Halo in Narrowband

Discussion in 'STX and STXL Series Cameras' started by bodda, Mar 9, 2016.

  1. bodda

    bodda Standard User

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    Hi,

    I first time try narrowband imaging

    We can see halo around bright stars, especially in O3

    My setup is AP 130GT STXL 11002M FWG8 Baader filter
    I have attach images
    The images are already stacked and the sub are 5minutes exposure

    Someone can help me?
    Thanks
     

    Attached Files:

  2. bodda

    bodda Standard User

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    I forget the S2 but it present the same halo same size than HA...
     
  3. Tim Puckett

    Tim Puckett Guest

    Are you running the system at F6.3? or with 2.7" telecompressor at F4.7?
    Are the mirror like surfaces of the filters located towards the sky in the filter wheel?

    You will have some halos on bright stars.

    If you can email me the fits file I can measure where the halos are coming from in the optical
    system.

    Cheers
    Tim
     
  4. Doug

    Doug Staff Member

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    They look rather like pupil ghosts, which happen when light reflecting off the sensor hits a concave surface and reflects back slightly out of focus. Focal reducers are a common cause, and are usually designed so that any ghosts are well out of focus so you can't see them. Of course any curved surface in the optical train can cause this; it's just more commonly encountered with focal reducers.

    The KAI-11002 is somewhat more reflective than some other sensors so any ghosts might be a little brighter than some other sensor types.

    You should inspect a luminance or red frame for similar ghosts. If they are faintly present then the root cause is the optical system, not the filter. Narrowband filters could possible make existing ghosts more obvious because of the darker background levels.
     
  5. bodda

    bodda Standard User

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    i m imaging at prime focus with astrophysics corrector not using focal reducer
     
  6. Doug

    Doug Staff Member

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    I'm not familiar with the design, but the corrector could easily be the source of the pupil ghost. If you can - experimentally - take an image without it, that would be very informative.
     
  7. bodda

    bodda Standard User

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    Hello,i ve done some calculationHalo 60 pixels so size on image 0.54mm SO like F/D 6.8 so distance 3.6mm
    ANd other halo 400 pixels SO distance 25mm
    I don't think that scope or filter are so close the CCD and i think that the CCD or the cover may cause those halo on images , maybe the coating defectuousdon't you thinkI hope an answer regards
     
  8. Doug

    Doug Staff Member

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    You can expect some reflection from coatings; none are 100% perfect. With very bright stars in a dark narrowband image this may simply be inevitable.
     
  9. bodda

    bodda Standard User

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    So nothing to do??
     
  10. Doug

    Doug Staff Member

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    I'm afraid not. These sorts of things can always be improved on by spending a lot more money, of course, but nothing can be made perfect.
     
  11. Dan Wilson

    Dan Wilson Cyanogen Customer

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    I had halos like that with my old Baader OIII filter. I switched to the Astrodon 3nm OIII filter (actually bought the whole set) and the halos were gone. Halos on the Baader OIII filter are pretty common.
     

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