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Artifact in images

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#1 Don Marcotte

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Posted 26 July 2021 - 09:53 PM

I'm hoping someone can help me. I live in a Bortle7/8 urban area and have to use narrowband filters. Over the past few nights, under 90%+ full moon, I've gotten the artifact shown in the attachment. I believe it has occurred without the moon being present but I have not checked.

 

Gear - ASI1600MM, CEM25P mount, 100ED with .75FR, ASIair Pro, Starizona filter slider, 1.25" 6nm Astronomik Ha, Oiii and Sii filters

240sec subs, unity gain, binned 2x2, sensor temp -20°C 

 

All lights in the immediate area of my strata unit were turned off for the last couple of nights but the Ha session only had one neighbor's light turned off.

 

The target was NGC7380, the Wizard.

 

I've tried to ensure there was no sag in the optical train. I could see no obstacle in that path.

 

Suggestions?

 

Don

Attached Thumbnails

  • NGC7380O 210725 b2 artifact.jpg


#2 Tapio

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Posted 27 July 2021 - 04:01 AM

This is left of NGC 7380 (and only a crop). I assume it's circular in full image.

Don't know if it's moon to blame as it's not nearby.

Bright(ish) mag 3-4 stars in Cepheus (Del Cep and Zet cep) - maybe.

But it's most likely caused by some shiny surface in some component in optical train - in filter, filter slider, focuser, fr.

You could remove camera and shine a torch in fron and see if you can spot something shining.

 

Did this came out with all filters ?



#3 Don Marcotte

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Posted 27 July 2021 - 11:34 AM

It is present with all 3 filters. At first I thought it was only Ha but realized later that it was also present with the other two, just fainter.

 

One thing I forgot to mention is that it is present also with my Nikkor AF300/4 lens.

 

Don



#4 Deesk06

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Posted 27 July 2021 - 11:43 AM

Looks like it could be internal reflections or a light leak. If it is happening with all cameras and filters it is most likely not a dust mote as the lens cells would be too far out of focus to see this. Have you check for any light leaks? If not then go into a dark room and shine a flashlight around your setup while on video or taking an exposure and see if you come up with anything.

 

Also double check the filter drawer is seating correctly. 

 

Just some ideas, lets see what others have to say as well. 


Edited by Deesk06, 27 July 2021 - 11:43 AM.


#5 mdavister

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Posted 27 July 2021 - 01:17 PM

Reducer

 

I had a similar artifact coming from the back edge of my Reducer/Flattener. Painted it flat black (it was glossy black from the factory).



#6 Don Marcotte

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Posted 27 July 2021 - 01:36 PM

Mitch - it also happens with a Nikkor lens so it isn't the AstroPhysics FR. I agree with your assessment that it is a reflection from somewhere.

 

Deesk06 - I have seated my filter carefully and it is flush with the unit. But the Starizona filter slider does have a light leak. So I covered the filter holder with electrical tape. That being said, I'm seriously considering replacing the filter slider with my ZWO electronic filter wheel. Secondly, the slider is attached to my ASI1600 via an 11mm M42 F-F adapter. I could have attached it directly to the camera like the EFW does.

 

It has been remarkably clear this summer in the Vancouver BC area. The rest of the province inland is suffering from 250-300 of forest fires at any one time. That certainly ruins the night sky for most inland residents of BC and anything east of it. Because of my good fortune I won't want to waste a moment capturing photons. This, being the Pacific northwest, means perpetual clouds from November through March.

 

Thanks for the comments from both of you.

 

Don



#7 Don Marcotte

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Posted 29 July 2021 - 01:18 PM

Update - I switched to my ZWO Electronic Filter Wheel and the artifact still appears.

 

Where do I look next?

 

It appears  with:

  1. lens and scope;
  2. ZWO EFW and Starizona filter slider;
  3. local lights on and off;
  4. Ha/Oii/Sii filters
  5. FR present or not

All connections are tight. There doesn't appear to be any light path sag.

 

I'll take some darks in daylight and see what happens.

 

Don



#8 Don Marcotte

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Posted 30 July 2021 - 05:34 PM

Last night I captured images with Ha (accidentally) and Sii. I turned off my neighbors' lights inside my strata. The artifact did not appear. However, it was there when I used my Oiii filter the night before. That suggests it is an external light source which is causing the problem. However, it occurs even when all the nearby lights are off.

 

There may be one explanation - the moon. I have been shooting with the moon at 100% full, +/- 30%. Why it would only affect Oiii is unexplainable.

 

Don



#9 dswtan

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Posted 30 July 2021 - 09:45 PM

There may be one explanation - the moon. I have been shooting with the moon at 100% full, +/- 30%. Why it would only affect Oiii is unexplainable.

Sorry, but the moon particularly impacting OIII is kind of a "known issue" that's been reported on CN before. Not trying to be smart here, just empathizing!



#10 Don Marcotte

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Posted 31 July 2021 - 12:51 AM

Sorry, but the moon particularly impacting OIII is kind of a "known issue" that's been reported on CN before. Not trying to be smart here, just empathizing!

Thanks. You wouldn't happen to have a link? I searched without success.

 

Don



#11 Don Marcotte

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Posted 04 August 2021 - 07:16 PM

Follow-up report. The moon was definitely the artifact  source for most of the sessions with a problem. A light leak in my Starizona filter slider caused problems on other occasions. However, even with the moon being absent, there is still a problem with Oiii captures. Something in my neighborhood is a problem. It might be my neighbors green patio light which I did not turn off.



#12 Don Marcotte

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Posted 17 August 2021 - 12:34 AM

The source of the artifact is damage to the ASI1600's sensor. Last year the camera came loose from the scope and crashed onto patio stones. It seemed to work fine but an artifact showed up at times. There is damage to the sensor in two spots along one edge. You can't see it until you hold it at a very specific angle.

 

I had isolated the problem to the point where the only common denominator was the camera. A friend then suggested that I check the sensor

 

I have left a message in the ZWO cameras forum asking for a repair service.

 

Don




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