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How's my collimation?

collimation reflector
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#1 jetrel

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Posted 07 December 2019 - 07:29 PM

Hi all, telescope noob and first time poster here.

 

Sorry for potato quality. It's taken from my cell through a cheshire. When I began, the black dot (a reflection from the cheshire?) was just outside the paper donut, and I managed to get it inside. I'm still not sure about my secondary - does it look like it needs adjustment?

 

I'm not sure if the focuser should be all the way in or out. It didn't make any difference - the crosshairs on the cheshire were blurry af and were often obscuring the sharp reflection of them either way. Is there a way to combat this, or do I have a crappy cheshire?

 

Thanks

 

 

Edit - doesn't look like upload worked, so here's an imgur link https://imgur.com/a/vC5tgeN


Edited by jetrel, 07 December 2019 - 07:30 PM.


#2 JOEinCO

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Posted 08 December 2019 - 08:15 AM

The image you tried to upload (2600 pixels by 4600 pixels) is FAR too big for uploading to CN. Largest TOTAL files you can upload to a forum is 500KB. You'll need to resize or crop your giant original. 500x500 to 800x800 is plenty big.

 

This is Jetrel's picture: 

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#3 SloMoe

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Posted 08 December 2019 - 08:39 AM

You're close, rotation of the secondary is off, you can see the side to side distance of the center spot, also I only see two of the mirror clips, so try to rotate the secondary a bit to see all three primary mirror clips, then you're close.

 

It's a good thing that the image remains the same no matter where you have the draw tube set.

 

Here are three examples of what you want to see, this part of the learning curve is the hardest because you're learning how to move the mirrors and it can be frustrating, once you'er over this hurdle the next time will be quicker & easier.

 

Also go to Youtube and search telescope collimation and watch as many of the video's as you can stand, it's actually easier to see it done than have it explained in text.

 

Also the cross hairs are confusing you, ignore them, you want to see just the image of the primary mirror on the secondary mirror, clips and all.

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Edited by SloMoe, 08 December 2019 - 08:57 AM.


#4 Vic Menard

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Posted 08 December 2019 - 11:14 AM

I could make a better assessment if you would provide another image with a piece of white copier paper behind the secondary mirror opposite the focuser against the inside wall of the tube--don't cover the primary mirror! as we need to be able to see the primary mirror center marker. I also need to know your scope's numbers--aperture and focal ratio, make and model may also help.

 

From what I could see with the image you provided, I attempted to annotate the image. The blue cross hairs and circle should replicate the cross hairs and bottom edge of your Cheshire sight tube combination tool. The green circle is the best approximation I could make to show where the actual edge of your secondary mirror is currently located. The red circle represents the primary mirror reflection (the primary mirror clip at 7:00 is clipped by the secondary mirror). The red cross hairs may indicate that your primary mirror center marker is slightly displaced--I'll be able to make a better call with a better image clearly showing the actual edge of the secondary mirror. 

 

I think your alignment is already pretty close...

 

(Edit: And welcome to the Cloudy Nights forums!)

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Edited by Vic Menard, 08 December 2019 - 01:10 PM.


#5 Vic Menard

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Posted 08 December 2019 - 01:32 PM

...Here are three examples of what you want to see, this part of the learning curve is the hardest because...

It's hardest because some of these examples just won't go away.  confused1.gif

 

The first example is impossible except for a very long focal ratio scope (which would probably have a smaller secondary mirror)--probably around f/10 or f/12. When the bottom edge of the focuser, the actual edge of the secondary mirror, and the reflected edge of the primary mirror are all centered and concentric, the secondary mirror placement is offset, which means the dark silhouette reflection of the secondary mirror surrounding the reflection of the bottom of the focuser can not be concentric.  

 

The second example/image appears to have been manipulated. I've annotated the image showing that the primary mirror center spot is shifted to the left (I'm guessing to shift the secondary mirror reflection to a more centered position). 

 

The final example is Jason Khadder's illustration of an offset secondary mirror placement for a fairly fast primary mirror (I'm guessing a bit less than f/4). It shows why you shouldn't use the spider to "center" the alignment, and it also shows that while the secondary mirror reflection is pushed off center to the right, it's still round (not egg-shaped)

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#6 jetrel

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Posted 09 December 2019 - 06:42 PM

Thanks for the help everyone! 




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