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#1 BKMaynard

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Posted 27 September 2021 - 11:13 AM

I apologize for posting a problem I've seen here many time on the subjects of light leaks with a newtonian scope. I've read all the post on this subject. I've remedied all the possible issues. I've examined every possible cause but I'm all out of ideas. A wicked gradient in all my images with my new ASi 2600mm and 8" newt in every image. You're my last hope of finding where this is coming from. Here's what I know:

 

Scope and camera have been thoroughly inspected and masked for every possible light leak from the back of the primary mirror to the end of the focuser. Visual inspection of inside the ota is jet black with only the primary and secondary visible. Absolutely no extraneous light visible from anywhere.

 

Dark frames look perfect, no bright areas at all. Same with flats, perfect. Calibration is working as its supposed to meaning all vignetting and dust are corrected. Image looks good except for the severe, stray light that's always in the same spot, and runs at the same angle in all my images.

 

I have one image for an example. The obvious issue is exactly the same in every image I take. This image is 5 minute Ha subs. Shorter RGB subs show similar results but interestingly I'll get a red streak, green streak and blue streak instead of one color streak of light.

 

Thanks for your thoughts

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  • ha_clone_2.jpg


#2 elmiko

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Posted 27 September 2021 - 11:31 AM

You mentioned everything checked for light leaks from the primary to the focuser. What about between the focuser and your camera? Looks like a light leak in the imaging train. Possibly the filter wheel.


Edited by elmiko, 27 September 2021 - 11:33 AM.

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#3 OldManSky

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Posted 27 September 2021 - 11:32 AM

Well, if it's in the same spot no matter what the target, then it's like not a streetlight or porch light or bright star just outside of the frame.

Which leaves the camera and/or equipment on the scope.

So...what's DIFFERENT when you're taking lights vs. darks/flats?  Identify what's different, then check those to see what's going on.  It could be something as simple as a red LED on some piece of equipment that doesn't get through when the front is covered (for darks and flats)...


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#4 BKMaynard

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Posted 27 September 2021 - 11:38 AM

 

You mentioned everything checked for light leaks from the primary to the focuser. What about between the focuser and your camera? Looks like a light leak in the imaging train.

Thank you for your response. I put a shroud around my focuser and camera. Zero light leaks there. I know that's usually the area where most people get problems from so I was sure to seal all that up.


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#5 rgsalinger

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Posted 27 September 2021 - 11:54 AM

I had a similar issue with my QHY600. The problem was that light was leaking around the filters because there were just a tiny bit smaller than the 2" filter holders in the carousel (CFW3-L wheel). I never saw it in the darks, but I did see it in the flats if I stretched them. I had my 50mm Ha and SII filters changed to a 2" filters and the problem disappeared. I never saw it with my other filter.

 

Are you certain that you don't see any gradient (stretch them) in the flats? I needed to stretch mine to see what was going on. 

 

One other possibility is some kind of dew getting into the system. The final issue that's been reported with ZWO camera is that some kind of oil leaks out onto the frame but the threads I've seen don't look like what you are getting. 

 

Rgrds-Ross


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#6 Apollo XX

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Posted 27 September 2021 - 12:09 PM

Have you tried rotating the camera to see if the streak follows the chip orientation? Then you'd know if the problem was at or before the camera.

Mike

#7 RazvanUnderStars

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Posted 27 September 2021 - 12:26 PM

If the problem follows the chip orientation, could it be a thermal artefact (unequal cooling of the sensor) rather than light? Also, are the optical surfaces inside the camera (sensor, filter) clean and uniform when inspected?



#8 BKMaynard

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Posted 27 September 2021 - 01:03 PM

 

If the problem follows the chip orientation, could it be a thermal artefact

You may be on to something here. The gradient stays in the same spot no matter the camera orientation. I wondering if the dew heater in the camera may be causing the problem



#9 BKMaynard

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Posted 27 September 2021 - 01:13 PM

Thanks for the feedback guys. All of you are most helpful. I see I have a few more things to look at.



#10 Der_Pit

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Posted 27 September 2021 - 01:21 PM

Did you check the tilt plate of the camera?  ISTR there had been some issue at some point.  I'm not using mine, so I never investigated further...



#11 BKMaynard

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Posted 27 September 2021 - 02:23 PM

Thanks, I'll give that a check



#12 Monkeybird747

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Posted 27 September 2021 - 06:46 PM

Look through the filter wheel at the sensor while taking an exposure and make sure the filter wheel isn’t doing something wonky during the exposure. It almost looks as if the filter wheel started to move at the end of exposure, or was still moving when the exposure began. Is the wheel set to bi-directional or unidirectional rotation? Don’t get too discouraged. Something that egregious will reveal itself eventually.

 

If you need to, start pulling parts one at a time and take an image and see if you can narrow it down. Pull the filter wheel and try an image. Check the filter gaps as others have mentioned. There are filter masks available that prevent light leaking around the filter. Make sure nothing on the focuser or coma corrector is intruding on the light path inside the tube when in focus.

Hang in there!

 

MB



#13 BKMaynard

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Posted 27 September 2021 - 08:34 PM

 

Did you check the tilt plate of the camera?

BINGO!!!  Light leak from tilt adapter. Even though the plate is flush and un adjusted, that little leak of light was squeezing through. 


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