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Old 03-10-2012, 05:08 PM
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whzzz28 (Nathan)
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Out of collimation or?

Finally got a chance to play with my VC200L the other night.
From what i was hearing, and reading, the scope comes pre-collimated by Vixen, so it should be pretty good to go straight out of the box.

Well it wasn't.
Threw it up and did a quick polar alignment and then tried to focus.
I was getting what looked like double stars - both of which were elongated; at 0.5s exposures.

Im guessing it was a collimation issue so i threw my laser collimator in to see if the secondary was aligned. It wasn't. The laser beam came back off-center.

I followed Vixen's instructions on collimating the scope - had to peel the Vixen sticker off the secondary to adjust it, but finally got the laser centered. Then i did a star test. Out of focus i checked to make sure it was centered. It probably isnt perfect but it should of been pretty close.
So i threw the camera back on and slewed to two random galaxies to try (M77 and NGC1097 - both are bright). Did 10min shots in lum of each galaxy and the results are terrible. Focus wasn't perfect but should have been pretty good (according to the FWHM i was getting).
See attached.

For 10min subs, there sure is a lack of data. These are stretched very far.
The 'drift' i thought was poor polar alignment, so i went back and checked, but the mount was aligned pretty well and these eggs appear even after only a 1-5sec exposure.

There are two things i can think of that are causing this:
Collimation. Maybe i made things worse? the central obstruction on an out of focus star test is pretty close to the center (checked slightly off-axis).

Improper back focus. I was doing these tests without the reducer, so native @ f/9.
I was not entirely sure at the time of what back focus was required and after reading what others were using, decided to use a 50mm extension tube. After some more reading today i found that the back focus is ~143mm without reducer. So my QHY9 + 50mm was only getting me 100mm or so.
Ive never seen the affects of an improperly placed FF to sensor before so i don't know what it should look like.

Alarmingly i read just before that the secondary is fixed and you only adjust the primary. That might explain the fact that the screws for collimation of the secondary were behind a sticker and were alan screws.

But i think they were wrong and meant that the primary is fixed (as i have also read...).

Thoughts?

Thanks.
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  #2  
Old 03-10-2012, 08:38 PM
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Visionoz (Bill)
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Perhaps a wander through the Yahoogroup for VC200L would help you read up on some of the issues you're facing - I needed only to adjust my secondary because I replaced the spider vanes (with ones that were milled down to very thin) and did not have any issues whatsoever

Also when I did not use the FR (which by the way is pretty good if used correctly) I did not have any problems with focusing on 1)DSLR & 2)CCD imager

These pixs were taken with my kit: With DSLR/no FR and With DSLR/FR and With CCD/no FR

YMMV

HTH
Cheers
Bill
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Old 05-10-2012, 11:48 AM
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whzzz28 (Nathan)
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No ideas?
Other thought was image tilt - possibly focuser related.

Will get back out tonight and try a few things.
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