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First attempt at collminating

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#1 Millerb

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Posted 02 March 2021 - 04:42 PM

Here is my first attempt to collminate my Skywatcher 8" classic dob. Thoughts? I used the Farpoint laser and a cheshire.

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#2 Jim Waters

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Posted 02 March 2021 - 05:08 PM

It looks like you are real close.

 

FYI

http://www.astro-bab...nian-reflector/



#3 MellonLake

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Posted 03 March 2021 - 12:45 PM

Looks good.   Any error between the circles below is likely parallax due to the the camera not being perfectly centred.   Nice job. 

 

Collimation low-small.png   

 



#4 SteveG

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Posted 03 March 2021 - 12:56 PM

Looks good.   Any error between the circles below is likely parallax due to the the camera not being perfectly centred.   Nice job. 

 

attachicon.gifCollimation low-small.png  

I’m a little curious as to why the left side of the Cheshire reflecting ring is cropped. Also, that Cheshire should really be used with the calibrated triangle center spot.



#5 MellonLake

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Posted 03 March 2021 - 02:30 PM

Is the outer circle in my annotated image the side of the drawtube or is it the peep hole in the Cheshire?

The cropped Cheshire is weird. I just chalked it up to Paralax.

#6 Vic Menard

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Posted 03 March 2021 - 03:14 PM

It looks to me like your secondary mirror has a small tilt/rotation error. BUT I don't understand why you have a secondary mirror tilt error if you corrected it with a FarPoint laser. My other concern is the "squaring" of the focuser relative to the tube assembly--but that might be more illusory. The green circle in the annotated image (below) is slightly elliptical (matched to the actual edge of the secondary mirror) and positioned to show the optimal secondary mirror placement relative to the bottom edge of the focuser drawtube.

 

All things considered, even with these errors, your axial alignments are within tolerance and your secondary mirror placement is OK--so you can certainly use your current collimation "as is" and expect good image performance.

 

 

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#7 Vic Menard

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Posted 03 March 2021 - 03:19 PM

Is the outer circle in my annotated image the side of the drawtube or is it the peep hole in the Cheshire?
The cropped Cheshire is weird. I just chalked it up to Paralax.

The outermost circle is the bottom edge of the focuser drawtube.

The cropped Cheshire is partly a secondary mirror tilt error, and partly a secondary mirror tilt/rotation error. It looks worse than it is because the apparent size of the outer edge of the bright Cheshire ring is close to the apparent size of the secondary mirror, which accentuates the error(s).


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#8 Millerb

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Posted 03 March 2021 - 03:48 PM

Thank you all for the input. I will place the triangle center spot on the primary and see what I need to tweak from there.

#9 Vic Menard

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Posted 03 March 2021 - 04:36 PM

Thank you all for the input. I will place the triangle center spot on the primary and see what I need to tweak from there.

For the record, you don't need to tweak anything if you would just rather observe. And as long as you can see your primary mirror center marker/donut in the dark center of the Cheshire, and your laser dot in the center of the primary mirror center marker/donut, you should be fine. Just remember to do the laser first, and the Cheshire last (primary mirror alignment should ALWAYS be last).



#10 SteveG

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Posted 03 March 2021 - 10:36 PM

Thank you all for the input. I will place the triangle center spot on the primary and see what I need to tweak from there.

You should hold off per Vic's advice. He see's things that I always miss!



#11 Millerb

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Posted 04 March 2021 - 08:23 AM

Got to do some observing last night, still lots to learn about finding specific targets. But I got to see Orions Nebula, Mars, the Pleiades, and the blinding Sirius. Mars was small and hard to focus on. Overall very good time last night.
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