Resolved Odd artifacts in image

Discussion in 'Aluma Series' started by mike m benjamin, Nov 24, 2019.

  1. mike m benjamin

    mike m benjamin Standard User

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    I had my first light with my Aluma U694/FW8G attached to my Meade 70mm quad, as I am new to using Maxim it was a little bit of a rough start but I figured out enough to get guiding and take some test images. This is a 220s test shot using the supplied pro package red 36mm filter of the flaming star nebula (improperly labeled,lol) are seen in the lower left side are some odd reflections that streak. This shot was the worst example from last night (Moonless) my guess it's the filter causing this?

    Mike Benjamin
     

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  2. Doug

    Doug Staff Member

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    Looks like some sort of reflection. Might be a filter, but could also be something in front of the camera. There are some very bright stars in the area.

    Is it just one filter that shows that, or do all of them? Did you check the filters for damage or streaks (possibly picked up during installation).
     
  3. mike m benjamin

    mike m benjamin Standard User

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    Doug, here is a Lum of M42 from last night, same artifacts, not quite as bright or large either side of the satellite trail. I checked the filters closely upon install, they are clean.
     

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  4. Doug

    Doug Staff Member

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    Okay so that’s not from a star - it wouldn’t be in the same place. It’s not the camera either because that’s clearly something optical in nature.

    I’m now thinking it’s some kind of light leak. Can you post a picture of your setup?
     
  5. mike m benjamin

    mike m benjamin Standard User

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    Doug, here's a mock up from last night. I double checked the seams of the Filter wheel, camera and the M48 adapter, look tight, no gaps. The Meade has a camera rotator with M48 male threads. I used my STT-8300/FW8G setup on this refractor many times with no issues.
     

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  6. Doug

    Doug Staff Member

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    Very strange. I assume you do not get these on dark frames. How about if you cap the telescope and take a light frame?
     
  7. mike m benjamin

    mike m benjamin Standard User

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    Doug, I just finished a light frame test inside, I just capped off the dewshield and wrapped a black garbage bag on top using an elastic, left the inside lights on. Image looks fine to me, no artifacts.
     

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  8. Doug

    Doug Staff Member

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    Could you post raw, unprocessed FITS frames for the Horsehead and M42 images?
     
  9. Colin Haig

    Colin Haig Staff Member

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    Are the filters arranged shiny-side toward the telescope?
     
  10. mike m benjamin

    mike m benjamin Standard User

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    Colin, to my eye both sides were equally shiny and there's no markings either.
     

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  11. Doug

    Doug Staff Member

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    I'll note that "raw fits M42.fit" is actually the horsehead... but that's actually good. It is helpful have two different images of the same target taken with different filters (Luminance and Red).

    Conclusion: On those two frames, obviously guided to the same position, the reflections are identically positioned but different intensities. This rules out the filters. It's what you would expect to see if the rfelction was happening ahead of the filters.

    On the "raw fits flaming star.fit" image, the reflections are in completely different locations.

    Conclusion: It depends on what is in the field of view.

    This really looks like some kind of reflection in the optical path. I'm not sure what it's bouncing off of, but there's something somewhere ahead of the camera.

    Can you photograph the pick-off mirror in the FW8G from the front? I want to make absolutely sure it was installed correctly, and that there isn't a shiny spot on the tip of the mirror (it should be blackened).

    Another thing to try - make a donut-shaped temporary baffle out of cardboard and stick it in front of the filter wheel. See if that knocks out the reflections.
     
  12. mike m benjamin

    mike m benjamin Standard User

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    To me, the end does appear darkened.
     

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  13. mike m benjamin

    mike m benjamin Standard User

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    what about this undarkened area facing the filter Doug?
     

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  14. mike m benjamin

    mike m benjamin Standard User

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    Well as I had the filter wheel apart I decided to take a better look at the filters, there is a difference it can be noticed at the edges, one side has a coating to the edge and this side was chip side, so i flipped the filters and the sky was clear enough to try a few images. Honestly I don't see a difference. Flaming star was the worst offender and it's still bad. Funny though I did M38 an open star cluster with no nebulosity and there's just one dim streak in it.
     

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  15. Doug

    Doug Staff Member

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    It's not clear from the photo whether light from the telescope can actually hit it... but try this: take a sharpie and blacken it, and the tip of the mirror.
     
  16. mike m benjamin

    mike m benjamin Standard User

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    Doug, did better than that. I carefully taped off the surrounding area and gave it a shot of flat black. Guess what? Problem solved! I was suspicious when the artifact was long and thin in size and the unpainted backside of the prism was the same shape.
     

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  17. Doug

    Doug Staff Member

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    Great news! Good job and thank you for letting us know it worked out.

    We will look into improving the blackening of the mirror assemblies going forward.
     
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