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By Adam J
I have decided to create this thread to take anyone who is interested through the design and construction of my DSLR Cool Box over a series of posts.
I made my start in astro-photography / DSO imaging about 18 months back using a Canon 1000D on a 130DPS / HEQ5pro.
I have a very limited budget and so almost every piece of equipment I own is second hand or self built. Living in a yellow zone area I started out using a Astronomic CLS filter and this worked well for me for a short period. However, once I started guiding it became clear that I was limited by light pollution in longer exposures. To that end I decided that I wanted to try narrow band imaging, but I knew that I could not afford a mono CCD or CMOS camera to go with the narrow band filters and that with my DSLR I would suffer from low signal to noise ratio if I attempted narrow band imaging through the Bayer Matrix.
I initially looked into debayering a DSLR in an attempt to get more signal and I did in fact manage to successfully remove the bayer matrix and create a good quality mono sensor. However, extensive testing convinced me that this was not the way ahead and that I had in fact lost performance overall due to the loss of the micro lenses along with the bayer filters. As a result I decided to focus on the other side of the S/N equation and have a go at reducing the noise through cooling.
All of this of course has been well covered by others in the past, however I would hope that my approach has proven to be a good one with some original design elements and so it sill worth sharing.
I began by researching ‘do it yourself’ DSLR cooling, as I said I am certainly not the first to have attempt this and a wealth of information exists on the internet not least this forum. It was immediately apparent that no two approaches are the same, but it was possible to group DSLR cooling into two main methods both of which make use of Thermal Electric Cooling (TEC) modules, a TEC being a solid state heat pump that uses the Peltier effect to draw heat from one side of the module to the other. The module itself consisting of two ceramic plates sandwiching a semi-conductor matrix. When a voltage is applied across the TEC one side of becomes hot and the other cold.
Cooling Method 1: The first method is very similar to that used in commercially available CCD cameras and uses a copper plate or ‘cold finger’ in direct contact with the rear surface of the DSLR CMOS sensor to remove heat through conduction. This consists of a copper plate cooled by a TEC which is in turn cooled by a heat sink and fan. While this method is extremely effective in cooling the CMOS sensor it requires significant modification to the camera which carries a significant level of technical risk, problems can also occur with condensation inside the camera body due to the low temperature of the cold finger.
Cooling Method 2: The second method leaves the camera body intact and places it within a ‘cool box’ enclosure (essentially a miniature fridge). This effectively lowers the ambient temperature of the air around the camera which in turn leads to the temperature of the CMOS sensor being lowered. The effects of this type of cooling on noise can be simulated by placing a camera into a fridge on a hot day and taking a long exposure dark frame before and after cooling. While this method is lower risk than the direct cooling method it does come at the expense of bulkier less efficient and less effective cooling. However, I selected this method for my cooling project as the primary goal is to improve performance with minimum expenditure, accidentally destroying a perfectly good DSLR camera would not aid me in this goal. The ability to seal a DSLR within an air tight box would be essential in preventing dew from forming.
To be continued:-