[glend (Glen)]

Finished my cold finger 450D today, and I have attached some photos. I didn't have time to do a real good job with the attachment and insulation of the TEC, so excuse the duct tape holding the insulation together. I rushed to get it insulated so I could run a test tonight. If you have a close look at the finger attachment to the sensor frame you will see I chose to make the nylon screws into rivets by melting the rear of the screws with a soldering iron - there is not much room below the sensor frame and I believe by turning them into rivets I have made it as strong as I can. You can also see the additional copper strips that I added to bridge the cutouts and hopefully transfer better; and the Plastidip rubber paint that I used to isolate the finger.

So here is the Test Results:

First I ran the system to cool down the camera to see how far below ambient I could get it. Remember when I built a cooler box with this same TEC it got down to Delta T of 16.9C. With the cold finger running (and the camera turn off) the internal temperature dropped much quicker than the cooler box and within 20 minutes it was down to 8.9C. Ambient was 26C, so the drop (delta) was 17.1C - pretty good for a taped up job.

Turned the camera on (running on the camera battery which does heat up a little over time). Started a run with my interval metre for ten Dark subs at ISO800 of 5 min 20secs (320 secs each) with a 20 sec delay between subs (to see if cool down period was effetive).

With the camera sitting at 9.0C the run worked out like this:

Sub 1: Finish Temp 9.3C
Sub 2: Finish temp 9.6C
Sub 3: Finish temp 9.9C
Sub 4: Finish temp 10.1C
Sub 5: Finish temp 10.3C
Sub 6: Finish temp 10.2C
Sub 7: Finish temp 10.2C
Sub 8: Finish temp 10.2C
Sub 9: Finish temp 10.2C
Sub 10: Finish temp 10.2C

So in 3200 seconds (53.3 minutes) of darks the temperature rose only 1.2C and I suspect some of that is can be attributed to battery heat within the camera, and the Liveview screen being on. After five subs the temperature stabilised and stayed the same for the rest of the run, this is the active base I believe.

There was no evidence of the external body of the camera cooling significantly and no condensation on the camera body, in the lense, or on the area where the finger enters the camera. Internally, it was purged with argon before I started so no condensation.

When I stopped the test, leaving the camera powered up, the temperature dropped back to 9.3C within 7 minutes and stayed there - so I think that's the 'on power' baseline with no activity (and a warm battery).

Once I turned the camera off the temp dropped back to 9C within 4 minutes, at which point I turned the system off.

So I am pretty pleased with the results, I still have to have a good look at each of the darks but I think they will be ok. One thing I need to address is the fan mount, as it is transferring vibration to the camera, which will be a problem during imaging. There is no isolation of the fan - its screwed right into the vanes of the heat sink - so I will be looking for a better heatsink fan solution (anyone recommend one?).

Photos are attached, the last two show the beginning of the test and the temp after three subs.

*** Update: Once the camera had sat overnight I removed the back of the camera to verify the effectiveness of the argon purge and there was no moisture present anywhere internally.