Re: A Comment on the Lenses (part 2)

[Tom Droege <tdroege2@earthlink.net>]

The filters are "Bessell I" from Omega Optical.  I assume they are "stock" 
since there were no special instructions on the order.  This is something 
that Michael Richmond selected after talking with the expert at Omega Optical.

Tom Droege

At 08:33 AM 11/5/02 -0700, you wrote:
>Dave makes a good point.  I don't remember where you got the I-band
>filters from and whether they were "custom" or "stock".  The Bessell
>Ic prescription, for example, is just RG9 glass, with the red edge
>of the passband formed by the CCD response.  In other words, it has
>a significant red tail in comparison with the Cousins I passband.
>Arne
>
>dave garnett 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
>>>
>>>
>>
>>
>