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Do direct drive mounts really not require guiding?

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#26 GIR

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Posted 05 March 2013 - 02:53 AM

Have to agree with Waldemar, ASA is simply an astonishing mount ...very fast, unbelievably accurate and silent. The only noise comes from the camera fans. I used to have G11 before and you can't really compare those two mounts.

Making a pointing model is easy and fast, especially if you plate solve using bin 3x3 to speed up the download time. Building a very accurate 50 point model takes about 15-20 minutes, depending on what kind of camera and computer you have.A 10 point MLPT takes couple of minutes.

However, you can actually use an old model even in the field because there is a special feature just to adjust the polar alignment with 3 points. Haven't tested it myself yet because I have a permanent set up. Anyway, you don't necessarily need a large pointing model if you're using the MLPT feature; 20 points should more than enough.

Making the ASA mount work properly requires some tuning, however most of it is very simple to do and has to be done only once.

ASA DDM60 Pro

#27 psandelle

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Posted 05 March 2013 - 01:16 PM

Quick question to the ASA mount guys & girls - after really looking it over, I think the term "unguided" is a bit misleading, in that the ASA software, in a way, does predictive guiding based upon real pics taken by the CCD and mount (plate solves, errors accounted for, etc.) - but it internally checks where it should be against the encoders, where a guidescope/OAG CCD setup checks against the external value of the star displacement. So, it is kinda "guided" - just in a different manner (it's not like you point the mount at an object and let 'er run and it somehow "magically" stays on the target - it solves and predicts where to be).

Anyway, that being the case, have any of you figured which was more accurate, an external/OAG guided ASA mount versus the ASA software's "internal" method of guiding? I mean, both methods have error, I would think. If there were some numbers that said that the ASA software/plate solving method was more accurate than a guider, that'd be interesting. And, yes, I understand people are getting 20+ minute "unguided" subs on the ASA's, but was curious if those 20+ subs were better or worse, analytically, than the same mount/scope with a guidescope/OAG.

Thanks, just curious,

Paul

#28 elbee

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Posted 05 March 2013 - 01:30 PM

for those of you that have/use an ASA mount i have a question. i have seen MLPT work, and it works extremely well without guiding (10-15min subs and modest FL), BUT from what i have observed, the MLPT model can not handle a meridian flip. you build the MLPT model either before or after the meridian flip. so how do you run an automated session (i.e., ccdautopilot, acp, etc) without having to be there to rebuild an MLPT model following a meridian flip?

EDIT: one other "problem" i have seen with MLPT within an automated session. the MLPT model will not easily account for time taken out to do refocus runs. MLPT seems to rely very heavily on knowing where the object is in the sky within a time interval t(start) to t(finish). if it is not where it is supposed to be (because some time was taken to do a temperature dependent - unexpected - focus run), things don't go so smoothly.

thanks

#29 blueman

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Posted 05 March 2013 - 01:31 PM

Guiding is not difficult and it is not that expensive either. If you are imaging, well you have everything but the guide camera and scope anyway. Most acquistion software will guide, so there is not that much extra effort to guide in my opinion.
Blueman

#30 psandelle

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Posted 05 March 2013 - 01:37 PM

blueman - I don't think guiding's tough, either (or expensive, or whatever people say), but in looking closer, I realized that the ASA software is doing something akin to guiding anyway, but I don't know how accurate compared to "external" guiding methods. Was curious.

Also, if you're using the ASA method, would external guiding be superfluous if the ASA method were more accurate.

Paul

#31 SL63 AMG

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Posted 05 March 2013 - 02:24 PM

Being the owner of a DDM85, I will agree with everything said by the other owners of ASA DDM mounts.

I first owned a DDM60 prior to them putting fixed encoders on each axis and I didn't like the setup. I still don't like the tip tilt system of the base plate for polar adjustments.

The DDM85 offers a much better method where the base plate rotates for RA and the DEC axis is lifted by a hand wheel.

That being said, setting up the DDM85 for portable use isn't an issue. I set mine up in my driveway every month. I used a sharpie to mark the positions of the tripod feet and this gets my polar alignment to within a few arc minutes each setup.

I could image 5-10 minute subs easily with a polar misalginent under 5 arc minutes, but I am rather anal and won't accept anything less than 0.5' of error and I almost always achieve 0.3' (<= 18") or better.

In order to get this accurte of polar aligment usually requries me to shoot 3 autopoint files of 10-15 stars on one side of the mount, then go find a star on the southern meridian near my latitude, center it on my CCD chip, instruct Autoslew to make a polar correction and then manually dial the star back onto the center of the chip.

This used to take some time with my QSI583wsg because the camera download time is slow, but with my FLI ML8300 combined with connecting my mount to MAxim for telescope control, I can knock out polar adjustment in about 10 minutes, so chalk up about 30-40 minutes for a very accurate polar alignment.

Once my polar alignment is complete, I make a 50 star pointing model with 25 stars on each side of the mount. This takes about 15 minutes. The accurate pointing model corrects all left over polar alignment error, collimation error, mount angle error offset constant and applies a fourrier correction. About the only thing no corrected for is Hysterisis, which all telescope systems exhibit to some degree or another.

Once corrected, I go to my object, synch my plate solving program Sequence (also used for polar alignment and pointing model) and then I start MLPT.

MLPT is a unique tool. Basically, you tell it how long is your total exposure time for all subs, how long each sub is and then tell it to go. It shoots a sub at each point along the arc of the object and plate solves the image, then calculates where it is in the sky versus where it should be in the sky. MLPT then makes corrections during the entire image run keeping the system on track, corecting for all of the items I listed above.

I have discovered through much trial and error that it is best to keep your points small. In other words, if I am shooting 10 minutes subs for 100 minutes, instead of telling that to MLPT, I get better results telling it to run MLPT ar 100 minutes for 5 minutes usbs forcing it to shoot 20 points along the arc.

Anyway, it works as advertised. I have taken up to 30 minute unguided subs at 900mm FL F/3.6 and up to 15 minute subs at 2432mm FL at F/8.

As elbee stated, there are some drawbacks and I am now trying to leanr how to guide the mount for long narrowband exposures at 2432mm FL.

Two of the disadvantages of MLPT are that you cannot leave the MLPT run to go autofocus, such as during a temperature change, and you cannot image to the meridian, flip, then start again without executing another MLPT routine, which is a user intervened process.

The mount can be commanded for automatic meridian flips, but then you lose MLPT.

This is anothe reason I see autoguiding useful for long exposures.

A benefit of the ASA mount for autoguiding is the fact there is no periodic error and there is no backlash.

The optical encoders on the DDM85 are accurate to .02" which is quite incredible.

I could go on and on about the mount, but suffice it to say it is accurate, it does work as advertised and I wouldn't trade mine for any other mount. I might one day get another mount, like an AP or Paramount, mostly to learn something new, but I would not give up my ASA ot get one of these even with the MLPT issue.

I believe Dr. Keller will one day script MLPT so that it can be controlled by ACP and CCDAutoPilot. There is no reason not to as it takes only a few parameters.

Once MLPT can be scripted, one can script an MLPT run for any lenght of time, interrupt it, go focus, do a meridian flip, whatever, then come back and initial another MLPT and start imaging again.

By the way, the time it takes to do MLPT varies based upon the length of your total exposure time, number of exposures and the length of your plate solve exposure.

For most of my MLPT runs, setup is 5-8 minutes. Once can also increase the MLPT iterations for better accuracy, such as when shooting low in the southern sky.

I have to go take my friend to the airport. I may write more later if I can think of anything worth posting.



My physical setup time is about two hours, which I do during the day.

#32 psandelle

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Posted 05 March 2013 - 03:26 PM

Dave - great summation about everything. I now have a much better understanding of how it all fits together (MLPT, guiding, etc.). Very cool. As I move forward over the years, I'll keep this in mind on picking my next mount.

Paul

#33 Per Frejvall

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Posted 08 March 2013 - 01:53 AM

I've test shot a 1-hour sub at M106 with a 190MN mounted on my 10Micron GM2000HPS - unguided. The mount keeps the pointing model in-mount, so once you have a model you actually don't need the PC per se.

I recently added a GM1000HPS as the GM2000HPS is going away to a remote site in Southern France, and that little bugger looks very promising.

If unguided is your aim, 10Micron mounts may be a good choice.

/per

#34 jjongmans

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Posted 08 March 2013 - 03:30 AM

I'm using an ASA DDM60 in a permanent setup. The performance is outstanding. I could achieve 30 min. unguided subs on the first night using it. I ran an automated three-star-polar-alignment-pointing-model, did an accurate polar alignment. I don't use MLPT, but I use an all-sky model with 50 points, also automatically created. After that I could take 30 min. subs with a focal length of 2000mm.

#35 TerraPassenger

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Posted 10 January 2014 - 09:09 AM

I'm thinking about purchasing a ASA DDM60 Pro. However, I will need to use this mount in a portable configuration - setting it up and then tearing it down each night.

I'm wondering, how long does it take to set up the ASA DDM60 Pro in the field? Assume that the setup location is new - one that you've never visited before.

I'm interested in the DDM60 Pro but based on what I've read, field setup may be quite a bit longer than for other mounts.

Thanks in advance for your help.

Dave

#36 Waldemar

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Posted 10 January 2014 - 03:32 PM

did you not read this thread?

#37 rmollise

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Posted 10 January 2014 - 04:25 PM

Any mount that doesn't require guiding is going to require you to build up a pointing model.


Not really. a pointing model might or might not be required, but it has nothing to do with the mount's lack of periodic error or drive system. It has to do with the go-to alignment system used. ;)

#38 TerraPassenger

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Posted 10 January 2014 - 05:39 PM

>> did you not read this thread?
Yes, I did.

For the user who pre-marked his DDM85 location on his driveway it sounded like 30-40 minutes for polar alignment, followed by 15 min for a 50 star point model followed by 5-8 min (times 2? if a meridian flip is needed) for a MLPT which is 30+15+2*10=65 min.

The reason I've restated the question is to confirm the above estimate.

#39 jrcrilly

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Posted 10 January 2014 - 06:19 PM

Any mount that doesn't require guiding is going to require you to build up a pointing model.


Not really. a pointing model might or might not be required, but it has nothing to do with the mount's lack of periodic error or drive system. It has to do with the go-to alignment system used. ;)


For unguided imaging at most focal lengths a pointing model will, indeed, be required to compensate for things like declination drift, flexure, and atmospheric refraction. Without a closed loop from a guider, those can only be derived from a model.

#40 rmollise

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Posted 10 January 2014 - 09:26 PM

A pointing model won't do a thing for declination drift. A T-point assisted polar alignment will. The go-to alignment doesn't do squat for tracking.

#41 Odell

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Posted 10 January 2014 - 09:32 PM

Or:

http://www.siderealtechnology.com/

#42 frolinmod

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Posted 10 January 2014 - 10:02 PM

The go-to alignment doesn't do squat for tracking.

It makes a big difference here with my EdgeHD 14 and Paramount ME with ProTrack enabled and active. So much so that I would never want to image without it.

#43 jrcrilly

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Posted 10 January 2014 - 10:17 PM

The go-to alignment doesn't do squat for tracking.

It makes a big difference here with my EdgeHD 14 and Paramount ME with ProTrack enabled and active. So much so that I would never want to image without it.


ProTrack was probably the first such solution offered to the amateur market. A number of other high-end manufacturers have since implemented such systems. Sounds like a great idea to me! ;)

Earlier implementations of auto dec corrections (Meade's dec drift training and the Vixen SS2K's dual axis tracking) were much less effective.

#44 GIR

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Posted 11 January 2014 - 04:08 AM

>> did you not read this thread?
Yes, I did.

For the user who pre-marked his DDM85 location on his driveway it sounded like 30-40 minutes for polar alignment, followed by 15 min for a 50 star point model followed by 5-8 min (times 2? if a meridian flip is needed) for a MLPT which is 30+15+2*10=65 min.

The reason I've restated the question is to confirm the above estimate.


Dave

The time needed setting up any system is very much dependent on the person who is doing it and what kind of setup he has.

Harel is settting up his system in 30 min (look at the CCD imaging thread) Somebody else might require more time. I'm having a permanent setup so can't give you a definite answer. However, have taken the system down and set it up so many times that should be able to do it in 30 min in any place.

P.S. DDM60 has a built in laser which is VERY helpful when doing the first rough polar allignment. Only people who don't have it say you'll not need it. Besides polar allignment with ASA mounts will take far less time than 30-40min.

#45 Waldemar

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Posted 11 January 2014 - 09:37 AM

Rough PA takes me less than a minute with the laser on my DM60Pro
It is done with the “naked” Mount, without scope or weights
For balancing I made marks and stops on the dovetail, depending on what camera and setting I use. so that does not take very long either. PID settings are previously done for different set-ups and stored in the software, as are the pointingfiles. You can make a set of pointingfiles for different areas in the sky as well as in the world and store them for later use. Next step will be "go-to" a star at app. the same altitude, but in the Southern sky to align with, center it with the AltAz adjustment (tilt) screws, enter....ready to go in let's say 10 min, after initial set up of tripod and Mount with scope.
The accuracy, speed, stillness and capability of this mount is totally unbelievable until you have experienced it yourself... This DDM60Pro is the best piece of equipment that ever happened to me.
After the initial brainfarts :o from my side and the for me rather steep learning curve :confused:, I can truly say that this is premium high end hard- and software.
As far as guiding goes: guiding with camera’s is always seconds too late doing the corrections. The DDM checks realtime 100 times per second between the "IS" and the "SHOULD BE" position, and corrects accordingly. This of course is done without optics, by comparing absolute decoder positions (0,02" accurate !!).
So however well you may be able to guide, you are just always too late: after the fact... seconds!
NO back-lash, NO PE, If you need really accurate tracking, just use a 3 star polar-alignment, that will take a few minutes longer
With DDM your scope is directly connected to the motor axes without any gearing in between. Think of that: how incredible is it to construct a powerful motor making 1 rev per 24 hours ...

So... just for what it is worth.

Regards, Waldemar

#46 TerraPassenger

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Posted 11 January 2014 - 10:08 AM

Thanks very much for the time estimates for portable setup.

There's a few youtube videos - including this one by Harel http://www.youtube.c...h?v=GULVyAinFKA - showing how amazingly fast and quiet the DDM60 is. One of the few drawbacks I've heard is that the mount is hard to set up in the field; perhaps so, but it sounds like once you've mastered the basics of setup, remote setup of the DDM60 isn't too much different than for other mounts.

And - a minor thing - I really like the red color of the mount! Paired with the OS Veloce RH 200, it makes quite a pleasing package.

#47 GIR

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Posted 11 January 2014 - 10:44 AM

And - a minor thing - I really like the red color of the mount! Paired with the OS Veloce RH 200, it makes quite a pleasing package.


Will certainly agree with that statement :grin:

P.S. paying a bit extra for the Pro version is absolutely worth it. ASA mounts slew so fast and quiet that you don't want all kinds of cables hanging around in the dark.
See the difference on my Flickr page by comparing ASA DDM60 Pro and Losmandy G11 setups.

#48 Waldemar

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Posted 11 January 2014 - 11:48 AM

I think everything paired with this mount makes a very pleasing package!
And yes, it takes a bit of effort to find your way through the software, but what a reward!
:thankyou::jump: , Waldemar

#49 WadeH237

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Posted 13 January 2014 - 09:17 AM

A pointing model won't do a thing for declination drift. A T-point assisted polar alignment will. The go-to alignment doesn't do squat for tracking.


A pointing model by itself won't.

But many of the solutions that use a pointing model also correct for declination drift. As mentioned, Pro Track does. So will the upcoming APCC Pro. I believe that the 10Micron mounts also use the pointing model to correct for declination drift.

#50 Per Frejvall

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Posted 13 January 2014 - 04:39 PM

10Micron mounts use a complex term model with up to 100 underlying points. The calculation result in a number of complex terms that model the sky.

The model is used for pointing and tracking. Tracking takes place in both Ra and Dec, so it is not merely compensating for declination drift.

/per






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