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Delicious Donuts in my pictures.

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#1 Eyeheartmono

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Posted 22 September 2019 - 08:20 PM

I’m quite new to astrophotography and I’ve spent a couple nights in pretty light polluted skies trying to find some brighter objects to do some exposures on. I’ve had many instances where my pictures from my CCD ( DSI-IV ) have produced a large donut in the center of the view doing 30-45 second exposures. I’m trying to isolate what is causing it.

I thought it may be dew at first but my heater seems to be working well.
Maybe humidity?


Any ideas? When I figure out how to post pictures I will try and get one up.

Any help to a newbie would be appreciated.
Thanks in advance.

#2 Eyeheartmono

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Posted 22 September 2019 - 08:38 PM

north american nebula.jpeg

There we go



#3 OldManSky

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Posted 22 September 2019 - 09:01 PM

That's too big to be a dust donut.  Looks like a reflection.  Check to see if something in the imaging train (extension tube, adapter, etc.) has some shiny bits on the inside...


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#4 Eyeheartmono

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Posted 22 September 2019 - 09:05 PM

Hmm, I’ll check that. You say reflection, could this be from the moon? My scope was pointing almost at the zenith when I took these pictures and the moon was just rising at about 15 deg on horizon.



#5 RogeZ

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Posted 22 September 2019 - 09:07 PM

it looks like a big spot of water, covering the optics...



#6 OldManSky

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Posted 22 September 2019 - 10:56 PM

Hmm, I’ll check that. You say reflection, could this be from the moon? My scope was pointing almost at the zenith when I took these pictures and the moon was just rising at about 15 deg on horizon.

If you have a dew shield, probably not.

But if you have a light leak somewhere in your imaging train...maybe!



#7 Adun

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Posted 22 September 2019 - 11:14 PM

My vote is for wormhole exit point.


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#8 Eyeheartmono

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Posted 23 September 2019 - 08:50 PM

Here are pictures of my image train, other then there being some debris on my diagonal I can't see much else wrong with it as it is rather new. Maybe i'll try putting a garbage bag over the image train to see if light is entering next clear night.I know the diagonal is probably the worst thing to have the camera attached to but it was the only thing i had to let the camera come in focus at the moment till some spacers arrive.

 

pic1.jpg pic2.jpg

 

 



#9 RogeZ

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Posted 24 September 2019 - 06:01 AM

You need to remove the diagonal and set the camera straight on the scope. Try that combination.

#10 happylimpet

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Posted 24 September 2019 - 06:11 AM

I strongly suspect dew somewhere in the optical train....Ive seen it before many times on CN and this looks just the same.



#11 Eyeheartmono

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Posted 24 September 2019 - 06:29 AM

Thanks for the help everyone, as i said before i know the diagonal is not optimal  and spacers are in the works. I was having an issue with back focus.

Would wrapping another heater around the back of the OTA help? My only concern is trapping heat inside the optical train and in turn fighting with the cooling of the CMOS chip.



#12 geneva_min

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Posted 24 September 2019 - 07:29 AM

I'm not giving advice on this.....I'm more asking.  Wouldn't flat calibration frames remove the issue regardless of what's causing it?



#13 Eyeheartmono

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Posted 24 September 2019 - 08:22 AM

I don’t think flats would remove dew on the sensor if that’s the case. That picture actually is about 20x 30 second exposers plus 10 dark frames. The ring was actually quite worse in individual frames.

#14 Eyeheartmono

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Posted 07 October 2019 - 10:55 AM

If anyone was wondering this was a user error, I moved the dew heater farther up the dew shield and it fixed the issue. Thank you for the help!

 

northamerican new.jpg

 

 




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