Test results:

With Clouds increasing, and running short on time, I was able to conduct a preliminary test of the CPU fan modification. After opening up my observatory, I immediately took the camera out of it's storage desk drawer and plugged in the fan to a 12-volt power source. After a few minutes, the camera was noticeably cooler to the touch. Once the camera had been powered on for about 10 minutes, I engaged the deep-sky mode (sense-up to x128, manual gain 18db), and waited a few minutes for the video image to reach maximum integration range. I then examined the video image with the lens cap on the camera. There was a definite improvement in the number of "warm pixels" that were visible. Only the five or six permanent 'hot' pixels were showing up. There were very few of the 'warm' pixels associated with the buildup of internal heat on the CCD chip.

Before            After

So far, the fan mod was working to expectations.

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I then attached the camera to my 8" SCT Celestron Ultima, and located the globular cluster M22. While tweaking the finderscope alignment, I noticed that the star images were a little soft. Here's a quick unprocessed single image of M22 with the fan off & on.

Fan off      Fan on
I switched the fan off, and took the camera out of deep-sky mode. I centered on a close by moderately bright star (in the handle of the 'Teapot'), increased the camera zoom to 2x, and got a fine focus. Then I turned the camera fan back on (12-volt power source). As you can see from the image, there now is a problem. This is caused by having a small vibration from the high-speed fan.

Fan off      Fan on
By adjusting the fan's velcro mounting, I am able to affect the star image distortion, so if I can add some additional material (thicker velcro or doublesided foam weather-stripping?) between the camera and the fan, I may be able to isolate/eliminate the vibration. I also tried underpowering the fan by using a 9-volt power source, and was able to nullify the vibration.

Fan on 9-volt power

So the solution to the vibration problem will be either adding insulation between the camera & fan, or underpowering the fan, or even switching to a lower-volumne CPU fan.

This wraps up the preliminary test of the Stellacam Ex CPU Fan Modification. Stay tunned for the next test installment......