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Equipment Discussions >> Mounts

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Domerman
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Reged: 07/21/07

Loc: PA
Do direct drive mounts really not require guiding?
      #5709928 - 03/03/13 04:35 AM

So I'm looking to get a portable high-end mount for 10k or less that can haul perhaps something not much larger than a TEC 140. I want this mount pretty much only for AP, however, I will not have a permanent setup and will require a light mount that is not too difficult to setup. I really would love to avoid auto-guiding if possible and I was wondering if these new ASA mounts are as accurate as they really say? I understand that ultimately one will need to guide to eliminate for atmospheric abberations, but as far as mechanical corrections are concerned, the periodic error on these mounts is incredibly low. This is very exciting, as I would only need to focus on polar aligning and letting the scope do the rest. I know there are true and tested mounts out there in this class like AP and Paramount, however, these are for a lack of a better word...bulky and still require guiding and plate solving....or am I completely wrong in all of this?

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Footbag
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Reged: 04/13/09

Loc: Scranton, PA
Re: Do direct drive mounts really not require guiding? new [Re: Domerman]
      #5710152 - 03/03/13 09:02 AM

Any mount that doesn't require guiding is going to require you to build up a pointing model. This takes a good amount of time, and isn't as conducive to a portable setup as one would hope.

I may be wrong about this, but it isn't really the direct drive technology as much as the encoders that can allow you to forgo guiding. The AP 1600 has absolute encoders. Maybe the 1100 will offer it, but I don't see the Mach 1 getting them soon.

For a permanent setup, I'd buy an ASA in a second. For portable, I'm thinking AP is the best option; just understand that you'll be guiding. I've worked my guiding routine into my PA setup and can probably get setup in 30m with them.


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orlyandico
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Re: Do direct drive mounts really not require guiding? new [Re: Footbag]
      #5710268 - 03/03/13 10:08 AM

Ray says that APCC will allow even non encoder AP mounts to shot unguided for tens of minutes. Its not the direct drive, its the pointing model.

That said a quick fix is to buy a standalone guider like an SG4 or a Lacerta MGEN. This would let you dispense with the PC.


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neptun2
scholastic sledgehammer


Reged: 03/04/07

Loc: Bulgaria
Re: Do direct drive mounts really not require guiding? new [Re: orlyandico]
      #5710950 - 03/03/13 04:30 PM

The direct drive means that you have no periodic error. This helps. The other high end mounts that are not direct drive have very low periodic error but there is some. Encoders can definitely help to avoid the need of guiding if they are very high precision but the ASA is for me the best combination of technology at one place. They have something called MLPT (Local multi precision tracking) which some kind of pointing model specific for the object that you will image. With this i do not see any reason to guide. See more details here:

http://www.astrosysteme.at/eng/software_mlpt.html

Also the ddm60 is definitely portable and relatively easy to setup from what i have read.


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Domerman
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Reged: 07/21/07

Loc: PA
Re: Do direct drive mounts really not require guiding? new [Re: neptun2]
      #5711228 - 03/03/13 06:55 PM

So what is a pointing model and can it eliminate the need for guiding? What do I need to make a pointing model?

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neptun2
scholastic sledgehammer


Reged: 03/04/07

Loc: Bulgaria
Re: Do direct drive mounts really not require guiding? new [Re: Domerman]
      #5711471 - 03/03/13 08:59 PM

The idea behind ASA's MLPT is that you tell the software which object you will image and how many and how long exposures you will take and after this the mounts points o the object, calculate how long it will travel the sky till the exposures are completed, takes several exposures during it's path, plate solve them and see exactly what kind of errors you will have while imaging. This allows later these errors to be corrected. This allows to compensate for practically all mechanical errors including flexure, mirror flop in SCTs and all other. That's why you do not need guiding.

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orlyandico
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Re: Do direct drive mounts really not require guiding? new [Re: neptun2]
      #5711568 - 03/03/13 09:50 PM

Steve, TheSkyX can produce a good pointing model. Same for the ASA software and the upcoming APCC.

The key requirement is that your periodic error must be zero or pretty close to it. Then the pointing model only needs to compensate for flexure, mirror flop, atmospheric refraction, etc.

Now a worm-driven mount won't have zero periodic error, but the decent ones (Paramount, AP) can get the periodic error down to sub-1" (0.5" or thereabouts) peak-to-peak. So if you are imaging at say 2" / pixel (typical for a short to mid-FL refractor) then you don't need to guide because the periodic error is small enough.

Note that you still need the pointing model, long unguided exposures aren't just about having small (or zero) PE.

Ah - and, to use this pointing model, you need a PC with appropriate software. At this point the advantage of AP over Paramount ("you don't need a PC!") goes away, because you will need a PC to work this magic.

IMHO, a better solution is to just buy a stand-alone guider. After all the reason most people don't want to guide, is because they don't want to use a PC. The pointing model solutions all require a PC, so the only advantage is you're not subject to wind or clouds screwing the guide star.

But if your goal for not wanting to guide is convenience, having a PC along is not convenient.


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frolinmod
Carpal Tunnel


Reged: 08/06/10

Loc: Southern California
Re: Do direct drive mounts really not require guiding? new [Re: neptun2]
      #5711590 - 03/03/13 10:01 PM

@neptun2, that's cool. I like that. However, that does assume everything is 100% repeatable which is not always the case, particularly with SCT mirror flop. I consider all these cool schemes as being somewhat analogous to "PEC for tracking." They're quite helpful, but don't expect perfection. They may even be "good enough" for lower focal lengths or short exposures, but eventually you're probably going to need a guider. Might as well figure that into your plans from the beginning. These things do make the guider's job easier, allow it to make corrections less often, make longer exposures hence use dimmer guide stars, etc. Good to have for sure.

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Domerman
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Reged: 07/21/07

Loc: PA
Re: Do direct drive mounts really not require guiding? new [Re: frolinmod]
      #5711626 - 03/03/13 10:16 PM

Wait, but if I use a CCD, I will need a computer no matter what. I have no plans of using a DSLR. I want to use a mono camera with filters for narrow band imaging.

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orlyandico
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Re: Do direct drive mounts really not require guiding? new [Re: Domerman]
      #5711627 - 03/03/13 10:18 PM

Err.. true. In which case I don't really see the benefit of no guiding. The hassle involved with setting up and building the pointing model VS not needing to find guide stars.

But if your situation is such that there is strong wind and you're losing guide stars, then imaging under such circumstances is going to be a challenge anyway.

Although that said the ASA mounts supposedly can also compensate for wind gusts. That's something they have over the encoder-less mounts.


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Domerman
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Re: Do direct drive mounts really not require guiding? new [Re: orlyandico]
      #5711634 - 03/03/13 10:22 PM

So if strong winds are not an issue, then I might as well go the much cheaper route and get a portable Mach1 mount or Temma or something along those lines and use a 50mm guide scope?

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Domerman
Just Lucky, I Guess.
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Reged: 07/21/07

Loc: PA
Re: Do direct drive mounts really not require guiding? new [Re: Domerman]
      #5711643 - 03/03/13 10:26 PM

Also, I'm not quite understanding, if the encoders are allowing for almost no PE, then why do I need to guide? I thought guiding was just for wind and PE inherent to a mount. What is this business about pointing models?

EDIT: I am guessing the encoders cannot account for flexure and things of that nature, thus is the reason you need pointing models. Answered my own question, I think..

Edited by Domerman (03/03/13 10:29 PM)


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orlyandico
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Re: Do direct drive mounts really not require guiding? new [Re: Domerman]
      #5711648 - 03/03/13 10:29 PM

Because sidereal rate isn't.

Due to atmospheric refraction at different elevations (altitude) the speed is not precisely the sidereal rate.

Also with an SCT, the mirror moves around as you point to different objects, causing image shift.

But in answer to your question... yes a good worm-drive mount and a guider is what I'd do. In fact that is what I have done. A guider calibrate only takes a short time, and the Mach1 is the lightest mount you can get that's decent.

I would stay away from the Temma if I were you... Taks are overpriced for what you get (no PEC! and the EM200 is only rated +/- 5" I think - so no way to get that down).

My Mach1 is about 3.5" p-p when east-heavy, and 6" p-p when west-heavy. PEM gets this down to 0.4" / 0.8".

You can't get anywhere close to 0.8" p-p with an EM200 because there's no PEC. Tak NJP (and I suppose EM400) can get about 1.5" p-p but those are heavy. An NJP is cheaper than a Mach1 if you can find one. But remember.. with Temma there's no GoTo from the handset. You need to command GoTo's from a computer.

And coming from a CGEM like I did... you will be amazed and shocked at the primitive mount modeling of AP and Tak. Only one-star aligns are supported, so your polar alignment has to be dead-on, otherwise GoTo's will be inaccurate.

but then again you need a dead-on polar alignment to image, so...


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Domerman
Just Lucky, I Guess.
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Reged: 07/21/07

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Re: Do direct drive mounts really not require guiding? new [Re: orlyandico]
      #5711651 - 03/03/13 10:31 PM

Quote:

Because sidereal rate isn't.

Due to atmospheric refraction at different elevations (altitude) the speed is not precisely the sidereal rate.

Also with an SCT, the mirror moves around as you point to different objects, causing image shift.

But in answer to your question... yes a good worm-drive mount and a guider is what I'd do. In fact that is what I have done.




Oh ok! That makes perfect sense now!


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shams42
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Reged: 01/05/09

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Re: Do direct drive mounts really not require guiding? new [Re: Domerman]
      #5711683 - 03/03/13 10:50 PM

The Tak mounts are ideal for portable use, though, because of the uber-accurate polar scope. I can set up and polar align my NJP in less than 10 minutes and then shoot 20 minute subs all night long without losing a single one (autoguided, of course).

If I ever move to a more permanent setup I will probably get a Paramount MX. Until then, I really like the Tak.


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orlyandico
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Re: Do direct drive mounts really not require guiding? new [Re: shams42]
      #5711693 - 03/03/13 10:57 PM

The trouble with the new Taks is that they aren't palatable cost-wise. Paying almost the same money for an EM200 vs Mach1 just for the polar scope is... not good sense.

Of course a used Tak NJP has got to be the deal of the year, if you can find one. A new EM400 at $10400... not so much. You can get an AP1600 for that kind of money.


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korborh
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Reged: 01/29/11

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Re: Do direct drive mounts really not require guiding? new [Re: orlyandico]
      #5711715 - 03/03/13 11:13 PM

I have to say there is something quite elegant about the Tak mounts that they achieve such accurate performance with much smaller gears/bearings than AP/SB. And the polar scope is very nice calibrated from the factory. The price is too high unfortunately.

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Domerman
Just Lucky, I Guess.
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Reged: 07/21/07

Loc: PA
Re: Do direct drive mounts really not require guiding? new [Re: korborh]
      #5711815 - 03/04/13 12:43 AM

So in the not to distant future I see myself using a Mach1GTO with a TEC 140 and auto-guider. I think the AP should be able to handle this load appropriately. I'm assuming my C11 for visual use would be well handled by the the Mach1GTO, as my CGEM handles it fairly well..

Is there any other portable GEM I should consider in this price range?

I really want to emphasize portability here...so the CGE Pro and similar are off the table.

Edited by Domerman (03/04/13 12:44 AM)


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orlyandico
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Re: Do direct drive mounts really not require guiding? new [Re: Domerman]
      #5711820 - 03/04/13 12:51 AM

The Mach1 will handle the C11 for imaging without any problems.

There simply isn't any other mount in that weight class (30 lb for the head) that can match the Mach1. The EM200 weighs more and carries less. I also looked at the CGE Pro for less money but it's very heavy. The G11 weighs more and is less capable. Not sure how much the ASA DDM60 weighs but it costs more. Ditto for the Paramount MX - more capacity, arguably better payload for the dollar, but also heavier. Tak NJP also quite heavy.

Well there is one alternative.. AP 1100 (the 900 replacement). Which weighs less than the 900. The 900 weighs 55 lb total and splits into two parts. Each part weighs a bit less than a Mach1.

So the question for you is.. what is lightweight? 30 lb? or pieces that weigh 30 lb?


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neptun2
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Reged: 03/04/07

Loc: Bulgaria
Re: Do direct drive mounts really not require guiding? new [Re: korborh]
      #5711821 - 03/04/13 12:53 AM

Well about the ASA MLPT - i read that people get 40 minute exposures at over 2000mm focal length so i don't think that it is usable only with short focal lengths. Another idea of the MLPT is that you don't need to create big pointing model when you use it. You make basic pointing model with several points so that you can make your polar alignment and goto accuracy is good but after that the MLPT creates local pointing model for the object that you will image. I always have laptop with me on the field so that is not a problem.

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