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Hi Steve
Just remembering from my old Cookbook camera days which involved making the camera and interface electronics. It had the ccd chip mounted directly on the cold side of the Peltier. The aim was to get the chip down to about -30deg C to get decent noise suppression on the old fashioned Kodak ccd. Temperature was measured by a small temperature indicator transistor imbedded next to the ccd chip on its "cold finger". Dewing up was avoided by slowly increasing the Peltier current. As the cold finger got colder quicker than the ccd, any moisture in the sealed camera first formed on the cold finger and then froze leaving the ccd cold and dry!
I too have modified my DSI2 by slicing the cooling fins off the back heat sink, sanding the aluminium surface completely flat and then mounting a neat little fan/heatsink (to get rid of the Peltier heat)/ Peltier with the cold side on the flat DSI heat sink. A normal 40mm square Peltier neatly fits the fan/heatsink which I rescued from an old Pentium 2 computer where it was used to cool the CPU.
In summer my DSI2 can reach and indicated temperature of up to 35deg C. At this temperature, noise on long exposures is rather heavy. I usually cool the CCD down to an indicated temperature of about 19degrees C where the noise is acceptable. This only requires 5 volts at 0.5 amps into the Peltier which I derive from my astro PC.
I had thought about putting drying material in the camera so that I could take the CCD lower without fogging up but I have not gone to this trouble yet. I guess also from my Cookbook experience that if I did go well below the ambient dew point that any moisture would form on the DSI2's cold finger before forming on the ccd - must experiment with this one day!
Cheers Peter
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