms to fold the optical path, and it is true that you will need one prism assembly (roof or Porro) to invert the image. But the path folding can be done with mirrors, and if the mirrors are reasonably flat they will not contribute the chromatic aberrations to the system the way a prism design would.

There are down sides to using mirrors to fold the optical path:

• You will need some ability to adjust the mirror alignments. Otherwise the left and right images will not have the same magnification and aspect ratios.
• you will need more folding because the optical path length in air will be ~1.5 times as long as it would be in glass.

If two prisms are identical and kept reversed, the aberrations created by one will be cancelled by the second. Various binoculars (and monoculars) in the market use this principle be they Porro type or roof prism type.

http://www.meade.com/support/selbinoc.html

bioramani