At 3:35 AM +0200 6/6/04, Listar wrote:
>Date: Fri, 04 Jun 2004 21:14:35 -0700
>Subject: [OM] Re: E-1 discussion
>From: Jim Brokaw <jbrokaw@xxxxxxxx>
>
>on 6/4/04 7:12 PM, Joe Gwinn at joegwinn@xxxxxxxxxxx wrote:
>
>> I wasn't clear about this, but when I say "astronomers", I mean the
>> pros, the ones with the telescopes costing hundreds of millions of
>> dollars. In that world, for the image sensor, cost is simply not an
>> issue, so they push the technology to its limit, allowing us folk
>> with lesser budgets to see where those limits are.
>
>Aren't these pro astro image sensor usually refrigerated (or chilled liquid
>nitrogen or such) to reduce electronic noise to a minimum...?
Yes, to control dark current, allowing long exposures before the
integrated dark current becomes too big a problem. Other kinds of
noise are basically unaffected, but are not really random and so
subtract out.
Liquid nitrogen is typical in astronomy. Liquid nitrogen is
cheaper than milk, and available in industrial quantities.
Not as good, but with easier logistics, are thermoelectric coolers.
>Maybe that's the next new thing in digicams... comes with a little
>tank of liquid
>nitrogen.
A chilling thought. I can just see it, the nice little camera, all
black, but frosted, with a contrail.
One can buy amateur CCD cameras with thermoelectric cooling for use
on small telescopes today, for US $5000 to $10000. By all reports,
these work well, but take a very hefty battery. Think a lead-acid
automotive or motorcycle battery, largely to run the cooler.
Joe Gwinn
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