From: bob piatek <bobtek@fishcamp.com>
Date: August 13, 2005 3:57:31 PM MDT
To: Astro_IIDC@yahoogroups.com
Subject: Re: [Astro_IIDC] Re: Cooled Flea Camera Shots
On Aug 13, 2005, at 8:13 AM, Tim wrote:
Does adding a cooler to a camera that doesn't already have one introduce thermal stresses
to the internal components (the ccd and the electronics) that might damage them over
time? Could a less agressive cooling system work well enough (like putting heatsinks on
the sides of the case with a fan or two blowing across them)?
In general additional cooling is probably helpful. Heat is a major enemy of electronic components.
The problem is where you try to get too aggressive with the cooling. Semiconductors have a temperature rating spec that shows an operating temperature range over which the chip's specifications are guaranteed. That's not to say that the chip will not function outside that range, just that its specifications are not guaranteed. Things like timing margins usually get worse at high temps for example.
Cooling a chip to temps in the -30C range is probably outside the temperature range of the image sensor used on most cameras. Milton probably could get that on a February night where he lives but the people living in the Arizona desert won't see that. There is a posibility that if you cool to those types of temperatures, you could damage the chip. Things like differences in expansion coefficients between the various parts of the image sensor might cause something to crack. In practice, it has not been a problem with even 3-stage TEC coolers.
The performance of the image sensor with regard to dark current does improve remarkably with cooling. The dark current is cut in half for each ~8C in temperature drop. So with a -25C temperature drop you would have only ~12.5% of the dark noise in your pict compared to that of an uncooled chip. That seems to hold true for both CMOS as well as CCD image sensors.
Bob Piatek
fishcamp engineering
105 W. Clark Ave.
Orcutt, CA 93455
TEL: 805-937-6365
FAX: 805-937-6252