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By Tom OD
Happy Christmas SGL,
I m finally getting around to processing images from this year, and this is the last TEC image.
Olly already posted his version about 5 months ago
This is 7 hours of LRGB, in Sagittarius. There is virtually no background sky in this region, being so close to the centre of the Milky Way. What you do get though is a super field of Red / Orange / Golden stars, in what I believe is a dusty region of the sky.
Comparing this TEC data to the two panels of the FSQ data that have M22 in it from my Galactic Centre mosaic, I see that I have the same darker regions in all three images. Perhaps there is a Ha signal lurking in there.
Attaching a cropped version at 100% also.
I've decided to have a play around with some DIY cooling and bought a 5V peltier cooler to do this.
Now I went for 5V as I wanted to be able to power it from a USB port, I have some battery packs that are designed for charging up phones and tablets that will come in handy for portability.
The ZWO cameras are quite well designed for this type of thing as they have a large flat backplate that the cooler can be attached to.
I used a thermal interface pad to attach the TEC to the back of the camera and another one to attach a CPU heat sink with fan from an old computer.
The fan and cooler are then connected up in parallel to two battery packs or to a single 5V mains adaptor.
Now for the testing, I ran the camera in video mode for a while and the temperature settled at 36.7°C with no cooling on. I kept the gain at 255 throughout the tests.
When I turned the cooling on the temperature quickly dropped down to 16°C.
Next I did some longer exposures, after a 5min exposure with no cooling it reported that the temperature was 32.2°C and on inspection the average pixel value was 1187.
Now with the cooling on I took another 5min exposure and it reported the temp as being 10.2°C and the average pixel value was 216.
I took some 1min exposures as well, these came up with a pixel value of 198 for uncooled and 17 for cooled.
I noticed that a lot of this noise was in the corners, I assume that this is amp glow or other interference from the internal electronics so I cropped it and the average pixel value dropped to 180 for uncooled and 8 for cooled.
Cropping the 5min exposures brought the average pixel value down to 1038 for uncooled and 80 for cooled.
This seems to be a resounding success so far as noise reduction goes, I expect that the amp glow can be dealt with using dark frames as it isn't random noise.
I also noticed that the majority of the noise is in the same pixels in the cooled exposures, as such it should respond well to dark frames or a bad pixel map.
I plan to use this with some camera lenses I have as a super portable setup, maybe it will be portable enough to take somewhere with no cloud
As I haven't had any sessions for a while I needed something to do with my astronomy before I forgot what it was all about. So, (don't you hate it when people start a sentence with "So"!) having read an article in Astronomy Now about building a Peltier controlled coolbox for a DSLR camera I thought I would give it a go. My main reason for doing this is that I am not too keen on taking my DSLR apart to do the more radical Peltier cooling that some members have done. Yes Gina, I'm looking at you!
My coolbox is slightly upgraded from the one in the article as I have put a copper ribbon cold finger from the Peltier exchange heatsink to around the DSLR body (bottom and back).
The Peltier cooler was purchased off of the internet and came all the way from China in a plastic bag with a bit of bubblewrap around it so needless to say it was damaged when I received it, but nothing I couldn't fix and I wasn't going to send it back for only £8.
The insulation was from an old camping mat that I bought some time ago to make a dew shield from but was too floppy! The box was one of those food storage boxes that locks twice and the copper was 'rescued' from the scrap bin at work!
The power to the DSLR is via the battery hack that can be found in this forum.
After completion I ran a test indoors and recorded the results via APT which give a cmos temperature reading from the RAW file. Room temperature was a steady 23.5 deg C throughout the test. I set up APT to take 100 frames with a 60 second gap between each frame. The first few readings were at 24 deg C, by the time the test ended APT was reporting a cmos temperature of 13 deg C. That's an 11 deg C drop in temperature over the course of the test and a 10.5 degree drop over ambient temperature.
All I need now is a clear night to test it out in the real world.
I thought I would share with you last summer's project to add set-point cooling to my DSLR. It took about 3 months and wasn't actually required much over the cold winter months. I've made a few minor changes since the winter. The original white-on-blue display packed up so I replaced it with this black-on-green one. And the original ball-bearing fan introduced vibration when using my SCT (not apparent on my other scopes), so I've replaced it with a MagLev/vapo type. Unfortunately I haven't had any clear skies to test the new fan...
My main design criteria were:
Cold-finger/peltier cooling As little 'destruction/deconstruction' of the camera as possible - I wanted it to still look like a DSLR Achieve 5-10 C set-point cooling, as I felt this gave acceptable low noise Include a dew heater/indicator for the front filter Arduino controlled with display to provide useful feedback on settings and simple controls I give due credit to Gina and Rowland Cheshire, having read their many inspirational posts on cooling (both here and on Ice in space) which helped me to hone my design.
Image with the camera shows fan-heatsink-peltier-bracket construction. The connection box is screwed to the tripod mounting. The white sensor measures ambient temperature and RH. The controller images show approaching the set-point and at set-point. A red LED above the main display lights up when the dew heater is active. The display shows:
Set = desired set-point temperature CMOS = temperature of cold-finger close to sensor Fltr = temperature of front filter Dew = number of degrees above the dew point to maintain the dew heater TEC = heatsink temperature (hot side of peltier) PWM = percentage output sent to the peltier (I've limited it to 90% max) Am = ambient temperature, DP= dew point, RH = relative humidity At some point I will tidy the heatsink side to conceal the cables, etc.