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Old 22-11-2015, 03:15 PM
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Ryderscope (Rodney)
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Reflection or Rubbish?

I have an artifact on my Red filter subs that has appeared with my current image project (M45 - Pleiades). See attached jpeg of a red sub along with a crop of the corner where the artifact can be seen. Lens was my EOS 200mm prime and camera the QSI683-ws8.

The artifact was not there on the subs from my previous image project (Fornax galaxies). The lens has been removed and replaced since my last image and I made sure to use a hand puffer to blow out any dust before replacing the lens.

I took a set of flat frames prior to starting the image capture for this project and a copy of the same corner on the Red sub flat is also attached to this post. As you can see there is no apparent artifact on the flat frame.

So before I go and start pulling my filter wheel apart I was wondering what the consensus would be as to whether this is some rubbish that has found its way into the filter wheel or if it might just be some sort of reflection phenomenon.

The images as they appear below from left to right are:
- One of the Red subs
- A crop of the bottom left corner of the Red sub
- A crop of the bottom left corner of one of the Red flat frames

Subs exposure time = 300s

Thought of others on this would help.

Thanks for looking.

Rodney.
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Click for full-size image (Flats_6sec_R_20151117_214502_crop.jpg)
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  #2  
Old 22-11-2015, 03:39 PM
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RickS (Rick)
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Looks like a reflection or other stray light, Rodney. If you had a foreign object on the filter it would show up as an out of focus shadow (like dust motes appear as donuts.)

There's a fairly bright star just outside your FOV at the bottom left that's probably the cause.

Cheers,
Rick.
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Old 22-11-2015, 04:46 PM
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Ryderscope (Rodney)
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Thanks Rick, I like that answer as it saves me pulling apart my filter wheel
Its a bit suspicious as well given the semi circle shape.
I might try shifting the object a little to see if this makes it go away.
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Old 22-11-2015, 07:25 PM
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Reflection. You have something that is a bit shiny in the imaging train.

Look down the lens with a torch and see if there is something shiny.

You can also make a baffle out of some thin black cardboard and tape it to the lens hood to stop it down a tad. Or get a large step down ring and use it as a baffle.

Or try moving the view slightly. It'll be a bright out of field star. Move the view a bit and it may disappear.

Greg.
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Old 23-11-2015, 07:52 AM
cfranks (Charles)
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I have the same problem with a 105mm Takumar 6x7 lens with a bright star in the FOV. I thought mine was poor(ish) quality AR coating. Strange they both appear in the cornet of the image.
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