I'm still getting the strange donut on my images of the STT-8300 with the SG filter wheel and AO8. The scope is an Astrotech 10"RC. The scope is collimated. The first image is a luminance flat and the 2nd is a 5 minute sub. As you can see subtracting the flat would make things worse. The dessicant has been baked and cooling set to -30 for about an hour before the image was taken. There are no lights in the observatory and outside was very dark. I'm really frustrated since I've bought the camera new in late April and still have not taken a single image . Please let me know if anyone has advice to correct this issue. Sincerely, Robert Lozano San Antonio
Have you tried taking an image without the cooler running? Try to eliminate the possibility of frost by simply taking the image w/o cooling active. Also check the CCD chamber cover for dew. What's the RH like when you're imaging? Much anything of 90% will likely result in dewing and this can be inside the camera and especially the chamber window itself which may/maynot have heaters installed. You don't need long exposures to see if they are there or not. Just pick a star field and take a 30 second exposure.
I did turn the cooler off and I did notice that the donut went away for the most part. I guess the only question I would have after that is because I've already baked the desiccant what could be causing the issue? The relative humidity last night was about 54%. The plug for the desiccant is on tight and this camera is brand new. It's never had an official first light image. I dread having to take the camera off the scope because it's threaded and to be honest I don't have a lot of time at night to be going up to the observatory but I guess I'll have to. Thanks for the advice! Robert
I'm wondering if you have an internal reflection somewhere. Was the image with the big donut taken with a filter or no ? What happens if you take some frames with the camera on the workbench, not on the back of the scope?
It was taken with filters. It didn't matter which filter I used luminance, red, green, blue or hydrogen Alpha. The results were all the same. For the life of me I don't know what would be reflecting but I do see the benefit and taking the camera off. Given that we don't get to do this Hobby that often it's very frustrating. I haven't tried taking an image with the scope and the camera separated. I guess that's my next step.
So did you make sure the rubber "O" ring was taken off before baking and back on before installing it back in the camera?
Ok, I'd also suggest you take an image with NO filter. (Not clear glass, an open hole). If it recurrs, post the FITs files so us fellow customers can have a look.
Yes, the O ring was removed and reset after baking. I tested the camera last night with the same results. Tonight the camera is coming off for inspection. Thanks
Try doing a flat field without the telescope. The best way is to put a tube of some kind, say 6" to 12" tall, on top of the camera. Put pieces of clean photocopy paper on top - you can add layers to reduce the light level until you can successfully take a picture. If the pattern is still present then it's the camera. If not then it's something with the optics.
I have a very frustrating issue with my new STT-8300. Donuts on the screen that I THINK are coming from the CCD cooling. I have eliminated the AO8-T and filter wheel and still received the donuts. So, I thought the issue is with the camera. To make sure the issue was really with the camera and not the scope I took images with my ST-8300M tonight and received some data that surprised me. The 'CAM ONLY' images are from the STT-8300 that I believe is not cooling correctly and creating a donut image. The other images are from the old ST-8300M with no filters. I will admit the images show a similar aberrant shadow as the STT images. In the opinion's of those on this forum, is this the camera or the scope? The scope is an Astro-Tech 10"RC truss. I have taken numerous images with this scope and it has performed well. Any advice is appreciated! Thanks Robert Lozano
Robert, Have you tried taking any flats and applied them to the images? What is the result? Is cooling on/off? Does it make a difference? NOt sure if this is the same conversation that's been going on a while but just to be sure.
Please provide FITS frames. Please also provide images of the same field with the cooler on and the cooler off. You appear to have an extremely bright star in the frame... that can result in reflections. What happens if you shoot a field without bright stars?
Doug, I get the same bright donut when I shoot a galaxy. I tried posting the link to my previous post but it didn't work. If you look a few days ago I posted ' st 8300 donut.' It has some images there as well. Could you take a look at those? I haven't seen any frosting on the CCD but still have the donut.
This is the same issue that I was having before. My previous posts show the images and this was just an updated version.
Okay, I've merged the two threads. I think one of your ST-8300 images shows signs of frost at lower left. Please try the following: Reproduce the problem with the STT-8300. Then turn off the cooler, let the camera settle to ambient temperature, and then take another identical image. Post both images (in FITS format please).
