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Problem with "Halo" within Newton Telescope...

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#1 TheAviator

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Posted 22 August 2019 - 02:56 AM

Hello,

 

I am working with a Skywatcher Newton 200/1000 f5, a ZWO ASI1600MM-C, ZWO EFW, and Baader MPCC and I do

get a strange looking Flatframe and the same reflection is visble as well withing the lights.

I do capture the flats with SGP, a Lacerta Lightbox and a white t-shirt inbetween lightbox and telescope.

I do run the SGP Flats Calibration Wizard, set it to 14000ADU +-500 and timing between 0.02s-8s

 

Have anyone encountered the same "halo"?

I also attached some black vinyl patches within the Skywatcher and the imaging train, but the halo is still

visible.

Again, it is visible during taking lights and Flats.

Hope anyone has some solution..

Thank you

Attached Thumbnails

  • MasterFlat_ISO0.jpg


#2 zach540

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Posted 22 August 2019 - 03:40 AM

Do you have any spacers between the MPCC and the EFW/camera?  According to Agena Astro "The MPCC is designed for a nominal 55mm distance from the mounting flange to the film plane."

 

If you don't have any spacers, here's what ZWO recommends using:

Cooled-Mono-Camera-solution.jpg



#3 james7ca

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Posted 22 August 2019 - 03:42 AM

All I can see is something that looks like standard vignetting, which is what flats are supposed to correct. However, the JPEG compression used for the upload to CN is causing some posterization which may be masking what you are referring to.



#4 Frabog

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Posted 22 August 2019 - 04:16 AM

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#5 TheAviator

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Posted 22 August 2019 - 05:56 AM

I am using spacers to get to 55mm, yes.

Vignetting was my first idea as well, but I do use other lenses as well, and the vignetting is way smaller.
While using the Newton the halo or vignetting is very prominent!
And trying using Flats and Darks and somehow managed
The halo, but it is hard work...

#6 james7ca

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Posted 22 August 2019 - 06:56 AM

You can probably calculate the amount of fall off that would be expected given the size of the secondary in your scope. If the secondary is too small you could have problems covering the frame of the ASI1600. I'm not saying that I know that is the problem, but it would be worth checking just to be sure. The diagonal on the ASI1600 is just over 22mm.

 

According to this website for an 200mm f/5 mirror and a secondary to focal plane spacing of 152mm (two inches outside of the edge on the primary mirror) you need a secondary with a minor axis of 50mm to fully illuminate a field that is 22mm in diameter.



#7 TheAviator

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Posted 22 August 2019 - 08:29 AM

aha, this maybe why I am getting reflections of my primary mirror within my images.

When centering on a bright star, I do get a huge halo of the primary mirror showing the spikes of

the secondary "spider". not the spikes at stars, but black "areas" within the halo of the primary reflection...

 

thanks james!

so my secondary mirror is too small...



#8 james7ca

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Posted 22 August 2019 - 09:42 AM

aha, this maybe why I am getting reflections of my primary mirror within my images.

When centering on a bright star, I do get a huge halo of the primary mirror showing the spikes of

the secondary "spider". not the spikes at stars, but black "areas" within the halo of the primary reflection...

 

thanks james!

so my secondary mirror is too small...

Possibly, but you should go to the website I linked above and see how much fall off you should see given the spacing and size of your secondary. You probably don't need 100% illumination, but if the secondary is particularly small that could be a problem for your camera (but still, it should be mostly correctable with flats).




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