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Old 01-01-2021, 01:12 PM
MarkInSpace (Mark)
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Collimation issue? egg stars?

I seem to have issues with egg shaped stars in the upper right and upper left corners of my images.
I am using a SkyRover 115 triplet with the recommended flattener and an ASi294MC Pro camera.
Could my focuser be out of collimation with the front lens?
Any thoughts about the cause and cure would be gratefully appreciated!
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  #2  
Old 01-01-2021, 02:45 PM
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Joshua Bunn (Joshua)
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Hi Mark,


It appears it's a collimation issue or tilt issue as the distortion is not even over the field. Can your scope be collimated? As for the focuser mechanical axis not being aligned with the telescope optical and/or mechanical axis, you could test that by placing a laser in the focuser drawtube and making sure it hits the center of the lens cell, assuming the lens cell is centered in the telescope tube.


regards
Joshua
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Old 01-01-2021, 03:25 PM
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xa-coupe (Jeff)
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If the eggs were all around I's suggest back focus, but just in the upper parts is weird. I'll be interested to see if someone has a fix.
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Old 01-01-2021, 04:26 PM
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This is tilt. You can see nicely focused stars bottom left but blurry and distorted top left and to a lesser extent top right.

Source of the tilt could be yr sensor, an adapter, the focuser.
Don’t monkey with the lens, its not the problem.

Get some spark plug feeler gauge and pack out the Bottom right of your camera looking at it from behind. That will correct the top left.
Its probably needs around 0.05mm packing.

Do that, retest and let me know the result. The top right may need a smaller amount packed out on the bottom left looking at the camera from behind.

There you go I just saved you a potential
major headache!

Greg
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Old 01-01-2021, 04:36 PM
MarkInSpace (Mark)
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Thanks for that, Greg!
Unfortunately, I have to admit, I don't understand how to do what you suggest.
The camera screws in, so how do I pack it?
cheers
mark
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Old 01-01-2021, 07:39 PM
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Joshua Bunn (Joshua)
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Greg's suggestions are good advice, although you may need to experiment with what side of the camera equates to what side of your downloaded image. Greg's suggestions would be right for a cassegrain type telescope, but it might be different for a refractor type telescope.


With regards to image train tilt, is there any other place where you could adjust for tilt by placing shims somewhere?


Josh
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Old 02-01-2021, 07:23 AM
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Quote:
Originally Posted by MarkInSpace View Post
Thanks for that, Greg!
Unfortunately, I have to admit, I don't understand how to do what you suggest.
The camera screws in, so how do I pack it?
cheers
mark
In between the camera body
And the filter wheel is where I put it.
As Josh said I have assumed you are using
A flattener. What he said is my usual first step and I left that out for simplicity.
But your refractor image may simply be upside down compared to the displayed image.

You can also buy tilt adapters. Teleskop Services sells. Few types ir get Josh to make you one.

Greg
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Old 02-01-2021, 02:23 PM
MarkInSpace (Mark)
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Thanks for your inputs! I found this:
https://astronomy-imaging-camera.com.../new-t2-tilter
I'll order it today!
cheers
Mark
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