Resolved SBIG 16803 - RBI

Discussion in 'STX and STXL Series Cameras' started by Niall MacNeill, Jun 24, 2020.

  1. Niall MacNeill

    Niall MacNeill Standard User

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    Hi Colin, Doug,

    As I await the water cooler for my camera, I continue to do trials to optimise my configuration and get set up to image with SGPro.

    I am happy to say that I have auto-focussing and PHD guiding working and have run a number of sequences successfully. As you know there is a little bit of setting up to get all the bits talking together.

    However, out of blue recently I suddenly started getting curved stripes across the images, which seemed to be worse with bright objects, or indeed when the Moon was out. I can do the trials when the Moon is bright because I am not intended to use the images. At first I thought these were reflections and something to do with the OTA. However, when I rotated the camera 90 degrees, the pattern stayed in the same place indicating it was within the camera.

    NGC 523605 29 20201x1-20.20C180.000secsLuminanceLight00000008.jpg

    Further investigation and indeed some help from an experienced astronomer friend told me that these are RBI. The pattern is entirely consistent with images I have seen where this problem is manifest.

    I am unclear as to why this suddenly started occurring, although I have a theory as elucidated below.

    In any case I need to resolve this before the water cooler arrives.

    SGPro has the ability to do an IR flash. I had set this to a 5 sec Flash and a Flush count of 1. However, in all honesty I didn't really know what I was doing and this was obviously ineffective. My friend subsequently suggested 0.5 sec Flash and a Flush count of 5.

    In hindsight it may have been my commissioning of SGPro that created the problem in the first place, if I was having a long Flash and insufficient to discharge it. What do you think?

    Screen Shot 2020-06-24 at 11.33.11 am.png

    Can I ask you for any advice on this matter, particularly the settings. It has also been recommended that when using RBI I should operate at a lower temperature to overcome the noise created and that the Darks have to be captured the same way. Please advise.

    Thanks,

    Niall
     
    Last edited: Jun 24, 2020
  2. Doug

    Doug Staff Member

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    That pattern is caused by RBI preflash.

    RBI problems happen when a bright star injects photoelectrons deep into the substrate, underneath the pixels. It then leaks out slowly and contaminates the subsequent exposure(s). So a faint image of the star appears on subsequent images.

    If you preflash you get maximum RBI absolutely everywhere across the chip. Then the camera flushes out what it can before it starts the exposure. You get those circular patterns, which are basically images of wafer polishing marks that were generated during sensor manufacturing. Then when you also RBI preflash for your dark frames, the patterns subtract out. RBI mitigation adds some extra photon shot noise, but any RBI effects from bright stars in your previous image are swamped out.

    If your controls say RBI is off, but it isn't, then some software component is out of date. Some years ago we made necessary changes to the RBI controls in the driver, and the firmware, drivers, and control software all needed to be updated to ensure everything works properly.

    You should make sure your software, drivers, and firmware are all up-to-date. Download the latest SBIG Driver Checker and use that to update drivers and if necessary the firmware. Also update your control software to the latest build.
     
  3. Niall MacNeill

    Niall MacNeill Standard User

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    Thanks Doug, that's what I figured.

    Are you saying that if I turn the pre-flash function off altogether in SGPro, the problem will go away?

    The is not my screen shot, it is from the SGPro website. As I said, when I set up SGPro, I put some settings in there....5 sec pre-flash and 1 flush.

    Or is it likely that I will run into problems with bright objects in the FOV in the future and will need to adopt the RBI pre-flash, with adequate flushes to ensure ghosts don't appear in subsequent images? Clearly if that is the case I will need to use exactly the same settings for the Darks.

    Thanks, Niall
     
  4. Doug

    Doug Staff Member

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    Your options are:

    1. Turn off RBI Pre-Flash

    2. Turn it on, but shoot your calibration frames with it on, also

    If you don’t take your light frames and calibration frames in the same mode, you will see the swirl marks.

    I recommend leaving it OFF except when imaging a field with extremely bright stars in it, and even then only using it if RBI is actually causing trouble. Otherwise you are adding noise for no advantage.
     
  5. Niall MacNeill

    Niall MacNeill Standard User

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    Thanks Doug, that is what I thought.

    How will I know how bright I can have the stars in the image? Will the circular arcs be manifest if they are too bright which will tell me I need to apply the Pre-Flash? OR will I see ghost star images if dithering?

    Would you say an image of Omega Centauri for example would require the RBI Pre-Flash.

    Thanks again,

    Niall 50mm Adaptor no spacer_NGC 513906 20 20201x1-19.13C120.000secsRedLight00000002.jpg
     
  6. Doug

    Doug Staff Member

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    RBI is only a problem if you over-saturate the sensor. Your Omega Centauri image does not saturate the sensor. Having Alpha Orionis in the field will definitely saturate it.
     
    Niall MacNeill likes this.
  7. Niall MacNeill

    Niall MacNeill Standard User

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    Thanks Doug, that is most helpful.
     
  8. Niall MacNeill

    Niall MacNeill Standard User

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    Hi Doug, I need your help again.

    I turned off the RBI pre-flash in Sequence Generator Pro.....or thought I had. However, the images I produced had the self same RBI arcs. I wondered if the sequence I had set up had used the IR pre-flash thus creating the pattern. The next time I imaged, a few days later, the camera had been up to room temperature in the meantime and I presumed any RBI would have dissipated. This time I imaged with The Sky X Camera Add-on to be sure that no RBI pre-flash had been applied. To my chagrin, the arcs were still there bold as brass. I had imaged for 3 mins and there were no bright objects at all in the field of view. How can that be happening?

    So it seems, that prior to using SGPro, I never had these arc pattern in my images. I started commissioning SGPro and in my ignorance I set the RBI preflash and a single flush. The pattern suddenly appeared in my images. It seems that ever since then, the pattern is there, even when I have specified no flushes, which should have disabled the pre-flash. It is almost as if SGPro has set some switch on the camera such that the pre-flash is still occurring for each image.

    Can you shed any light on this and give me some advice as to how to avoid the RBI arcs in my images? As we discussed I would prefer not to do RBI pre-flash, unless I am imaging particularly bright objects.

    Thanks,

    Niall
     
    Last edited: Jul 19, 2020
  9. Niall MacNeill

    Niall MacNeill Standard User

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    So I thought I would try connecting to the camera with CCDOps, to see what I can learn about settings and whether by default RBI pre-flash is one of the settings. As soon as I tried to connect to the camera, the program crashes......It happened multiple times. I have a direct cable to the camera, no usb hub. The camera connects perfectly well to the Camera Add-on on the SkyX. So I redownloaded the SBIGUDrv and CCDOps and tried it again. It thinks about it for about 10 seconds and then.....gone. No error message, nothing....it just disappears. I relaunched CCDOps several times and the same result each time. I note that there are a number of forum posts about this and I didn't see anything there that was particularly illuminating.

    I presume I need CCDOps to work so I can see all the settings. Can you let me know how I can get this to work please?

    Thanks again,

    Niall
     
  10. Niall MacNeill

    Niall MacNeill Standard User

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    So after downloading the latest SBIG Driver Checker and updating all the drivers and firmware that I am aware of, I set up to take a dark image of 3 mins duration. The camera has not been touched since yesterday and was at 20C during the day.

    This is the result Test image RBINoTarget07 19 20201x1-19.98C180.000secsRedDark00000001.jpg

    Clearly an RBI pre-flash is now being applied to each image.

    Can you please tell me how to turn it off?

    Thanks,

    Niall
     
  11. Doug

    Doug Staff Member

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    What software are you using to run the camera?
     
  12. Niall MacNeill

    Niall MacNeill Standard User

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    I have used both the Camera Add-on for The SkyX Professional and Sequence Generator Pro. As I mentioned I never had a problem with the SkyX and there don't appear to be any RBI pre-flash options with it. However, I am converting over to SGPro and there is an option there to enable or disable RBI pre-flash. Having enabled it once, it doesn't seem to be disabled when I set the flush count to 0, where the mouse-over says that it will be disabled by doing this. Furthermore when I go back to The SkyX to do imaging the preflash seems almost certainly to now be occurring by default.
     
  13. Doug

    Doug Staff Member

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    Make sure your drivers and firmware are up to date via SBIG Driver Checker.

    Try it with MaxIm DL - see if it can control the RBI setting properly.
     
  14. Niall MacNeill

    Niall MacNeill Standard User

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    I did. They are up to date. Any idea why CCDOps falls over?
    OK I will download MaxIm DL and try that.
     
  15. Niall MacNeill

    Niall MacNeill Standard User

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    I have requested the demo.
     
  16. Niall MacNeill

    Niall MacNeill Standard User

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    I have discovered the problem. There is a bug in SGPro.

    Once you turn RBI flash on, it stays on, for imaging with both SGPro and The SkyX. Since the function to disable RBI pre-flash in SGPro doesn't work and The SkyX Camera Add-on has no functionality in that area, once it was set there was no way of turning it off and so every image I produced from the day I turned on the pre-flash in SGPro has had it applied.

    Here is the detail of the trials I made to prove this.......

    After your suggestion Doug, I downloaded the trial version of MaxIm DL and as I'm sure you know it has an option to capture “Raw” and another for “Raw + pre-flash”. I selected the former and produced darks without the pattern. I then turned the pre-flash on with the default of a 4 sec flash and 3 flushes. This produced the pattern. I then went back to “Raw” and took a series of images over a half an hour watching the pattern fade away.

    I then went to The SkyX and took a dark with no pattern.

    Next over to SGPRo and again, having selected zero flushes (i.e. no RBI), I took a dark, with no pattern. I then turned on the pre-flash and got the pattern as expected. I then set the number of flushes to zero again and this is supposed to effectively turn pre-flash off. However, as I took images over the next 3/4s of an hour they did not fade, indicating the pre-flash was still being applied.

    I then went waited a half hour before going back again to Maxim DL, set it to “Raw” i.e. no pre-flash and took a dark. No pattern. I then turned pre-flash back on which gave the pattern.

    I then went back to The SkyX and after waiting half an hour I took another dark. The pattern would have faded away in this time, but no, it was there bold as brass. This proved that the flag to initiate the pre-flash, as set by MaxIm DL was still being applied....The SkyX has no capability to change that.

    So in summary, once I turned on the pre-flash in SGPro, it simply stayed on despite my having set the number of flushes to zero, which is supposed to turn it off. The SkyX Camera Add-on, has no RBI pre-flash input and so it seems that when it is used the last setting is applied. It wasn’t until I download Maxim DL and set the option on Raw that the pre-flash was finally turned off.

    Unbelievable.
     
  17. Doug

    Doug Staff Member

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    Thanks for reporting back. Hopefully the third party software providers can resolve the problem for you.
     
  18. Niall MacNeill

    Niall MacNeill Standard User

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    I hope so too Doug, thanks. I have raised a forum post.

    I also discovered last night when doing Flats through SGPro, that I could set the first 5 positions of the Filterwheel, 1) Luminance, 2) Red, 3) Green, 4) Blue and 5) Ha. But when I went to set 6) OIII and 7) SII it didn't work. They seem to only offer the STX-5 filter well option, which out of necessity I had selected and not the STX-7 Filter Wheel that I have, so that is likely the reason.
    Am I the only one who has ever used this camera/ filter wheel combination with SGPro?
    When I went back into the The SkyX, where there is an option to select the correct filter wheel, I was able to set it to OIII and SII and when I did so and went back to SGPro, it reported the correct filter.
    However, when I did the Flats on full power with my light box I got the following times to achieve a 65% of maximum ADU. All except Luminance were taken at full light box power:
    1) Luminance......2 secs fully saturated and I needed to wind the rheostat back to get the 40,000 ADU in 2 secs
    2) Red......3 secs
    3) Green......11 secs
    4) Blue.......36 secs
    5) Ha.......30 secs
    6) OIII......200 secs
    7) SII.......23 secs

    I was very surprised that the Blue was so long and that RGB were so different to each other. I was equally surprised that Ha only required 30 secs when OIII required 200 secs.
    I am now concerned that SGPro is not only unable to select OIII and SII but is possibly electing the wrong filters.

    I could try this with MaxIm DL and also perhaps remove the FW cover and watch which ones are being selected by the program. Any other ideas?

    Is it just me?
     
  19. Doug

    Doug Staff Member

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    I don't know. We don't tend to hear about problems with third party software products, except when the user thinks it's a camera problem. ;)
     
  20. Niall MacNeill

    Niall MacNeill Standard User

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    They recommended I select "Auto detect" for the FW and that seems to have worked. They are however going to add the the FW7-STX as an option, which is obviously more comfortable for the user than hoping that an auto detect option works.
    Thanks Doug.
     

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