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Diffraction spikes

Optics Refractor Collimation Equipment
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#1 cancian123

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Posted 20 January 2022 - 09:17 AM

Hi everyone.

I need some help!

 

My refractor telescope started to show  aberrations on bright stars.

This is the image in focus

in focus.png

 

This is the image of the same star a little out of focus.

out of focus.jpg

 

 

I have never seen anything like that.

It is an airspaced doublet.

Does anyone know what could be happening?

 

Thanks a lot!


Edited by cancian123, 20 January 2022 - 09:18 AM.


#2 lee14

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Posted 20 January 2022 - 09:21 AM

The round spots are almost certainly dust. The line could possibly be a hair, on, or between the lens elements. Maybe somewhere else in the optical train. 

 

Lee



#3 lee14

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Posted 20 January 2022 - 09:22 AM

Hopefully not a scratch.

 

Lee



#4 cancian123

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Posted 20 January 2022 - 09:37 AM

I don`t think it is a hair or anything like that. I have already checked the objective.

I also tested two different cameras with and without the flattner, and the abberation is always present, I guesse there is something with the objective.



#5 mikeDnight

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Posted 20 January 2022 - 09:47 AM

There's something in the light path of either the scope or before the scope such as a telegraph wire. Are you using an erecting prism, as the adjoining surfaces can cause artefacts in a star image. 


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#6 PatrickVt

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Posted 20 January 2022 - 10:15 AM

There is something obscuring the optical path to create that thick black line.  This line would also cause a bright object to spike.   Based on how thick this line is, I would guess it is a hair and it is in the area of the focuser tube.  If you are using a prism diagonal, it is possible that it might be the typical prism split but it is off-center due to a slight misalignment of the focuser in relation to the lens cell.  Since this is stated to have just recently developed, my bet is it is a hair somewhere in the optical path back near the focuser.  

 

The circles are likely dust bunnies somewhere in the optical path.  

 

Patrick


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#7 cancian123

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Posted 20 January 2022 - 10:37 AM

I will double check everything today. Thanks guys!



#8 cancian123

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Posted 20 January 2022 - 11:43 AM

Hi Guys.

I think I know what is going on. I just tested my telescope with a very small LED 20 meter away, and it worked as expected, no spikes and aberrations.
Then I realized that this is the first time I use my telescope from my window, and my window has safety bars....

 

window

 

 

I think this is the cause of the problem.


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#9 PatrickVt

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Posted 20 January 2022 - 12:13 PM

Yes, that would be the problem.  Shooting through a window is never a good idea.  The glass in a window is nowhere near close to the quality needed for optical glass, double panes doubles the bad quality plus introduces a double image, and opening the window causes heat plumes.  Of course, bars on the window obstructs the view and causes spikes too.  This would have been good info to have right in the first post!  smile.gif

 

Patrick

 

EDIT:   And, I hope you are released from jail soon so you can get outside to enjoy astronomy!  :)


Edited by PatrickVt, 20 January 2022 - 12:16 PM.

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#10 Jon Isaacs

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Posted 20 January 2022 - 01:18 PM

EDIT:   And, I hope you are released from jail soon so you can get outside to enjoy astronomy!  :)

 

 

:lol:

 

My backyard has a 10 telephone and power wires running above the fence to the east.... I am quite familiar with such spikes.. 

 

Jon


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#11 AndresEsteban

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Posted 20 January 2022 - 09:16 PM

 

Hi Guys.

I think I know what is going on. I just tested my telescope with a very small LED 20 meter away, and it worked as expected, no spikes and aberrations.
Then I realized that this is the first time I use my telescope from my window, and my window has safety bars....

 

 

 

 

I think this is the cause of the problem.

 

I have the same problem, safety bars in my window. They generate diffraction spikes depending on how close to the objetive they are. Some people use safety nets in their windows for their kids, they also produce diffraction spikes although less visible. The best thing is to have nothing at all in between!

Clear skies!
Andy



#12 Tank

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Posted 20 January 2022 - 10:08 PM

That will do it, a branch, telephone line etc will do it glad to here nothing with the optics




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