Three Fathoms Observatory
Stewart Yeung








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Suspected CCD Frost (?) Problem


Image taken at -3.1° 10 minutes after turning on CCD cooling

Ambient Humidity at 50%

The rough-looking area (=Frost?) first starts at the perimeters and expanding inward towards the centre.

Then the rough area reverts its expansion and shrinks outward gradually until it disappears in about 30 to 45 minutes.


Advice was sought form experienced astrophotographers in the SBIG discussion forum. The problem was easily identified and confirmed as frost by veterans.

As advised the desiccant plug with the "O" ring removed was baked for 2 hours (4 hours is the norm, I took a short cut ! ) in a home baker of radiator type.

Temperature was kept by guesstimate to under 200°C. The supplied dummy plug with its "O" ring was used to fill the emptied hole of the CCD during the baking.


Frost still persisted for 40 minutes the first time of imaging after the regenerated desiccant plug was put back. I was disappointed and consulted the veterans again.

I was advised that it took time (1 to 2 hours) for the regenerated desiccant to absorb the existing moisture in the CCD chamber (also stated in the CCD Manual).


The next time I started to image with the cooled CCD, the very first image was already free of frost !

So the desiccant regeneration operation has been a success, thanks to :



Wolfgang Renz, Joe Mize, Michael Sherick, Peter Vasey, Michael Stauning, Eric Africa, al.tuttle, Ron Brant, et al.