Well, almost. Theres only so much the might of ingenuity can do for over-the-counter technology. I wanted to share my discoveries with you so that you might be able to dissemenate the information to anyone else interested. Since the search engines seem to see you as a central hub in the concept of QuickCam astronomy. :)

I had seen information from several articles and persons stating that cooling the QC grayscale does no good since the camera circuit board is just not set up to work for long exposures. I fixed that problem. I can now take exposures several minutes long. The greatest key to success was to disable pin number 8 (the antiblooming gate). The AB function, while trying to limit overwell capacity on the pixels, also tends to rob them of more than it should. It is also set by the manufacturer at too high a voltage so it introduces some noise of it's own.

I found that placing a trimpot between the ABG on the chip and it's contact point on the circuit board allows for optimizing the AB function to any light condition or dropping it out completley for fairly long exposures. The best image of a pitch dark scene that uncooled exposure with ABG on is almost nothing but pure shot noise and static if anything at all. But with cooling and ABG off the same images are now crisp with good contrast and almost zero static or shot noise. The cooling also removes all of the "hot" pixels you usually see in certain permanent locations on the image. The difference is so staggering it might as well be the difference between a Meade Pictor and a $20 Tyco KidCam

Also, I temporarily replaced the 25 MHz clock on the circuit board with a 4.5 MHz crystal as a test. This increased exposures controlled by the slider bar to over four times as long but the software shutter speed control still times it to whatever seconds you specify. I had altered the timing in the hopes that it might help decrease EMF interference but I saw no benefits gained so switched back to the 25 MHz speed.

Also, I am using a 33 watt cooling chip from Melcor and I run the CCD at -20 F. I have seen no ill effects whatsoever from running it far colder than the 14 F that Texas Instruments lists as it's lower operaing limit.

For anyone who tries these modification I would point out that all the usual setting to get an image change drastically in the cooled/ABG off mode. It is easy to think you have fried the camera the first time you try it after modification. Also, any wires used to extend the chip from the circuit board to allow for a cold plate must be kept under three inches in length and sheilded in some way. Especially wires 5 through 8. If there is nothing but white on the image then pinch wires 5 through 8 together. If dark lines or patches creep into the screen then the wires need to be wrapped with a length of grounded wires to "weigh" them down and keep them from jerking to each others EMF.

Also, placing a trimpot on the ABG function help to greatly improve exposures over 1 second long even if you do not cool the camera.

And on a final note. Some of the grayscale QC's come with a Texas Instruments TC255 chip while others have a Japanese chip which I have been unable to identify or get information on from any supplier. I have tested the frequencies and voltages on each of the pins and functions on both types of chips and they are perfectly identical to each other in performance and requirements except for the physical shape. The TC255 is square in shape whereas the Japanese chip is the standard rectangular form. The modifications I have carried out on the TC255 worked exactly the same on the Japanese chip.


Matt Herriot