patbob wrote:
> What do people think of the possibility of designing our own CCD
> back for a Pentax camera (assuming, of course, that Pentax isn't coming
> out with one anytime soon)?
Hi Patrick,
There was a brief discussion about this very idea on the list a few months
ago. This certainly could be done. The big issue, of course, would be the
cost of a 36mm x 24mm full-frame CCD sensor. The TI 255 chip that some in
the amateur astronomy community use is fingernail-size. But a 36mm x 24mm
array? How DEEEEP are your pockets? Would be interesting -- just for fun
-- to see if Kodak, for instance, has such a CCD available to folks like us,
and what it would run if purchased in single quantities. Any professional
astronomers on the list?
Another interesting thought is the use of a CMOS sensor instead of a CCD.
The cost goes down since with CMOS sensors, you can use standard fabrication
techniques to put the associated electronics on the same hunk of silicon as
the sensor array. The trade-off, if I understand the underlying physics
correctly, is that the dynamic range and sensitivity go way down as well.
Nonetheless, this would be a cheap route to consumer digital imaging. I was
shocked (well, not really) to see in an ad in a recent Outdoor Photography
issue that the new USD $3000 Canon D30 digital SLR body has a CMOS sensor
instead of a CCD! Aarrrgh!! Blasphemy!! Hell, that's a $3000 baby
monitor, not a camera! And it's STILL not full-frame! :-) If your budget
allows for bodies costing in excess of USD $5000, there's the soon to be
available Nikon D1. It's got a real CCD, but even this one is not
full-frame (only 24mm x 16mm, IIRC). Worse yet, the maximum effective speed
of the sensor is reportedly only ASA 800. My personal opinion is that
there's still an unacceptable trade-off between resolution and sensitivity
-- as you cram more pixels into the same format, each pixel necessarily
becomes smaller and consequently less sensitive, since it is now capturing
fewer photons than a pixel of larger area. Nikon has settled on a 5.5 MP
sensor in order to keep maximum effective ASA of the sensor at a reasonable
level. If there's a giant leap forward in sensor array design (avalanche
photodiode array??), we might get to the point where we can have high
resolution AND high sensitivity, but I think that's a ways off in the
distant future.
But I still like that idea about a home-made CCD back on a K-mount body.
Keep thinking about it, and let us know when you start making a prototype!
Bill Peifer
Rochester, NY
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