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Old 02-04-2020, 11:47 AM
Saturn488
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Auto focus issue or mount tracking issue?

I was out the other night taking some nice shots of NGC 5128 and was having a few minor issues getting my target into focus.

Equipment/Software
- HEQ5 Pro
- ES102 APO with ZWO EAF (pretty much this setup file:///D:/Installation%20of%20the%20ZWO%20EAF %20on%20an%20Explore%20Scientific%2 0ED102%20(1).pdf)
- Sequence Generator Pro

I am unsure if I am having a focusing issue or an issue with my mount tracking. Guiding looked to be fine so I can rule that possibility out. I had a look at the focuser today and notice a little bit of backlash but usually between shots I will get one that is really clear and sharp and the next one a tad blurry.

After a bit of tinkering I got a feeling it's my tracking on the mount as I had similar results a while back with another telescope and camera I used with no electronic focuser.

I have attached three consecutive photos of my target. You can see its sharp and in focus, then out of focus then back to normal.

Any ideas on what else I can test especially if I am having a tracking issue with the mount?

Any help would be appreciated!
Attached Thumbnails
Click for full-size image (5.JPG)
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Click for full-size image (6.JPG)
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Click for full-size image (7.JPG)
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  #2  
Old 02-04-2020, 12:34 PM
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bojan
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Yes, third shot is the best. but focus is not changing like this... if it is temperature issue, it would go in one direction only, not back and forth

It could be seeing... jet streams?
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  #3  
Old 02-04-2020, 12:49 PM
Startrek (Martin)
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Chrys
Had a similar issue ( not quite the same ) 2 weeks ago with the same target NGC 5128 ( read my post in Beginners Astrophotography ) Had to refocus just over halfway through my subs ( only because I noticed it , if I hadn’t checked all my subs would have been slightly out of focus )
I put my problem down to the focus drifting caused by atmospheric diffraction / dispersion and Jetstream as the object ascends from lower altitudes ( 30 degrees ) up to higher altitudes ( 70 degrees ) ?
Doesn’t happen that often
Martin
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Old 02-04-2020, 02:16 PM
Saturn488
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I attempted to do an auto focus through SGP but I could never get the U shaped curve and kept failing.
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Old 02-04-2020, 02:31 PM
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multiweb (Marc)
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Quote:
Originally Posted by Saturn488 View Post
I attempted to do an auto focus through SGP but I could never get the U shaped curve and kept failing.
This happens when the seeing is bad.

Your last shot is sharp. I reckon you had guiding issues.
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Old 02-04-2020, 04:11 PM
Saturn488
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Thanks for the replies!

I am hoping it isn't a tracking issue with my mount.

Guiding, come to think of it I did use the same guidescope and camera on my old setup so it might be that as well.

Would there be any tests I can do to verify anything?
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