I accidentally posted this in the "learning" section, but can't figure out how to delete it. I have moved the thread to a more proper location, however: I recently took the first image I've ever taken using 10 minute subframes on my STT-8300m. I usually use 5 minute subframes, but decided to try something a little different this time. I noticed when processing the image that I had a noticeable glow in the upper left corner of the image. It is not really detectable in a single frame, but when the frames are stacked and stretched, it becomes more apparent. From what I can deduce, it appears to be amp glow. I'm curious if anyone can 1) confirm this is the case and 2) tell me if there is any way to reduce the amp glow so that it is less apparent in 10 minute sub frames images. I have attached two images: 1) a stack of 5 minute subframes of the crescent nebula, showing no illumination in the upper left corner and 2) a stack of 10 minute subframes of M81 showing an illumination in the corner (the image was heavily stretched to accentuate what I'm talking about). Both images were taken with the same optical setup. Any insight is most appreciated. Thanks!
For some reason, my images aren't uploading. I can post a dropbox link if that is more helpful if someone needs to see the image.
Best bet is to upload to ftp.cyanogen.com, anonymous login. I recommend using FileZilla (free download). Please let us know the filename once you have uploaded. Quick question though - are you subtracting dark frames?
Doug - Yes, I am subtracting dark frames. The images posted are dark subtracted, as well as calibrated with flats and bias frames. I would have suspected that, if it was amp glow, dark frames would calibrate that out. However, I have confirmed it isn't in the optical system. The same symptoms occurred this past week with the camera connected to my Takahashi FSQ-85...so, I've now seen it in that scope and my TEC 180. But, only at 10 minute subs. 5 minute sub frames don't seem to show it. I've uploaded 4 files to the ftp site: Dahl_TEC5.jpg.zip - a stack of 5 minute subframes of the crescent nebula, showing no artifact Dahl_TEC10.jpg.zip - a stack of 10 minute subframes of M82, showing the bright corner in the upper left Dahl_FSQ.jpg.zip - a stack of 10 minute subframes of the Rosette Nebula, showing the bright corner in BOTH the upper left and lower right. This is on the SAME place on the CCD, but is due to rotation due to a pier flip in the middle of the exposure sequence (I don't rotate my camera while imaging...I simply rotate in image processing). MasterDarkx1(10m).fit.zip - my master dark of 13, 10-minute dark frames. Any help you can give me here would be greatly appreciated. I really want to be able to do long sub frames (15 or even 30 minutes), but I need this problem resolved, first. I would expect dark frames to calibrate this out, but for some reason they are not. I've included my master dark here so you can look at that (in FITS format to prevent data loss). If you'd like the FITS versions of the light frames, let me know. One other note: the moon was up during both the TEC 10 and FSQ shots, which could be a contributor...I have to wait and check again in a couple weeks. However, the FSQ shot was done in Ha, so I would expect it to be less pronounced if it was the moon. Thanks for your time!
One other question: I just discovered the options in CCDOps to turn "Vdd normally off." This is suggested to keep the readout amplifier off except when reading out. That should, theoretically, solve my problem. However, I don't use CCDOps for image capture (I use Sequence Generator Pro). The manual states that these settings are stored in NVM, so does that mean that, if set in CCDOps, they carry over into other programs? In other words, if I set Vdd normally off in CCDOps, will it still be set that way in Sequence Generator Pro? Thanks!
The Vdd is automatically maintain by the driver, so neither application deals with it. If an exposure time is longer than 3 seconds, then the driver switch vdd off during an integration time and resume it after that. So, once again, the driver does it for you itself. Jan
Jan - Ok, thanks for that insight. That must not be the problem then. Any other ideas about what might be causing the glow on the chip in the corner?
Dahl, I think I can help determine if it is amp glow due to a circuitry failure if you could send a single 10 second (actually anything 4 seconds or longer) dark frame, no stacks, no stretch. Just a single dark frame, it doesn't have to be cold even. Post it here or send it to me at bill@sbig.com. There was a recent amp glow in issue in a STF-8300 which was a component failure in that Vdd circuit. I don't know if the driver control Jan mentions above also applies to the STF or not but if the glow looks like the other one then perhaps it could be a circuitry issue. -Bill
