This night I dreamt about zero cloud forecast for the next 3 nights. Unfortunately it has nothing in common with reality – the weather is as it is and there is no single symptom telling it will improve soon. So I continue preparations for the astrophoto season 🙂
Insprired by this link I decided to add passive cooling to my QHY5 guider camera. The implementation is very straightforward assuming your QHY5 camera has already cut out piece of the board under the CCD chip. Then all you need to do is to place there a piece of aluminum (or copper) that will fill the space between the chip and the camera case. The PCB cut out is 9x10mm large, so you need to choose the proper cold finger size. In my camera the distance between chip and camera case is 15.3mm, so I choose aluminum rod 8mm diameter and 15.3mm length. I drilled a whole at one end for 3mm bolt and fixed the cold finger to camera case. Both cold finger surfaces are covered with thermal grease.
One important thing is that cold finger surfaces need to be flat, so it will contact with case and CCD chip with the whole surface area. And that is all – camera was assembled and I performed a few tests. Three series of dark frames were taken with and without cold finger. Exposure times were 3, 5 and 30 seconds, and each serie lasted for 5 minutes. There was 15 minutes break between each serie to cool down the camera. Ambient temperature was 21C. Here are sample picture crops from the images taken at the end of each serie (click to enlarge):
|Exp. time||Std dev. HOT||Std dev. COLD||Hot px val HOT||Hot px val COLD|
Cold finger solution seems to work fine and I have high hopes it will improve stability of guiding process, especially facing the fact that hot pixels are the major pain of QHY5 camera. It probably also benefit when using this camera for making planetary exposures.