Re: A Comment on the Lenses (part 3)

[Tom Droege <tdroege2@earthlink.net>]

Ahhhh!  The problem is that no one understands the problem.  As I have 
described, the lens design has a checkered history.  Some of you out there 
have the lens design files and know what to do with them.  I do not have 
them or any idea what to do with them if I did.

I think that everyone out there understands that we would not design a 
program with built in problems like this.  Still, we have come a long way, 
and can now produce pretty good data.  My reading of papers indicates that 
we are doing as well as others attempting this work.  We can still make 
some improvements.  I am anxious to start a real survey.  I hope to start 
this in the spring,  after I have completed the current round of 
modifications.  While the weather is bad, I plan to make changes using the 
occasional patch of clear sky to make tests.  By spring I should have 3 
debugged systems and can start doing the whole northern sky down to -12 or so.

All things considered, the lens design is a lot better than the camera 
lenses I have tried.  It is probably better than the (expensive) camera 
lenses that others are using for this kind of work.  At least ASAS quotes 
much larger attenuation in the corners than I see.  Our design should make 
correction easier.  So we are in a not so bad position, I think.  It may be 
that something trivial can make a big improvement.  I am hoping that one of 
you that has the lens design can share it with us.  There may be new 
lurkers that have not been through the previous effort and who could now 
step in and look at the design and suggest improvements.

If someone steps in and makes suggestions I will try them if I can.

Tom Droege

At 04:13 PM 11/5/02 +0000, you wrote:
>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
> > > >
> > > >
> > > >
> >
> >
> >