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what's the PE on the old AP 600E and 800 mounts?

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#1 orlyandico

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Posted 24 October 2011 - 02:51 PM

I'm curious.. how do they compare to say a G11 without the Ovision worm?

neither the 600E nor 800 are upgradeable to GoTo (particularly the 800 with its backlash-free yet primitive tangent arm declination drive) but after using a DSC for a bit.. I'm beginning to like the idea of non-GoTo DSC.

#2 Tom and Beth

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Posted 24 October 2011 - 06:40 PM

FWIW, Howard (AP tech) has stated on numerous occasions that the earlier mounts were not tested for PE. I do have an early 90s version of the 1200 (DA), as well as a 600E GOTO. I don't see a significant difference in tracking errors between them, but bear in mind I'm 100% visual observer.

I can only tell you that these mounts in use just fade into the background, working with minimal issues day and night. The two-three minor problems I had over the years were promptly resolved either over the phone or by email.

I have no direct experience with the Losmandy mounts.

#3 rainycityastro

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Posted 25 October 2011 - 04:23 PM

I own an AP600E mount although it is one of the later versions. I use it for astrophotography and it tracks with an RMS error of about .15 pixels when autoguided with an orion auto guider at about 300mm FL. Not sure if this is the best I can get out of it or what it translates to in terms of PE. One of these days, I will measure the PE with pempro.

However I find the mount completely adequate for my needs. Please see this image:
http://www.flickr.co.../in/photostream
and a 100% view below/comparison with a hubblesite image.

http://www.flickr.co.../in/photostream

#4 orlyandico

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Posted 26 October 2011 - 09:58 AM

Hmm.. RMS error when guiding doesn't really tell me much. Guiding with a DSI Pro and a 420mm FL, I get RMS errors anywhere from 0.33 to 0.60 on my Vixen Great Polaris. Since GP's have periodic error around the +/- 20 arc-second range, does that imply that a 600E is "only" +/- 10 arc-second?

#5 rainycityastro

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Posted 27 October 2011 - 04:11 PM

Are you planning on using the mount unguided?

I would like to think that the 600E is a lot better than +/- 10 arc seconds unguided. But I haven't measured it. I also haven't even tried optimizing Phd for my setup and have simply left everything at default. However I am getting round stars at about 1.1 arc sec/pixel. Clear nights are very few and far between (I live in one of the cloudiest regions of the US) and I am usually imaging on any clear night that I manage to get out.
The G-11 with the ovision worm might be comparable to AP mounts in periodic error but several people have reported that the moment to moment error can be much higher and fast changing. This is due to errors in the entire gear train outside of the gear train(motors, spur gears, etc.)
AP and similar high end mounts have smooth moment to moment errors so what error exists can be easily autoguided out.

#6 orlyandico

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Posted 28 October 2011 - 12:31 AM

rainycity,

no am not considering unguided.

what sort of payload and exposure length are you pulling on your 600E with round stars? I assume you are using the Q with the Canon DSLR? so that's about 600mm range and 15lb or so?

#7 rainycityastro

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Posted 28 October 2011 - 01:45 AM

Hi Orlyandico,
I think my payload is around 25lbs (scope/rings/camera/guidescope/second camera/wide angle lens piggyback). I need 18lbs of counter weights to balance this out. I have imaged with the FSQ and the 1.6 extender (around 850mm FL) with perfectly round stars. 10 min subs are no problem with this setup.
I found something interesting though: I noticed that dew heater cords hanging from the scope created pretty bad guiding errors. When I tidied it up, the guiding improved significantly. :) You may not have such a bad dew problem where you live.

#8 orlyandico

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Posted 28 October 2011 - 02:05 AM

hm. interestingly, i got guiding errors with the USB cable from my guide camera getting pulled..

#9 orlyandico

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Posted 25 November 2011 - 06:46 PM

Got the early silver 600E QMD on a-mart, 7.8 arc-seconds P-P before PEM.

Got me thinking though, for the same price I could've gotten a new non-GoTo G11, which carries far more weight.

Oh heck..!

#10 rainycityastro

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Posted 26 November 2011 - 02:23 PM

AP does command a premium price due to its premium construction (and brand). I was fortunate however to get my 600e gto for about the same price as a non gto g11.
The AP has periodic error but it is very smooth and can be easily guided out. I would not worry too much about the magnitude of the error itself unless you are not autoguiding.

#11 orlyandico

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Posted 26 November 2012 - 10:24 AM

Hi Ram,

resurrecting this one-year old thread.

You mentioned 0.15 pixel RMS at 300mm FL with the SSAG. That combination is about 4" per pixel, so your RMS guiding error is 0.6"

My copy does about 0.11 pixels at 9.71" pixel scale (176mm focal length, Meade DSI) so about 1.07". My AP600 was non-GTO though and after I converted it to GoTo I think the residual guiding errors are due to gear noise.

My copy is also about +/- 4" unguided, so you were right that they are much better than +/- 10".

However I've been told the Mach1 can give 0.1" RMS guiding? have you measured yours? that is much cleaner than the 600. About 5X to 10X in fact...

#12 andysea

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Posted 29 November 2012 - 02:29 AM

Hi Orlando. I've only used my Mach1 twice but I can tell you that I was getting an RMS about 0.3". I suppose I could improve that by tweaking my guiding parameters which I didn't change from the ones I use with my NJP.
0.1" might be possible on nights with perfect seeing.

Andy

#13 orlyandico

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Posted 29 November 2012 - 03:29 AM

hi Andy,

yup still here. still vacillating over the NJP vs Mach1 vs keeping the money in my pocket.

frankly if I can get even 0.5" RMS i would be happy. Ram says he can do 20 minute subs guided with his 600 at 1600mm with the AT8RC - if I could do that, consistently, I'd be ecstatic and I wouldn't be on the market for another mount.

my problem right now is declination guiding (subject of my other thread). One last try... teflon washers on the DEC thrust plane bearing, and anti-stiction gear lube on the bronze bushings. that's it. if I can't get the declination to behave, it'll be time to pay AP...

oh and the funny thing about my gear noise... my 600QMD GoTo conversion uses the exact same stepper motors used on the NJP. They are Vexta PK245 spur gear steppers. But the NJP doesn't have gear noise problems... I think the encoder on the worm itself allows to have a tight feedback loop to correct for the periodic error of the spur gearbox.

#14 andysea

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Posted 29 November 2012 - 09:04 AM

I can vouch for Ram's claim as I have seen it when imaging together.
I'm not sure what the gear noise that you are referring to is. I am no expert when it comes to stepper motor mechanics but I remember reading that the controller has a lot to do with their precision too...but you probably know all that. As far as I know the TAK does not use the encoder to correct for PE as I don't think they use high resolution encoders.
Regariding the 600, I think AP made a lot of improvements to their 600 during the production years and a late model one might have much better performance than an older one.
Andy

#15 t.r.

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Posted 29 November 2012 - 12:58 PM

I recall reading +8/-8...but I have no idea where or even if it is correct...

#16 andysea

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Posted 29 November 2012 - 01:41 PM

hi Andy,

yup still here. still vacillating over the NJP vs Mach1 vs keeping the money in my pocket.


Just get both!!....j/k :)

Andy

#17 rainycityastro

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Posted 29 November 2012 - 06:25 PM

Orly, not sure if you saw this site:
http://www.astrosurf...nt/ap600gto.htm

This owner gets around 6 arc secs P-P PE on his AP600 but with some strange randomness in his PE. That is firmly in Mach1 territory.
I haven't measured mine. Clear skies are so rare around here that they are strictly reserved for imaging!

Seeing in Singapore is probably world class (equatorial island climate with no turbulence) so for you 0.1" RMS is quite achievable if you got a mach1.

#18 orlyandico

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Posted 29 November 2012 - 07:21 PM

mine is a lot cleaner than that..
Posted Image

and smoothed with only the fundamental..
Posted Image

so about +/- 5". PEMPro has a different way of measuring things and reports about +/- 4".

but i reiterate - my problem is not periodic error, it's declination guiding. I found on some CNC forum that an anti-stiction gear oil made for limited-slip differentials helps these things, so i ordered a quart :tonofbricks: will take 2-3 weeks for me to get it.

#19 andysea

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Posted 29 November 2012 - 07:47 PM

Orlando
Can you please point me to your other thread about dec guiding? I am quite curious now.
Thanks
Andy

#20 orlyandico

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Posted 29 November 2012 - 08:30 PM

oh its basically massive stiction in DEC.

Pics here -
http://www.cloudynig...5543275/page...

cross-posted here -
http://www.cloudynig...5543605/page...

this causes the DEC to "jump" when guiding. Even if I only guide in one direction.

i put some teflon washers under the thrust bearing and that helped when the scope not pointed straight up. but when it is, the load is carried by the DEC bushing (and note, the AP600E GTO like Ram's uses the exact same bushing).

like i said... if i can get rid of the DEC guiding issue, i "should" not "need" a Mach1 anymore, hahaha!

BTW i know another AP600QMD user who also has major challenges with sticky DEC. But he's using an FSQ106 (like Ram!) and with that FL, and good-enough polar alignment, DEC guiding isn't a major issue.

To be honest, when I'm using my Orion 100ED, I can live with the DEC guiding issue. I can do 20-minute subs without issues. But when I have the C9.25 on there.... that's when the DEC stiction becomes an issue. Both because the much heavier load produces greater stiction, and the very long focal length.

#21 andysea

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Posted 29 November 2012 - 10:39 PM

Thanks Orlando. The NJP has conical bearings which probably work better than the ones in the 600.
Have you tried replacing the bearings? I know that with Tak mounts the bearings are easy to replace and they are inexpensive.

#22 orlyandico

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Posted 29 November 2012 - 11:04 PM

I would if I could.. but the 600 doesn't use bearings (it uses brass bushings)... that said the tolerances on those bushings is very high - like I mentioned in the other thread I tried to wrap 0.025mm (1 mil) PTFE film around the declination axis, and it would bind. So the tolerance is < 0.001"

I suspect this is the same design as the 900QMD - which is why AP actually has a "900QMD declination upgrade" program which gives the 900QMD the declination axis of the 900GTO.

#23 andysea

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Posted 29 November 2012 - 11:17 PM

duh that completely went over my head. I understand now.
That's not a very good design is it? I don't see how having two meal parts against each other would provide smooth motion.
I suppose the bushing is the softer metal while the shaft is the hard metal. Given the extremely tight fitting of those parts, as soon as the lubricant wears out, the soft metal probably wears out too and My guess is that your stiction problem is caused by the parts having a minuscule amount of play. Once the load is off to the side that will cause the shaft to bind. Correct? Are the bushings proprietary design? not replaceable?

#24 orlyandico

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Posted 29 November 2012 - 11:22 PM

I took apart a Vixen GP and it also had bushings.

I would not consider this to be "bad design" - Ed Thomas can probably weigh in here but well-made bushings would probably outperform poorly-made bearings (like those in the China mounts).

This is also why you've got a lot of folks replacing the bearings in their China mounts with Timken or SKF bearings.

I had thought about replacing the main declination bushing with a large bearing - but it would require massive machining and destroy the value of the AP600 as an antique / collectible.

There used to be a long waiting list on AP600's - I can imagine Wally toiling at the mill / lathe making each of these by hand without benefit of CNC :D :D :D

#25 andysea

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Posted 30 November 2012 - 12:15 AM

True. I would not venture into a re-machining project. Yes Ed would probably have a better insight into the design. Could the bushing have worn out unevenly? Maybe the mount was used at the very limit of it's payload for a long time. Every time you have the scope pointing up, that would have put an uneven load onto the bearing surface of the bushing. I assume that the bushing, once in place does not rotate which means that the same portion of the bearing surface is always subject to the same load each time the mount is in a certain position.
Was the mount in a permanent setup? Ram mentioned to me an old thread where the owner of an NJP had the mount in a permanent setup for the longest time. That caused the gears to wear unevenly which eventually started to show up in their imaging sessions. DIfferent issue but somewhat possibly related.






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