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Hi Nicko. Following your exploits...well done.
To quantify how well your image noise has improved you need to take darks at various temperatures and to a std deviation pixel count on those darks. I used imageJ (freeware), converted the darks to TIFFs using DPP then measured in Image J.
There are other methods to do this.
What you want to do is compare std deviation of noise across differing sub lengths and ISO's to get an idea what's best (lowest noise) Vs sensor sensitivity for you.
The other issue I found with DSLR coolers is that they cool well when run with the camera but the nose piece conducts and lowers thermal efficiency quite a bit. You will need to insulate/cover this area of the focuser DT. This also decreases thermal efficiency somewhat and I found it can be an hour to cool the DSLR to acceptable temps. About 1/2 hr if not connected to the scope! Probably why some people use qty 2 peltiers coolers on DSLR cool boxes!
That said any CMOS temp (use Exif data) below around 10~8 C will see vast improvements in lowering noise on Canon DSLRs.
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