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Deciding between two mounts for AP

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#26 andysea


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Posted 30 December 2012 - 03:40 AM

My Mach1 is pretty noisy when it slews full speed. My Njp sounds like a dentist drill. They both track well, I wouldn't worry too much about noise:)
Going back to the op's question I wouldn't agonize over which mount to buy. The reality of this hobby is that there is no lifetime purchase. Whichever mount you end up with chances are you will be upgrading again and again and again....

#27 orlyandico


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Posted 30 December 2012 - 04:07 AM

Andy - I don't see you upgrading that NJP :)

#28 andysea


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Posted 30 December 2012 - 12:01 PM

Lol you have a point there!! I still want ap900 because it looks so cool!

#29 Luke Jones

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Posted 08 January 2013 - 05:03 AM

I've found my IEQ-45 to work very well, other than for periodic error in the geared motor (not the worm). I should mention that I'm very demanding with quality and trying for mount performance far beyond the IEQ-45 price tag. I have an 8" LX200 on the mount and image at the demanding FL of 1800mm-2000mm, which seems to be well beyond typical IEQ-45 use (far as I can determine).

Since working out that there's 3 secs of DEC backlash (slop in the geared motor) I've got outstanding DEC tracking at around 0.5 arcsec.
The RA tracking is much more interesting. The three motors I've tested all exhibit a perfect sinusoidal periodic error of 4-7 arcsec every 6.5 secs. To see this properly you need a high resolution encoder sampling many times a second. This corresponds perfectly to the geared motor's 64:1 ratio. I've built a high resolution RA encoder to autoguide the mount using the fast ST4 interface, but found that at my high focal length coped poorly with motor gear periodic error, leading to stars that are more elliptical than round. This is because a 6.5 sec period is too fast to correct.
Over the last few (cloudy) days I've managed to run wires from the motor encoder to my own RA encoder micro-controller, and add predictive slow down/speed up commands to adjust for motor encoder periodic error. The results look like excellent RA tracking to +/- 1 arcsec (not yet field tested with stars).

This info is long-winded evidence to back up the warning I'm giving you that you could be in for elliptical stars if aiming for maximum quality at high focal lengths. The more rough your polar alignment and DEC tracking is, the less you'll notice RA problems where stars aren't round ;)
Here's an image to explain the periodic error (worm + geared motor) - http://www.flickr.co.../in/photostream

For visual use I find the mount to be awesome, and if you're not too demanding in the areas I described, you should also find it good for AP.

#30 nomosnow


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Posted 08 January 2013 - 01:40 PM

Luke , keep up the good work :jump: and please keep us posted on your results both here and on the iEQ45 yahoo imaging group.
I find that my mount has acceptable tracking for my 750 mm fl reflector.But... I wouldn't push it above that .

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