#21  
Old 29-12-2014, 10:41 AM
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alpal
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Quote:
Originally Posted by raymo View Post
Can anyone help? I have been happily doing subs up to 100-120 secs
with my 8" f/5 Newt for ages. Of recent times I have been aligning using
Sirius and Fomalhaut. All good anywhere in the sky. The last two sessions
I have used different stars [Rigel and Achenar], and my tracking has gone all weird. I got round stars on the Rosette at 60 secs, so thought my tracking was poor, but acceptable for what I was planning for the session, but on the LMC could only get round stars up to 15 secs. Went back to the Rosette and got 60 secs again, but even 60 secs is way short of normal. I have a little out of balance to keep the gears meshed. It didn't
matter how many subs I took; the very poor tracking stayed the same.
I'm not even sure that the poor tracking has anything to do with the alignment process, but I can't think of anything else that has changed.
raymo

I suggest you use an OAG.
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  #22  
Old 29-12-2014, 12:17 PM
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jenchris (Jennifer)
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Would the backlash affect where your apparent point of aim ends up when you're aligning? Would it make any difference?

My Neq 6 seems to be able to stick pretty much to the target with very little adjustment.

Is the ground your pier sits in swelling up with the recent rain?
I've no idea what I'm talking about, just trying to come up with something you maybe haven't included......
Is your puck cracked?
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  #23  
Old 29-12-2014, 02:44 PM
raymo
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The elongation is in R.A. only, and is a practically perfect straight line for as long as I have left it tracking, which is about 7 or 8 minutes, which, as the Dec tracking is as good as ever, shows that my P.A. is as good as
usual. I thought for a moment that I may have had lunar or solar tracking
enabled, but not so. It wouldn't have made that much difference anyway.
I haven't thought to see whether the R.A. tracking is running slow or fast, although I can't see how it could run fast. The really confusing thing
is the huge disparity in tracking quality between targets on opposite sides
of the meridian.
Thanks Jennifer for your suggestions; all comments will be taken on board, as they say.
I would use an OAG alpal, but a thin OAG and guide camera are beyond my budget at the moment, plus L.P. would restrict my exposures to not
much more than the 100-120 secs I normally manage.
raymo
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  #24  
Old 29-12-2014, 03:15 PM
glend (Glen)
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Raymo, Can you explain what you mean by the disparity on different sides of the merdian? If the RA had slop in the gearing it coud explain the difference. Does accuracy improve as you get near the meridian as its climbing or does jt get worse or remain the same. If you did a series of equally timed exposures on a climbing target it might tell you more about how RA is behaving. Reset and then do the same on the falling side of the meridian. I trust you still have RA balanced with more weight on the bar to keep the gears meshed.
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  #25  
Old 29-12-2014, 03:32 PM
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Steffen
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Synscan (in EQ mode) won't track in Dec anyway, you have to have good polar alignment or the stars will wander off in Dec. The fact that your tracking error is in RA only seems to prove that your polar alignment is good.

Will the displacement in RA get continuously larger over time, or does is oscillate back and forth? If it only goes one way (too slow) than a gear slipping on its shaft is a good lead to follow, especially if the RA axis is stiff. The gear on the worm shaft can be tightened with two set screws, but unfortunately the sprocket wheel, once loose, cannot be tightened on the motor shaft. Sounds like your mount could be a good candidate for a belt mod

Cheers
Steffen.
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  #26  
Old 29-12-2014, 03:42 PM
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alpal
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Quote:
Originally Posted by raymo View Post
I would use an OAG alpal, but a thin OAG and guide camera are beyond my budget at the moment, plus L.P. would restrict my exposures to not
much more than the 100-120 secs I normally manage.
raymo

I had the same trouble as you when I started out &
only an OAG can give you guaranteed sub frames - round stars.
Even with my EQ6 correctly drift aligned using the camera
I couldn't go beyond 30 seconds.
Even then - some frames would have to be discarded.
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  #27  
Old 30-12-2014, 11:08 AM
raymo
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Thank you everyone for your responses. I will check the R.A. drive gear to see if there is any slippage on the shaft. If not, I will do some test
subs as Glend suggested, to get a better idea of what is going on.
raymo
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