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Equipment Discussions >> Mounts

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SL63 AMG
scholastic sledgehammer
*****

Reged: 12/21/09

Loc: Williamson, Arizona
Re: ASA DDM85X-SL - Keeps getting better new [Re: morten]
      #5489747 - 10/26/12 06:18 AM

Thanks for all the kind comments. I am really enjoying the ASA DDM85 mount. I think ASA has made a huge improvement to the DDM60 with the addition of fixed encoders on the axis. I had my DDM60Pro prior to this improvement and wasn't really happy with it, but I am sure the DDM60Pro is a fine mount with fixed encoders.

Knowing my experience with the DDM series mounts, I would not start out with a FL length greater than 1000mm. JJ, I think you may set yourself up for some frustration expecting to achieve 30 minute unguided subs at 2000mm FL right away. It's possible, but you'll need to really know the system well first.

I highly reccommend that you start with a simple telescope under 1000mm FL and first work on obtaining a very good polar alignment and achieving 5 minute unguided subs. As you get to know the software, particularly Sequence 9, plate solving and it's interaction with Autoslew, you can then venture into 10m subs and longer, Sometimes I still struggle with 20m unguided subs at 950mm FL f/3.6, yet I have on several occasions been able to shoot 20m unguided subs as 2432mm FL F/8 using my AT12RC.

At the longer focal lengths every error in your system is amplified greatly.

There are many things that come into play that can ruin an unguided sub, particulaly at higher FL. For example, I believe I have some flexure issues with my AT12RC which currently utilizes a FeatherTouch focuser. While I like the FeatherTouch focusers and MicroTouch controller system, I do not like the way it attaches to the AT12RC telescope and I believe it is likely the cause of both flexure and tilt in my current system.

I am replacing the FeatherTouch with an FLI Atlas focuser and a precision adapter for both my FLI ML8300, a future PL16803 and a TAK collimator.

It is critical to obtain precise collimation and it really isn't possible with my current focuser and even if I did obtian critical collimation there is no way to ensure the collimator and the camera chipset will both be aligned with the same optical axis.

Once I replace the focuser with the precision couplers for both the camera and the collimater, I am pretty sure this issue will be resolved and I'll be able to shoot 20-30m subs at 2432 with repeatable results.

So basically, I am telling you the mount is perfectly capable of the results you seek, but that doesn't necesssarily mean you will get those results everytime you setup your mount, but if you keep the FL shorter while you are learning how to deal with all of the issues you are sure to encounter, you'll keep your sanity.

Morten, it takes me about two hours to setup all my gear prior to sunset, then another two hours to get everything polar aligned to within 6-12 arc seconds. If I were only shooting subs at 5m, I could have everything polar aligned and a pointing model built in about 30 minutes, but since I leave my system setup for an entire new moon session, I tend to count the first night as a setup and test night and I am willing to spend most of the night tweaking the entire system for perfection.

If I had a permanent setup, I would dedicated several days to this process to get it perfect and then be done with it.

Of course you have to take into a account that I have done this process over and over again for almost two years now, so I am very good at setting up the system in a portable environment.

It takes time to learn the system, then more time to practice the process of setting it up and aligning everything in a repeatable without making a lot of mistakes.

Personally, I like the challenge. This whole astrophotography hobby is a very technically challenging endeavor and that is what keeps me interested.

JJ, congrats on your new mount. I just wrote some procedures for getting started with tuning the motors and balancing. You can find the information on the Yahoo group. Read it carefully and it will save you some time when you first setup your DDM60Pro. Getting the servo motors properly tuned and balancing the system using the provided tools is also critical to achieving long unguided exposres.

JJ, I notice you have a QSI683wsg camera. Since this camera has a pick off prism mounted in front of the filters, I highly recommend that you purchase a Lodestar camera to use for autoguiding at long FL. While the mount is perfectly capable of unguided exposres, having an OAG and autoguiding at FL's greater than 1500mm will ensure perfect results, especially for subs >=20m, such as may be necessary for Ha, SII, NII and OIII narrowband imaging.

I intend to purchase an OAG for use with my AT12RC for 30-40m subs. Although I have not yet tried autoguiding with the DDM series mounts, I have read about it and it seems to be straight forward and relatively simple to do.

Enjoy your new mount and let me know if you have any issues with which you need help.


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jjongmans
super member


Reged: 02/11/12

Loc: The Netherlands
Re: ASA DDM85X-SL - Keeps getting better new [Re: SL63 AMG]
      #5489763 - 10/26/12 06:52 AM

Hi Dave, I'm not completely new to astrophotography and I also know a few things about PID controllers, but it will be hard to get good results in the beginning. I already have the Lodestar, so I can switch to guided imaging if the unguided results are no good. I managed to get good results on a EQ6 with 2000mm FL. I upgraded my focuser with a Moonlite high resolution stepper focuser, so I can use FocusMax to autofocus in an automated setup with CCDAutoPilot.
I already read your procedures on the Yahoo group


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SL63 AMG
scholastic sledgehammer
*****

Reged: 12/21/09

Loc: Williamson, Arizona
Re: ASA DDM85X-SL - Keeps getting better new [Re: jjongmans]
      #5490302 - 10/26/12 02:02 PM

I understand. I apologize if I implied in any way that you were new to astrophotography. I only meant to imply that with the mount coming with a bit of a steep learning curve it may be less frustrating to get started using a shorter focal length telescope in the beginning.

I visited your web site. Not only are your images remarkable, but also quite informative about each of the objects displayed.

I hope you enjoy the new mount.


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jjongmans
super member


Reged: 02/11/12

Loc: The Netherlands
Re: ASA DDM85X-SL - Keeps getting better new [Re: SL63 AMG]
      #5490407 - 10/26/12 03:10 PM

Hi Dave, you don't have to apologize! I am new to it, I started 2 years ago. I really enjoy reading your stories about this DDM, I think I can learn a lot from your experiences! Keep up the good work

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orion69
scholastic sledgehammer


Reged: 05/09/10

Loc: Croatia
Re: ASA DDM85X-SL - Keeps getting better new [Re: jjongmans]
      #5490629 - 10/26/12 05:55 PM

Are there any differences or advatages between guided and unguided tracking (and vice versa) if mount is correctly polar aligned?
Why would I shoot unguided if I can guide (disregarding you don't have to worry about guiding star or seeing)?


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BPO
sage


Reged: 02/23/10

Loc: South Island, NZ
Re: ASA DDM85X-SL - Keeps getting better new [Re: orion69]
      #5490877 - 10/26/12 09:11 PM

If you already have a good geared mount and guiding setup, there is probably little reason to ditch it in favour of one of these direct drive mounts, unless you really want to get rid of the guiding rig.

For a new setup, it makes a lot more sense. Once the user gains the necessary experience and has trained the mount, an external guiding rig becomes unnecessary; Indeed, counter-productive.

But it needs to be borne in mind that these mounts are a major step up in most ways. They are much closer to professional observatory technology than other kinds, and the demands on the user's ability and knowledge increase, at least at first, although the pay-off is significant.


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SL63 AMG
scholastic sledgehammer
*****

Reged: 12/21/09

Loc: Williamson, Arizona
Re: ASA DDM85X-SL - Keeps getting better new [Re: orion69]
      #5522888 - 11/16/12 01:09 PM

Quote:

Are there any differences or advantages between guided and unguided tracking (and vice versa) if mount is correctly polar aligned?
Why would I shoot unguided if I can guide (disregarding you don't have to worry about guiding star or seeing)?




I believe the advantages are significant.

With this mount, you have no backlash, no periodic error and without guiding, you eliminate a whole series of other potential issues, such as difficulty finding a guide star for long FL image. You eliminate issues such as how to guide, with an off-axis guider or a guide scope that may have flexure issues. Where do you place the guide chip, in front of or behind the filters, such as SBIG's cameras.

Certainly, guiding is not impossible, but I think it is a challenge in and of itself for beginners. So if you are going to spend hours learning how to setup and autoguide and solve all the nuances surrounding autoguiding, why not learn this mount and eliminate the need to autoguide altogether?

Then, once you have learned the mount and you decide, heck, I'm bored and want to learn something new, you can still autoguide using this mount!

In fact, I am going to learn to do it with my AT12RC so that I can take very long NB guided exposures at 2432mm focal length.

The joy is, however, that when using my ASA N10 or a small refractor, or even the AT12RC for exposures of 20m or less, I don't have to autoguide.

My polar alignment right now is >6 arc seconds error in RA and 6-8 arcseconds of error in DEC.

I can turn on the mount and start a 5 minute image and get perfect stars zoomed to 8x full resolution without even running MLPT.

Seriously, that's amazing.


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korborh
professor emeritus
*****

Reged: 01/29/11

Re: ASA DDM85X-SL - Keeps getting better new [Re: SL63 AMG]
      #5523463 - 11/16/12 09:02 PM

Auto-guiding is actually quite simple to do. Also finding guide-star in OAG is easy with calibrated FOV and planetarium software.
What is perhaps much harder is to maintain delicate and large pointing models and tune a complicated open loop system and hope that un-guided works


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SL63 AMG
scholastic sledgehammer
*****

Reged: 12/21/09

Loc: Williamson, Arizona
Re: ASA DDM85X-SL - Keeps getting better new [Re: korborh]
      #5523516 - 11/16/12 09:51 PM

Quote:

Auto-guiding is actually quite simple to do. Also finding guide-star in OAG is easy with calibrated FOV and planetarium software.
What is perhaps much harder is to maintain delicate and large pointing models and tune a complicated open loop system and hope that un-guided works




There is no hoping about it. The proof is in the pudding.

A single 30 minute unguided luminance -35c binned 1x1 900mm FL F/3.6 unprocessed.

Image taken 39 minutes ago. No MLPT, just point and shoot.

Will your mount put this target dead center on every slew and stay there for 30 minutes without moving a pixel?

Incidentally, my current polar alignment error is <=6 arcseconds in RA and <=12 arcseconds in DEC. it's unlikely you can even get your mount that closely polar aligned.

Let's not forget that Autoslew corrected for the polar alignment error, tube flex east and west, collimation error and synch offset and sent corrections to the mount in real time.





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korborh
professor emeritus
*****

Reged: 01/29/11

Re: ASA DDM85X-SL - Keeps getting better new [Re: SL63 AMG]
      #5523801 - 11/17/12 02:19 AM

I routinely take 30min subs with <2" FHWM stars, 100% yield at 2800mm FL with OAG and AP1200 mount. The mount is 30" Polar aligned RA/DEC and I did not tweak further as it is not necessary.
Plate-solve + sync + slew lands on each target dead on center of chip, only a few pixels off. I don't use modeling - just simple plate-solve + re-slew.
Un-guided may be useful when one wants to take many images per night e.g. supernova survey. Un-guided is also more forgiving with refractors where flexure is minimum. With long FL mirror based scopes, flexure is large and less accurately modeled.
I have not yet seen an un-guided raw image with <2" star FWHM in 30min subs.


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jjongmans
super member


Reged: 02/11/12

Loc: The Netherlands
Re: ASA DDM85X-SL - Keeps getting better new [Re: korborh]
      #5523880 - 11/17/12 06:48 AM

It would be strange if you couldn't accomplish good autoguided results with an AP1200. Same counts for the DDM85.
The reason I don't want to autoguide is because I'm using automation software like CCD AutoPilot and I like to refocus during my subframes. It takes time to reacquire the guidestar and needs time to settle, I don't like that. If you guide with a low min. motion setting, you'll guide on the seeing with lots of unneeded corrections. If you use a high min. motion setting, you'll be too late to correct the error. So with autoguiding you constantly need to adjust the parameters to have optimum guiding, something I don't want to do in an automated setup.
So I think there won't be a big difference in results from an autoguided and unguided setup, it's just another way of working.


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korborh
professor emeritus
*****

Reged: 01/29/11

Re: ASA DDM85X-SL - Keeps getting better new [Re: jjongmans]
      #5524147 - 11/17/12 10:57 AM

The only autoguide settings I have needed to change (only sometimes) is aggressiveness to match the seeing. One does not need to mess with other settings much at all if the system does not change.

To get the best long exposure data, it is desirable to use closed-loop guided systems and not open loop. Also. I am not sure un-guided using these mounts is any easier than autoguiding.


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orion69
scholastic sledgehammer


Reged: 05/09/10

Loc: Croatia
Re: ASA DDM85X-SL - Keeps getting better new [Re: korborh]
      #5524849 - 11/17/12 06:30 PM

I don't really care if I guide or not, it's the result I'm interested. If guiding is not the problem (and so far it never was) I don't see why I wouldn't use guiding with this excellent mount. Problem is I don't have permanent setup and fast polar aligning is required.
Btw, if you look at my images you'll see they are all 30 min subs except one...

Edited by orion69 (11/18/12 09:33 AM)


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