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Old 10-10-2020, 09:49 AM
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help with circular artefacts - filter reflections or?

hi all, i've only recent got back into imaging but have done a lot of images the last couple of months. Last night I decided to add a couple hours data to a Helix set from a month ago, but this one using an Optolong L enhance 2in filter. Previous was IDAS-LPS-P2.

The attached jpeg I've deliberately over stretched to show the artefacts which appear as perfectly round light spots about the same size as the helix. These weren't in the original dataset so must have been introduced last night.

I've used the l enhance for a few weeks now and haven't seen this on any other images.

I'm using espirit 100ed and it's flatenner, a filter draw and ZWO extensions to an ASI533mc camera.

Anyone know what this is and more important how can it be avoided?

many thanks
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Old 10-10-2020, 10:04 AM
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or dew?

actually one other possibility just occured, I just recall there was a large circular patch of dew on the centre of the lens this morning. I close up and tarp covered after finishing last night. Assumed that built up after covering, but I guess could have been there during the evening....may not have had the dew zapper as fired up as needed?
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Old 10-10-2020, 10:34 AM
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and answering my own question further, I also posted on cloudy nights and got a bunch of confident replies, that thems is dust mote effects and good flats will fix... I do use flats, but was lazy and used from a previous night. Camera hasn't moved but new dust could have appeared and focus was a tad different I expect. I hope that's it as it's a very easy fix :-)
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Old 10-10-2020, 10:55 AM
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Hi Robert

Flats should get rid of them.
Occasionally I remove the camera and wipe (dab) the lens gently with a clean glasses cloth. Breath some moisture onto the surface if you need.

Do this under strong light and you may see the dust particles.
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Old 10-10-2020, 11:17 AM
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thanks peter, yes the main problem seems to be I used the wrong flats... from several nights earlier (doh)... just tried again briefly a re-run using flats from the night before (no camera movement in the interim) and motes be gone ...I am very happy with that!
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Old 10-10-2020, 05:05 PM
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and here's the result with better flats used

no more motes :-)
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