Re: A Comment on the Lenses (part 2)

[Tom Droege <tdroege2@earthlink.net>]

Dave,

Possibly you meant a 50 mm radius stop?

If you have the lens files then possibly you can suggest where to put the stop?

Tom

At 11:01 AM 11/5/02 +0000, you wrote:
>I've just looked at the lens design files again. They are designed for a
>50mm dia stop just in front of the front lens, but it is noticeable that
>some of the internal rays pass very close to the edges of lenses, so it is
>possible that the real stop may be internal.
>
>I note that the design spot size is small for wavelengths in the range 0.715
>to 0.880 - outside of these values the spot size increases rapidly. So, for
>good quality images you need to be sure that the filter is doing its job.
>Presumably the ccd chip is very sensitive at this end of the spectrum, which
>will exaggerate any filter leakage ...
>
>Dave
>
>----- Original Message -----
>From: "Tom Droege" <tdroege2@earthlink.net>
>To: <tass@listserv.wwa.com>
>Sent: Tuesday, November 05, 2002 5:19 AM
>Subject: jA Comment on the Lenses
>
>
> > As noted earlier, the wide open I lens is down 5% at the edge (on a circle
> > tangent to the sides of the CCD) and 10% in the corner.
> >
> > I note that now I have stopped down the I lens, it is down more like 20%
>in
> > the corner.  This surprised my feeble knowledge of optics.  I thought
> > everything got better as you stopped down lenses.
> >
> > Possibly an optics expert can respond?  In any case, we are still
> > considerably superior to camera lenses which are often 50% down in the
> > corners of images of our size.
> >
> > Tom Droege
> >
> >
> >