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CFF 250mm 10" RC Arrived

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#126 Alterf

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Posted 24 November 2017 - 10:02 AM

Nice, Joel!  This looks like it's working!

 

Best,

 

Val


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#127 akulapanam

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Posted 24 November 2017 - 01:23 PM

SUCCESS!!!

As some of you know from another post, I had a lot of tilt in my system and as far as I could tell it appeared to be a problem in the focuser. Last night was a very clear, steady night with above average seeing conditions.

Here are my collimation/tilt adjusting steps:
1. I squared the focuser flange with the back plate of the scope. The flange was tight up against the back plate.
2. Collimated indoors with the Tak TCS (easy!)
3. Star collimation using the DSI method - a tiny adjustment to the primary and a tiny adjustment to the secondary was needed.
4. At this point the stars across the whole field of view looked great, round to the edges.
5. I took a series of test images on a star field and loaded them into CCDInspector. CCDI showed a large tilt, as expected.
6. I began to adjust the focuser FLANGE to correct the tilt. I realize this is backwards...
7. After making tiny adjustments to the focuser flange, I ended up with a 3% tilt. Not too bad!
I realize that in the above way of doing this, if I rotate the focuser I may introduce a little more tilt, since it is possible that the focuser is not truly aligned with the optical axis. Actually, I removed tilt with the camera angled at 90deg relative to the sky. But I image at 0deg relative to the sky, so I rotated the focuser so the camera was oriented at 0deg and repeated the tilt adjustments on the focuser flange. I was glad to see that rotating the focuser resulted in only a slight increase in tilt, which I then removed by further flange adjustments.
I'm pretty happy right now. I think the system is finally coming together.
Attached are my CCDI results and a single image of NGC891. Here is a link to download the raw fit if anyone wants to take a look:


Looks great! Was this taken without a flattener on the 6200? Also by flange I assume you mean the plate on the back of the scope?

#128 buckeyestargazer

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Posted 24 November 2017 - 01:35 PM

 

Looks great! Was this taken without a flattener on the 6200? Also by flange I assume you mean the plate on the back of the scope?

 

This was taken with the flattener in place with my 16200.  By flange I mean the CFF round part that the feathertouch focuser slides into.  This round part bolts directly onto the back plate of the scope and is adjustable by push/pull screws.  



#129 akulapanam

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Posted 24 November 2017 - 02:20 PM


Looks great! Was this taken without a flattener on the 6200? Also by flange I assume you mean the plate on the back of the scope?

This was taken with the flattener in place with my 16200. By flange I mean the CFF round part that the feathertouch focuser slides into. This round part bolts directly onto the back plate of the scope and is adjustable by push/pull screws.

Interesting. I usually use a laser to adjust that but this clearly worked well.

#130 buckeyestargazer

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Posted 24 November 2017 - 02:35 PM

 

Interesting. I usually use a laser to adjust that but this clearly worked well.

 

That's my whole problem.  I tried that before too.  But when I put the laser in the focuser and aligned the laser dot with the center of the secondary, the problem is that when I would rotate the focuser the laser would trace a small circle rather than stay at a fixed point.  So I adjusted the focuser as best I could with the laser and finished collimation.  But that resulted in severe tilt.

 

This way, by adjusting the laser after star collimation I got rid of the tilt while maintaining collimation.  The only potential problem I see doing it this way is that if I rotate the focuser/camera, then potentially I will introduce a little more tilt because the focuser is not 100% square with the optical center.  In my tests I showed an increase of 2% tilt when I rotated the focuser vs. where I collimated/adjusted for tilt.  



#131 akulapanam

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Posted 24 November 2017 - 07:28 PM


Interesting. I usually use a laser to adjust that but this clearly worked well.

That's my whole problem. I tried that before too. But when I put the laser in the focuser and aligned the laser dot with the center of the secondary, the problem is that when I would rotate the focuser the laser would trace a small circle rather than stay at a fixed point. So I adjusted the focuser as best I could with the laser and finished collimation. But that resulted in severe tilt.

This way, by adjusting the laser after star collimation I got rid of the tilt while maintaining collimation. The only potential problem I see doing it this way is that if I rotate the focuser/camera, then potentially I will introduce a little more tilt because the focuser is not 100% square with the optical center. In my tests I showed an increase of 2% tilt when I rotated the focuser vs. where I collimated/adjusted for tilt.

Hmm I wonder if that cff part is the issue, possibly not cut evenly. If it was then when you rotated the focuser it wouldn’t have a huge impact like you described.


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