T3D Re: Lens testing

[john bercovitz <bercov@xxxxxxxxxxx>]

> how far do the lenses need to be from the film plane?  But I 
> would really like to know how I can calculate this for any lens.

Calculating this is not trivial because you need to acquire a
lot of data - lens element materials and spacings - and then
input them in a ray tracing program or do by hand a lot of 
calculation I personally don't enjoy doing by hand.  If you
have a PC, there is a freebie version of OSLO called OSLO LT 
on the web at:
http://www.sinopt.com/

You can do a first order calculation without too much work
but it may or may not be really useful since it will only
tell you about rays lying very near the optical axis.  And
again, you would still need all that input data.

The better thing to do is to just test the lens as Greg suggested.
If you have access to an optical bench, there are a lot of great
things you can do.  

Even without an optical bench you can take a picture of a grid
hung on a wall to see if there is any distortion.

John B


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