I was hoping that the problem I am having with my ST8300M was condensation and that the desiccant package Bill Lynch sent would fix it. But it didn't. Here is a link to a recent image taken with the camera. https://1drv.ms/u/s!AtEaGCq_HdNIg4AzmrV-0dRrMxdjyw It is a single 10 minute exposure taken through an Ha filter with the cooler set to -5 degrees and the camera achieving -3 degrees. It has been auto-stretched with Pixinsight. The bright areas on the left of the image are the problem. The pattern varies substantially from one frame to the next but the image is typical of all frames. Do you know the cause? What is your recommended remedy? Scott Dixon
I'm pretty sure there are no light leaks but here is a .fits frame https://1drv.ms/u/s!AtEaGCq_HdNIg4A0beflzOLVLphDrg
Here is a single dark 600 sec. It is several months old and the problem may be worse today. Temperature is in the .fits header. https://1drv.ms/u/s!AtEaGCq_HdNIg4A1ciNgCB1USyL4-g
I did send a link to an unprocessed (RAW) dark before I sent the processed image link. Here it is again. https://1drv.ms/u/s!AtEaGCq_HdNIg4A1ciNgCB1USyL4-g
Odd that the anomalous signal is so much stronger in the light frame than the dark frame. Let's try and rule out some sort of software incompatibility. Make sure the camera firmware is up-to-date (using SBIG Driver Checker). Then try taking a 600 second dark image with the latest version of CCDOPS software.
Here is a link to a fresh dark. 45 minutes after sunset. No local light sources. Telescope lid on. Temp at -1.1 C. Set to -5 C. https://1drv.ms/u/s!AtEaGCq_HdNIg4A3yHbARr97NFeBsg
Why are you running with a setpoint below what the camera is actually achieving? That will result in very poor temperature regulation. You want to make the setpoint a few degrees ABOVE the minimum temperature, so it can regulate. I can see a slight ripple on the left side of the dark frame. This is not unusual and generally not a problem as long as dark frame subtraction is performed correctly. Which is very hard to do properly if your temperature regulation is not working because the setpoint is too low. The slight ripple would be caused by something in the electronics. There are several possible sources including the analog chain and the power supplies. In our modern cameras we've made quite a bit of effort to eliminate it, just because I'm very fussy, but some older models do exhibit a slight ripple. If you want to get rid of the ripple, you could get your camera upgraded to STF, but there would be a cost. Contact Bill @ service for details. But I really don't think you need to do that. Careful calibration should remove the ripple. Caveat: the ripple looks much bigger in your light frame. Did you do any processing on the image? It would be helpful to have another raw, unprocessed light frame to compare.
Doug You caught me being sloppy. The temperature setting was -5C and that was too cold but I didn't bother to set it to an achievable temperature. Normally I would be more careful. Last night I took a few more images to further debug this problem. I've uploaded 5 images (lights, 600 sec., Ha filter) taken Sept 10th and 12th. Image 4749 was taken on Sept 10th when the condition was quite evident and is like the image I previously provided. The other four were taken last night. I wanted to eliminate stray light as a cause. All 5 images were taken well after dark in a building with black walls. During imaging there are three light sources in the building; a red LED, a Blue LED and a laptop monitor. Image 4749 from Sept 10th was taken with no protection from the three light sources although the laptop screen was folded down and not fully illuminating the area. It clearly shows the problem. Image 4768 was taken last night with all three light sources covered. It does not show the problem. But the next two images 4775 and 4783 were taken with the light sources unprotected and the laptop screen extended and fully illuminating the area. 4775 does not show the problem and 4783 does show it a little bit. The last image, 4789, has the light sources covered and also shows the problem a little bit. None of the 4 images taken last night are as bad as the one taken Sept 10th and the other images taken Sept 10th that I have not shared. The problem seems to vary considerably from night to night and also within an image sequence taken on a single night. I know of no differences in the setup or conditions between the Sept 10th images and those taken last night. From last nights images I don't believe there is a light leak. Scott Dixon
So the problem is intermittent. Nasty. Is there any correlation of the symptoms with the ambient air temperature? (Not the CCD temperature, but the air temperature, which affects the temperature of the electronics in the camera.) My best guess is that one of the internal power supplies is going metastable. The vertical CCD clocks have a lot of capacitance and driving them can cause ripple on the power supply, which can work its way into the signal processing through various routes. One possibility would be a failing filter capacitor in one of the internal supplies. But with a subtle symptom that comes and goes it would be really difficult to track down. To fix this as it stands, Bill would have to change the circuit card. ST cards are obsolete, so it would be an STF card. The main difference is that it reads out faster. Unfortunately this is not an inexpensive repair. Bill would have to quote it, but it'll be ballpark about 1/3 the price of the camera. One option is to simply live with the problem for now, crop your images slightly, and wait to see if it fails hard. A hard failure on the board might be repairable because it would be much easier to find the bad component... but depending on the situation it might still require a board replacement.
Doug thank you very much. The temperature on the two days those 5 images were taken didn't vary by more than a few degrees. I'll look for correlation with ambient temperature. Until I get a hard failure I'll just live with it. Scott
Scott - is the camera being powered by the original AC power supply or something else? Is it sharing a power source? Is everything going to a common ground? Just wondering if there is another load (dome motor, mount motors, PC) that is causing electrical issues.
The camera and mount are powered off a single AC to 12 volt DC power supply and they have been for years. I'll try powering the camera with a different supply.
