 | Thank you for the info / correction.
"BC" wrote in message
> A single element lens can be completely corrected for third order
coma
> and all orders of spherical aberration with a single aspheric
surface.
The other being...spherical, planar?
In general spherical, although if you are free to vary the refractive
index you could make the rear surface plano.
By corrected for all orders of SA do you actually mean stigmatic on
axis for
a source at infinity?
Yes, stigmatic on axis for a source at infinity.
> In a fast lens there will be higher order coma, which can be
> effectively corrected with a bi-aspheric design. This is the basis of
> the objective lenses used in all CD/DVD players.
Concerning the CD/DVD lenses how do they take care of the large SA
caused by
the plastic layer, especially at high NA? By introducing a certain
amount of
SA of the opposite sign?
The cover layer just becomes a part of the design, and poses little
difficulty. The only time it really becomes an issue is if you want to
reduce the lens size as much as possible, and you have to start
worrying about the BFL.
Brian
www.caldwellphotographic.com
|
|
