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AVX Balance issues?

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#1 torsinadoc

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Posted 18 February 2014 - 09:11 AM

The last two sessions I have noticed that the closer I get to zenith the more drift I get. If I take a 15 second duration shot near zenith I will get long star trails. If I drop to the level of the double cluster, this is not an issue. I can guide for 5 minutes at the DC without difficulty. I suspect it is a balance issue with dec? I take my scope with all attachments including camera, balance it on a thin piece of wood and mark it. Then try and center that mark on over the axis. It is impossible to balance it otherwise as the dec is so stiff. Even when trying to PA the mount I have noticed that the star tends to drift a little. I tore it down and made sure everything was level. I plan on realigning it tonight. Thoughts? Before when it was PA I could image for a minute or so without any streaks.

#2 rmollise

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Posted 18 February 2014 - 10:28 AM

I would suspect that RA balance is the problem. It's usually a mistake to try to image objects near the Meridian or, especially, which will cross the Meridian during the exposure. The only answer, really, is, like the doctor said, "Don't do that." ;)

#3 BarrySimon615

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Posted 18 February 2014 - 10:44 AM

If you have the ability to balance your payload another way (as you did using the thin piece of wood), that is about the best you can do. With a good distal/proximal balance point marked (taking into account different eyepieces, camera equipment, etc.), dec. balance should probably not be the problem.

Note - I still maintain that while 2 plus 4 alignment/calibration might be good for finding things, unless the RA axis of your scope is relatively polar aligned well, you will have drift. The mount's innards adjust for that drift in finding things but when you are relying on the scope's RA drive to give you stars that are not streaked over a stretch of time whether it be 15 seconds or 5 minutes and all points in between and you really do not have a good "optical" alignment on the pole, the stars will be streaked. The only way they would not be would be if you would hear the mount "self correcting" it's position with small bursts of dec. or RA correction over the course of your exposures and it does not do that unless you have an auto-guider.

Other considerations: Are your tripod legs tight? Are you setting up on soft ground? Your mount might be suffering with SSS "Slow Sinking Syndrome".

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#4 torsinadoc

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Posted 18 February 2014 - 11:00 AM

Yes on soft damp ground. May go pick up some pavers after work and set up on that. With guided it didnt appear to be an issue after 5 minute exposure (lower). Just something new that has occured (after 1 year of use). Was concerned that it was mechanical and not user error

I havve had no issues with imaging at the meridian before with guide scope. I am going to try and reset it up and re polar align tonight.

Thanks

#5 T1R2

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Posted 18 February 2014 - 04:31 PM

the telescope should be balanced for the area of sky you are pointed, if your scope is on the west side of the mount, their should be a slight imbalance to the CW side, if your scopes on the east side their should be a slight imbalance to the telescope side, so that the worm gear has some load to push against, so you could be more of a perfect balance, that would cause some movement(backlash) in the gear when crossing the meridian. I'd check your balance, it could be very easy to get it slightly wrong for that area of sky.

#6 torsinadoc

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Posted 19 February 2014 - 05:40 AM

I rebalanced The scope and polar aligned again and everything seemed to work fine. I still have to get pavers to keep it from sinking which I'm sure will happen when we get our rain tonight and tomorrow. I leave the mount only outside in a telegizmo 365 cover






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