STT-8300 image problem

Discussion in 'STT Series' started by Stuart Gray, Jul 19, 2020.

  1. Stuart Gray

    Stuart Gray Standard User

    Joined:
    May 25, 2015
    Messages:
    7
    Images from my STT-8300 show a darkened region across the top and bottom edges. (see attached fits image). The camera is attached to an FW8G-STT self-guiding filter wheel and is imaging through a 130mm refractor operating at f/5. The pick off mirror for the guide chip in the filter wheel has been adjusted to be out of the frame.

    Stuart
     

    Attached Files:

  2. Colin Haig

    Colin Haig Staff Member

    Joined:
    Oct 27, 2014
    Messages:
    4,280
    Hard to say. Can you send over a bias, dark, flat,and light image, (preferrable produced by CCDops instead of PixInsight)?
    I noticed the camera set point was -30C, yet the chip was at 0C.
    Was it a really hot night?
    Have you baked the Desiccant any time in the last 6 months?
    Anything change in your setup recently?

    I'm going to loop in @Bill in case he has an idea.
     
  3. Bill

    Bill SBIG Service and Repairs Staff Member

    Joined:
    Oct 12, 2014
    Messages:
    485
    Can't say I've seen that before. Looks like a mirror obstruction but... on the top and bottom? Not sure...
     
  4. Colin Haig

    Colin Haig Staff Member

    Joined:
    Oct 27, 2014
    Messages:
    4,280
    Have you had a look down the nose of the camera when the shutter is open?
     
  5. Doug

    Doug Staff Member

    Joined:
    Sep 25, 2014
    Messages:
    7,650
    Looks to me like it could be some kind of light leak - stray light getting into the optics somehow.

    (Be aware that it could be infrared instead of visible light. Sometimes people install security cameras with a night vision mode - and they have IR illuminators built-in!)
     
  6. Stuart Gray

    Stuart Gray Standard User

    Joined:
    May 25, 2015
    Messages:
    7
    Thanks for all the responses so far. It was not an especially hot night when I took the image - around 20-25C and I have imaged quite successfully at those temperatures before. Iam not sure why there is a disparity between the set temperature and the chip temperature. I did try taking images at both -30C and 0C setpoints to see if there was some temperature dependence and waited for the camera to reach the setpoint each time. I saw the same effect at both temperatures.

    I most recently baked the desiccant in January. I have been doing it annually since I bought the camera and have not had any issues with condensation.

    I tried to take more images last night but there was a lot of cloud around and was not able to capture a decent light frame with the same conditions as the image in my original post. However, I was not able to reproduce the dark regions across the top and bottom of the image. I attached a bias, dark, flat and light frame though and will obviously try again when sky conditions are better to see if this happens again (this week is not looking good right now). These frames were captured using maximDL.

    I have not tried to look down the nose of the camera with the shutter open but can try to do so.

    With regard to light leak, the camera is fairly well shielded from most stray light when operating at night. My telescope is in a roll-off roof observatory and the walls prevent most light from surrounding houses and streetlights from reaching the camera. I have a dim red LED light on in the observatory when I am imaging and this was also on last night when I saw no effect. I was trying to image the same object so that the camera was in the same orientation.
     

    Attached Files:

  7. Stuart Gray

    Stuart Gray Standard User

    Joined:
    May 25, 2015
    Messages:
    7
    I am seeing this issue with the dark bands at top and bottom of my images again. It was especially noticeable while trying to take a new set of flat files last night and is generally more apparent in 2x2 binned images than 1x1 images. (See attached files). A 1x1 light frame taken with the same filter (red) from the previous night is also attached. I saw this with all my filters (L,R,G,B, Ha,O-III, S-II) and not just the red one.

    The flat files were taken with an electroluminescent panel fitted to the end of the telescope in an otherwise dark observatory at night with the roof closed.

    I have looked down the end of the scope but see no obvious obstructions. All I can see is the pick off mirror for the guide chip in the filter wheel but that is, of course, only on one edge of the chip and has been positioned to not interfere with the image. There is no evidence of it in the attached light frame.
     
  8. Stuart Gray

    Stuart Gray Standard User

    Joined:
    May 25, 2015
    Messages:
    7
    Took some additional test images tonight after posting the earlier message. I am seeing the dark bands in my light frames and also in the dark and bias frames. I also tried taking dark frames with my observatory open and closed to see if there may be some light leak as suggested above by Doug. I see the artifacts in the image even with my observatory closed which is also what I saw in the flat frames I posted earlier.
     

    Attached Files:

  9. mike m benjamin

    mike m benjamin Cyanogen Customer

    Joined:
    Jul 20, 2018
    Messages:
    118
    Gee that dark frame sure looks like the rbi preflash was running. That's what my STT-3200 looks like with the rbi selected.
     
  10. Colin Haig

    Colin Haig Staff Member

    Joined:
    Oct 27, 2014
    Messages:
    4,280
    Hi Stuart, my first inclination is a light leak or reflection somewhere in your optical path.
    To see if it is RBI, I suggest you try with CCDOPS or a demo of MaxIm DL Pro.
    Check that RBI Preflash is not being used. I suspect it may be ON, and SGP_ doesnt know how to turn it off.
     
  11. Doug

    Doug Staff Member

    Joined:
    Sep 25, 2014
    Messages:
    7,650
    Also to follow up on Colin's post, make sure your drivers and firmware is up-to-date. Use the SBIG Driver Checker for that.
     
  12. Stuart Gray

    Stuart Gray Standard User

    Joined:
    May 25, 2015
    Messages:
    7
    SBIG driver checker says that I am up to date.

    I took two 60 second dark frames using CCDops. One was taken with preflash and the other without. The one with preflash shows the pattern I saw in the previous images I posted.
    I then connected my camera to SGPro and checked my settings there. I have the flush count set to zero which is supposed to disable RBI (according to SGPro).
     

    Attached Files:

  13. Doug

    Doug Staff Member

    Joined:
    Sep 25, 2014
    Messages:
    7,650
    We did change the control mechanism for preflash a while back. Make sure SGPro is up-to-date also.

    Check if it works properly in CCDOPS.
     
  14. Stuart Gray

    Stuart Gray Standard User

    Joined:
    May 25, 2015
    Messages:
    7
    When using CCDOps, I see the dark bands across the top and bottom of the image with preflash on but they disappear when preflash is turned off. In SGPro I can turn preflash on but I am unable to turn it off. If I have turned preflash off in CCDOps then it stays off when SGPro starts up and I see normal looking images. Since this seems to be an SGPro issue I will follow up with Main Sequence Software. There is already a thread on their forum from someone with a similar issue.

    Thanks for your help.
     
  15. Doug

    Doug Staff Member

    Joined:
    Sep 25, 2014
    Messages:
    7,650
    We changed the way Preflash was enabled/disabled something like 4 or 5 years ago. It required the application software to be updated. Unfortunately it was absolutely necessary to make a "breaking change" for the function to work properly.
     
  16. Colin Haig

    Colin Haig Staff Member

    Joined:
    Oct 27, 2014
    Messages:
    4,280
    Mike - I did some digging, and it turns out there are a few other people who've experienced the RBI problem in SGP over the past few years. If the author of SGP needs help, have him contact us.
     

Share This Page