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Equipment Discussions >> Mounts

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EFT
Vendor - Deep Space Products
*****

Reged: 05/07/07

Loc: Phoenix, AZ
Re: Deciding between two mounts for AP new [Re: orlyandico]
      #5595340 - 12/29/12 11:42 PM

Quote:

I don't see what's the big deal with CG-5 noise.

I don't have a CG-5, but my CGEM sounds like an asthmatic coffee grinder.. and my Mach1 sounds like a muscleman coffee grinder.

In other words, even the Mach1 is pretty darn noisy.




The CG-5 has similar noise to the CGEM since they both use the same motors. However, the plastic motor housings of the CG-5 tend to significantly amplify the noise compared to the CGEM. If you run the CG-5 with the motor covers off, it is similar in sound to the CGEM, although a CGEM can usually be adjusted to be more quiet in the long run.

Interesting about the Mach1. I would have expected that to be pretty quiet.


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Patrick
Postmaster
*****

Reged: 05/16/03

Loc: Franklin, Ohio
Re: Deciding between two mounts for AP new [Re: orlyandico]
      #5595457 - 12/30/12 01:38 AM

Quote:

the only bad news is the sometimes horrific periodic error and the large 8/3 harmonic.




What is the source data for your comments and how many samples have you checked? I'm just wondering since your comments are so negative. Did you have a bad experience with a CGEM mount?

Thanks,

Patrick


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orlyandico
Post Laureate
*****

Reged: 08/10/09

Loc: Singapore
Re: Deciding between two mounts for AP new [Re: Patrick]
      #5595471 - 12/30/12 02:03 AM

hi Patrick,

the 8/3 is quite well known. Even Celestron is aware of it and trying to do a firmware fix (you can check on the - members only - TeamCelestron forum, which is an official Celestron forum). You'll also see regular complaints along this line on the CelestronCGEM yahoo group.

for some CGEM's the 8/3 harmonic is small-ish, but on mine it's huge (about 20"). Mark also has one with large 8/3, and his travails with his CGEM here on CN are well documented.

that said.. the software is great. Like I said, in spite of the huge periodic error, it guides well enough ( < 2" RMS ) which should be good enough for focal lengths under 1000 mm.

I would class it as a "must guide" mount though - on mine the PE is 40" peak-to-peak which makes it almost useless for unguided imaging except very short exposures i.e. 30 seconds, at very short focal lengths, i.e. under 500mm.

There's one guy (Jeff) on the CelestronCGEM yahoo group who images with a CGEM and a C11HD at native focal length. But... he has an adaptive optics unit. My own experience with the CGEM and my C9.25 is that over 1-2 minutes, even with guiding, the CGEM can't produce consistently round stars at f/10. The gear noise is simply too large (and that includes the 8/3). That's 0.68" / pixel though which would be demanding of most mounts.

I think I've been pretty open about my bad experience with the CGEM - but I am by no means alone in this. That said, I am keeping mine, in spite of having two AP's and a couple guys want to buy my CGEM - the software is great, the mount modeling is great, the ASPA is great - it's a great visual mount, if a bit heavy.

But anyone buying one has to be aware of the 8/3, DEC cogging, and large periodic error. Overall I think the Atlas/EQ6 is more trouble-free due to having a simpler gearbox and no known cogging issue.


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orlyandico
Post Laureate
*****

Reged: 08/10/09

Loc: Singapore
Re: Deciding between two mounts for AP new [Re: orlyandico]
      #5595483 - 12/30/12 02:19 AM

one other thing I have to point out - realistically, doing long exposure with any $1500 mount at > 2 meter focal length is going to be a challenge.

a lot of people have great success with CGEM's or Atlas mounts. but if you check they are almost invariably < 1 meter focal length.

when you get to < 1" / pixel things become much tougher and I think it's not fair to expect that sort of performance consistently from a CGEM, Atlas, or comparable mount.

so - CGEM, Atlas, or iEQ45 - all should work fine under 1000mm. But if I was ambitious and going for > 2 meter FL, I think I would choose the Atlas... but I am keeping the CGEM for its sheer convenience and user-friendliness.


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Steve Drapak
member


Reged: 09/18/08

Loc: Toronto, Canada
Re: Deciding between two mounts for AP new [Re: rigel123]
      #5595523 - 12/30/12 03:26 AM

Quote:

Quote:



The Atlas is not quiet so that could rule it out if that is an issue for you. It has never bothered me because I point to a single star to sync (first one is the only one not on my CCD) and then I go inside (the house or my car if somewhere) and remotely connect to my laptop. You'll also find that you only slew once per object so it isn't that big of deal.

Dan




I think that is the first time I have heard anyone say the Atlas is noisy. I have to have my ear right beside my Atlas to even hear it when it slews.

I totally agree that it is a great mount.




My EQ-6 got a bit noisy after a year or so, sounded like a garburator when slewing fast, I tightened up the gear meshing (found a step by step guide using google) and ever since it's been as quiet as anything, just a low whine when it slews.


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andysea
Pooh-Bah
*****

Reged: 09/03/10

Loc: Seattle, WA
Re: Deciding between two mounts for AP new [Re: Steve Drapak]
      #5595532 - 12/30/12 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....


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orlyandico
Post Laureate
*****

Reged: 08/10/09

Loc: Singapore
Re: Deciding between two mounts for AP new [Re: andysea]
      #5595547 - 12/30/12 04:07 AM

Andy - I don't see you upgrading that NJP

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andysea
Pooh-Bah
*****

Reged: 09/03/10

Loc: Seattle, WA
Re: Deciding between two mounts for AP new [Re: orlyandico]
      #5596008 - 12/30/12 12:01 PM

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

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Luke Jones
journeyman


Reged: 03/27/09

Re: Deciding between two mounts for AP new [Re: andysea]
      #5611370 - 01/08/13 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.com/photos/40282801@N07/8010537911/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.


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nomosnow
sage


Reged: 03/21/11

Loc: Fort Saskatchewan,Ab ,Canada
Re: Deciding between two mounts for AP new [Re: Luke Jones]
      #5611972 - 01/08/13 01:40 PM

Luke , keep up the good work 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 .
John


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