Correction?

Started by ghacker, 11/19/2006 06:53PM
Posted 11/19/2006 06:53PM Opening Post
Have a question for the more knowledgable. Frequently in scope reviews you read a comment that the optics are over or under corrected. Can someone educate me on what this means and the practical implications?

Thanks in advance.

Dennis
Posted 11/19/2006 10:11PM #1
http://aberrator.astronomy.net/

And down load the freeware....
Posted 11/20/2006 05:13PM #2
Correction in this context means adjusting the shape of the mirror so that all the rays of light focus in the same place. If one does not do this, the light from the outer regions of the mirror (further from the center) will focus shorter or longer than the light from the inner regions (towards the center).

With an under corrected mirror, the marginal rays cross nearer to the objective than the central rays. With an over corrected mirror, the marginal rays cross further away from the objective.

In either case, the light is not as tightly focused as it should be. The practical implications:

Object does not come to a crisp focus, but rather slides through focus.

Object is not as bright as it otherwise would be because whatever light it has is spread over a slightly wider area.

Alex