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Tracking accuracy - ranking

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#1 A. Viegas

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Posted 18 September 2012 - 10:54 AM

I was thinking about future mount/scope upgrades and was wondering what is the tracking accuracy of most of the major mounts, both without autoguiding and with guiding. If we were to rank them, how would they stack-up?

So if we could fill in a table like this:

Mount.......................Unguided.......Guided
CG5-ASGT....................90-120Secs.....?10 mins? dunno?
CPC on wedge..................? ...............?
CGEM..........................? ...............?
CGE
LX80
etc...

I have not yet gotten into autoguiding but am thinking about it. I doubt I need much more than 2-5 mins at this time in any event for my particular setup... but at some point in the future I hope to seriously upgrade and do some more detailed work... of course that is many years away, so this is mostly just a request for education...

Al

#2 Jared

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Posted 18 September 2012 - 11:00 AM

I don't think you can list times for this--depending on the weight and focal length of the scope involved and how careful the polar alignment was you will get dramatically different results. Your best bet is probably PTV error in arcseconds.

I'm also worried that the variability in a given model--especially non-premium models--would keep this list from being very useful. Would you measure performance as shipped? After replacing grease and adjusting gear mesh? After sending the mount out for a hyper-tune?

#3 astroRoy

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Posted 18 September 2012 - 11:08 AM

Maybe one could use a list of this sort if "reasonable expectations" were factored in and for given criteria. Something like "out of the box with 75% rated payload". Maybe even group the mounts to similar payload capacity. Of course it would be subjective and how many people have actual experience with more than a few mounts of a group, let alone more than one group. I would think there are enough people here that have read enough reviews and reports and complaints and kudos, that a "reasonable expectation" list could be produced by consensus.

Roy

#4 Footbag

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Posted 18 September 2012 - 11:12 AM

I've always used this site for a general overview of mount performance.

http://lambermont.dy...g/astro/pe.html

#5 Stew57

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Posted 18 September 2012 - 11:30 AM

Jared is right the variability of a given mount is too great. You could get each user's data but it would not transfer to a meaningful data set.

For example my first CGEM had really bad pe. Most 20 second shots had bad star trails with the c11 at F5. But when the worm was at the point of of cganging direction of the pe curve you could get a 30 second shot with no star trails. Of course the same thing happens with my last cgem. I can get a 112 second unguided shot with no trails but only about a third of the time. Again it deoends on where in the wiorm cycle the shot is taken. That is only one variable.

#6 dickbill

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Posted 18 September 2012 - 12:23 PM

Let's assume people input their best shots, who wants to know the performance of a lemon?.
But you absolutely have to mention the focal lenght otherwise it's meaningless. I suggest we input the values around 1 meter focal lenght, lets say in a range between 750-1300mm, because those numbers are relatively common.
Sure, a C14 can image at 4 meters, but there is no C14 on a cg5.

#7 freestar8n

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Posted 18 September 2012 - 12:29 PM

If you are interested in non-guided performance, then you should look at how well the mounts do with PEC applied - and how hard they are to polar align.

If you are interested in guiding, then you should look at how well other people have done when guiding the mounts by the approach you might use. If you have a refractor guided by a small guidescope - then all of them may do ok. If you are guiding a big sct with off-axis guiding - then there would be more challenges. But it's hard to go by simple metrics to tell how well a mount will do when guided - since it depends a lot on technique and what ota you are guiding in the first place. And if you are unguided, you should fold in how well PEC works on a given mount.

The other concern is the issue of yield - when unguided. You may be able to do 2m unguided images that are acceptable, but you throw away every third image. That means you have to image longer to get a good result - but as long as you have enough good frames to work with, the image will be ok.

Frank

#8 Alph

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Posted 18 September 2012 - 01:20 PM

Again it deoends on where in the wiorm cycle the shot is taken. That is only one variable.


I also depends on
- The worm gear position w.r.t. the worm.
- How the clutches were tightened.
- Variability in balance

My take is that none of the mentioned mounts produces consistent results. Your best bet would be the CGE though.

#9 A. Viegas

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Posted 18 September 2012 - 09:24 PM

Adam, that is a great website... wow! i never imagined there were so many mounts!

yeah, i suppose i asked a very open ended question here... my general request was really to just get a range of experiences, of course making true comparisons may be less meaningful...

Al






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