Re: A Comment on the Lenses (part 3)

["dave garnett" <dave.garnett@metapurple.co.uk>]

Yes, the front stop should be 100mm diameter !

I'd be reluctant to pile in with lens modifications without understanding
the problem. I haven't been following the thread in detail, so perhaps
somebody could summarise ?

Dave

----- Original Message -----
From: "Tom Droege" <tdroege2@earthlink.net>
To: "dave garnett" <dave.garnett@metapurple.co.uk>; <tass@listserv.wwa.com>
Sent: Tuesday, November 05, 2002 3:33 PM
Subject: Re: A Comment on the Lenses (part 2)


> 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
> > >
> > >
> > >
>
>
>