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Ovision Worm Upgrade for Losmandy Mounts

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#1 Steve Saturn

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Posted 12 November 2008 - 12:28 AM

I've been reading with great interest about the Ovision worm gear upgrade available for Losmandy mounts. Since they've been available for some time now, I wanted to solicit the thoughts of those of you who have installed the Ovision worm gear or have had experience with it. Here are a few questions that come to mind:

1) Is the Ovision upgrade living up to your expectations?
2) Are you experiencing a measureable improvement in periodic error that that you can clearly attribute to the upgrade?
3) If you are an astrophotographer, can you clearly see an improvement in your images that you could attribute to the upgrade?
4) Is there a U.S. distributor for the Ovision worm gear? If not, how would you describe your experience with ordering from Ovision?
5) How would you rate your customer support on a scale of 1 to 10?
6) How would you rate the ease of installation on a scale of 1 to 10?
7) Knowing what you know now, would you do it over again?

Thanks for any thoughts!

Steve

#2 xtian

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Posted 12 November 2008 - 06:37 AM

Hello Steve

I try to comment my experience...

First, you have to measure the original PE of your G11. The original worm made with brass can give you an acceptable PE.

For example, my original PE is +- 4.5". But I have a period of 76 seconds. It not normal and it's not perfect, but I am astrophotographer and the guiding is correct.
So I didn't change my original worm.

Generally, the Ovision worm gives the same PE (+- 4 or +- 5") but without harmonic and the period is longer, about 240 s. So the Ovision curve is very "discreet"..

This is an example :

In blue my original curve (= original worm) and in yellow the Ovision curve.
My curve gives an harmonic period of 76 seconds :


Posted Image

I hope that my comments are clear...


Christian

#3 Steve Saturn

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Posted 12 November 2008 - 12:43 PM

Hello Christian,

Thank you for your reply. At present, I'm not sure that I have a good way to measure my current periodic error (any suggestions would be appreciated). If I understand your data correctly, your plots are saying that while the frequency of your worm gear's periodic error may be greater than that claimed by Ovision for their worm, the amplitude of the deviation from ideal is the same.

So if I were to relate this to what I might see in astrophotos taken from mounts producing each of these plots would be that while your original worm gear would produce more "squiggles" in the star trails, the size of the "squiggles" would essentially be the same as those that would result from using the Ovision worm gear. And if I'm following you correctly, this would essentially produce astrophotos of the same quality.

Am I on the right track? Thanks for your help!

Steve

#4 xtian

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Posted 12 November 2008 - 01:27 PM

Yes Steve

My worm produce a star trail more squiggly.
The frequency is higher but the amplitude is the same.

I am lucky, I think that I got an original worm not too bad... But I am interested to reduce the 76 seconds harmonic.

What is the consequence of the squiggles effect for astrophoto ?
In my case, here is no consequence. Because I use a C8 at F7 and the guiding is correct, in spite of the squiggles effect..
During a guiding the guide star deviation is acceptable (max +- 0.5") :

Posted Image

For the moment it's enought for my deep sky applications... hi


I think that the worm Ovision is necessary if the original worm is not acceptable (ex : no periodic curve, or very important amplitude..).

And may be if you work with long focales, or in narrow band with a long guiding integration time (ex : 10 secondes with Sbig CCD in H alpha..).



Christian

#5 blueman

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Posted 12 November 2008 - 02:33 PM

Hi,
I too installed the OVision in my G-11. I also had good PE with the original Brass Higg Precision worm. But I had the 76 error as well.
I got pretty good guiding with the original system and worm. But I wanted to get a better PE curve and less amplitude.
After I installed and adjusted the OVision, I found that guiding was improved dramatically. I notice that guide corrections are not continuous and the movement is less. So there are long periods when there is no real correction required. Also, I see much improved stars when exposures are 10 minutes or longer. Stars are round and crisp.
The cost of $500 is not cheap, but if you are doing Astrophotography, it is a cheap way to get your mount performance improved to the point that it rivals mounts costing 2x as much.
Also, the Ovision is much easier to set the lash. It is really a big improvement overall.
Blueman

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#6 Steve Saturn

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Posted 12 November 2008 - 03:20 PM

Thank you very much Christian and Blueman. Your answers go a long way toward answering specifically what I might expect with regard to improvement of my astrophotographs after installation of the Ovision worm gear. All the posts that I've read until now certainly suggested that there would be an inmprovement, but I wasn't very clear on how that might translate into better astrophotography.

Is there a good link that I could refer to to explain the basic premise of the 76 harmonic error that you both describe?

Is there a relatively simple way that I could evaluate my periodic error without investing a fortune in software? I'd like to be able to plot my PE as you've done Christian, but I'd rather not spend more than say $50 to $100 on software. Free would be even better! :cool:

Blueman, did you purchase your Ovision gear assembly directly from the manufacturer or is there a domestic distributor? Were installation instructions included (in English), my French is not so good... :ohmy:

Thanks again guys!
Steve

#7 blueman

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Posted 12 November 2008 - 04:39 PM

Hi,
Well, there are lots of post concerning this on the Yahoo Losmandy Users group, but I believe that some of it is in the files section and you would have to join, which is not a big deal.
You can download PHD guiding software (free) and PHDAnalyzer (free) and PECPrep (free).
Then you can set up the guiding with PHD and then turn off guiding corrections and logging on and this will create a log of the movements of the guide star.
Then you can open the log file with PECPrep and it will give you all the data, such as +- arc sec PE and even the frequency chart showing the 76 sec error as well as other errors in the system.
This will show you what you have now and then you can decide what to do and it will cost nothing.
:D
Blueman

#8 xtian

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Posted 12 November 2008 - 04:45 PM

Steve

I use PEAS, a free software wrote by Jan Greener.
This soft makes the differents curve and the harmonic analysis of the mount.
It works with differents data, IRIS, AstroArt, K3CCD or Guidedog.

You are right, before to spend $500 is necessary to evalute the PE with the original worm.

As Blueman, my stars are round and crisp after a long exposure, but the guiding corrections are more frequent.

Christian

#9 Steve Saturn

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Posted 12 November 2008 - 06:04 PM

Thanks once again Christian and Blueman, you've been immensely helpful. I've always wanted to evaluate my mount's PE and now you've provided the tools to get me started. Once I have some results I'll be back to solicit your thoughts in evaluating them. Thanks again!

Steve

#10 Steve Saturn

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Posted 12 November 2008 - 06:17 PM

One more question does come to mind. :grin:

Of the software that you've both listed (PECPrep, PHDAnalyzer, PEAS), how critical is it that your mount be perfectly polar aligned before a decent PE analysis can be performed? Can the software differentiate between periodic error and rotational error?

Steve

#11 Chris Shillito

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Posted 13 November 2008 - 06:16 AM

One more question does come to mind. :grin:

Of the software that you've both listed (PECPrep, PHDAnalyzer, PEAS), how critical is it that your mount be perfectly polar aligned before a decent PE analysis can be performed? Can the software differentiate between periodic error and rotational error?

Steve


A decent Polar alignment is useful, particularly as it will reduce star drift in declination. To get a good frequency analysis you want to capture at least 6 cycles of data so you're star needs to stay in view during this period so its good to reduce such drift effects.

Any rotation effect will naturally affect the data but this should just appear as another low frequency signal in the spectrum so shouldn't compromise any analysis. With PECPRep you can apply filters in to remove low frequency signals from the time domain graph.

PECPrep and PEAs will correct for any linear drift in RA caused by tracking problems.

If anyone wants to know more about PECPrep in particular then see
http://eq-mod.source...et/ppindex.html There is a pdf document there and a link to the sourceforge download.

Note that PECPrep was originally developed for EQ mounts as part of the EQMOD Project. This said the mount characteristics and key mechanical periods etc are all stored within external text files that can be edited to suit other mount types.

PECPrep can accept log files from PHD, K3CCDTools, MaximDl, Metaguide, GuideMaster and PERecoder. PERecorder is a free utility for PE capture using a webcam on any ASCOM compatible mounts (see http://perecorder.wikidot.com/ )

Chris (PECPrep author)

#12 blueman

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Posted 13 November 2008 - 11:23 AM

PECPrep is actually better than PEAS and both being free, I would try them both.
PECPrep has more information for analysis than PEAS. But I use both programs.
Blueman

#13 Steve Saturn

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Posted 13 November 2008 - 11:06 PM

Hi Chris,
Thanks for the great info. Based on what I'd read so far, I had assumed that PECPrep could filter out the effects of some degree of poor alignment (as you said, as long as it isn't too far off). I'd like to gather data using the setup that I use to guide, so since PecPrep appears to work in conjunction with PHD Guiding it looks like this would be ideal. Are there default values for the G11 in the program or will I need to find them elsewhere (any suggestions)? Thanks for your help!


Blueman,
Thanks again for your help!


Steve

#14 Steve Saturn

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Posted 13 November 2008 - 11:13 PM

Not that I'm ready to plunk down money for the Ovision upgrade without doing some testing first, but I found this to be an interesting read for those of you who may be considering it.

Steve

#15 blueman

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Posted 14 November 2008 - 01:27 AM

You have to input the parameters in PECPrep. They are available.
Blueman

#16 Charlie Hein

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Posted 14 November 2008 - 09:43 AM

Chris - can you explain exactly what number you're looking for in the "steps per full rotation" figure on the PECPrep configuration screen? If it is stepper motor steps per full rotation of the worm gear then what should a Gemini user put in there since the Gemini uses servos?

Charlie

#17 Chris Shillito

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Posted 14 November 2008 - 09:44 AM

Are there default values for the G11 in the program or will I need to find them elsewhere (any suggestions)? Thanks for your help!


Hi Steve,
There are no defaults for the G11 but you can define new mount types within PECPrep and these are stored for future use so its a one time operation. For analysis all you really need to know is the worm period (so it can graph it nicely and do stacked cycle display). There are other parameters it prompts for such as number of RA gear teeth and steps per full rotation but these are for building and synchronising correction curves for use with our EQASCOM driver (EQ mounts only so far). You can probably set these to any non zero value. In addition to a "name" which will appear in the PECPrep mounts menu, there is a "tag" parameter as well, just set them both to G11. The tag is used to locate a list of known significant period markers in the marks.def file. This feature is entirely optional but to add markers just edit the file in notepad - the format should be obvious when you see it.

I believe there is a slight bug at the moment in that once you've changed the mount parameters you need to deselect the mount and reselect it for the new parameters to take effect. This will be fixed on the next release.

Chris.

#18 Chris Shillito

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Posted 14 November 2008 - 11:22 AM

Chris - can you explain exactly what number you're looking for in the "steps per full rotation" figure on the PECPrep configuration screen? If it is stepper motor steps per full rotation of the worm gear then what should a Gemini user put in there since the Gemini uses servos?
Charlie


Hi Charlie,

PECPrep was designed with two two basic functions in mind, the analysis of PE, and the preparation of a PEC curve for use by EQASCOM. The total motor steps and gear teeth parameters are strictly for the PEC side of things and provide a way to synchronise correction curve playback with the mount encoder position. For Gemini user's this function of PECPrep has no current application.

For PE analysis (in both frequency and time domain) these parameters are not relevant. I think the code rejects a value of 0 though but using the same values as are shown for any the EQ mounts would be a safe option.

Chris.

#19 Steve Saturn

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Posted 14 November 2008 - 07:59 PM

Thanks a million for your help Chris. I'm looking forward to trying this out.

Steve

#20 blueman

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Posted 15 November 2008 - 01:17 PM

Steps
2592000
Total gear teeth
360
Worm period
239

These are all you need to create a G-11 for PECPrep.
Blueman

#21 rsbfoto

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Posted 15 November 2008 - 04:21 PM

Chris - can you explain exactly what number you're looking for in the "steps per full rotation" figure on the PECPrep configuration screen? If it is stepper motor steps per full rotation of the worm gear then what should a Gemini user put in there since the Gemini uses servos?
Charlie


Hi Charlie,

PECPrep was designed with two two basic functions in mind, the analysis of PE, and the preparation of a PEC curve for use by EQASCOM. The total motor steps and gear teeth parameters are strictly for the PEC side of things and provide a way to synchronise correction curve playback with the mount encoder position. For Gemini user's this function of PECPrep has no current application.

For PE analysis (in both frequency and time domain) these parameters are not relevant. I think the code rejects a value of 0 though but using the same values as are shown for any the EQ mounts would be a safe option.

Chris.


Hi Chris,

Very good program, but I have a problem in making it run eg. spoecify a G11 mount. I always get this error

I have tried with different values but always that error pops up and then the program closes.

Thanks for any comment.

#22 Steve Saturn

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Posted 15 November 2008 - 04:35 PM

Thanks for the info Blueman!

Steve

#23 rsbfoto

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Posted 15 November 2008 - 07:06 PM

Chris - can you explain exactly what number you're looking for in the "steps per full rotation" figure on the PECPrep configuration screen? If it is stepper motor steps per full rotation of the worm gear then what should a Gemini user put in there since the Gemini uses servos?
Charlie


Hi Charlie,

PECPrep was designed with two two basic functions in mind, the analysis of PE, and the preparation of a PEC curve for use by EQASCOM. The total motor steps and gear teeth parameters are strictly for the PEC side of things and provide a way to synchronise correction curve playback with the mount encoder position. For Gemini user's this function of PECPrep has no current application.

For PE analysis (in both frequency and time domain) these parameters are not relevant. I think the code rejects a value of 0 though but using the same values as are shown for any the EQ mounts would be a safe option.

Chris.


Hi Chris,

Very good program, but I have a problem in making it run eg. spoecify a G11 mount. I always get this error

I have tried with different values but always that error pops up and then the program closes.

Thanks for any comment.


Hi Chris,

Well managed to get a G11 into the program. Just took an existing EQ... file and changed the parameters for a G11 and values were accepted :smirk:

Look like there is a kind of bug when trying to save a new file.

Thanks

#24 blueman

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Posted 15 November 2008 - 09:54 PM

No problem Steve, that should get you started.
Blueman

#25 Chris Shillito

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Posted 16 November 2008 - 08:23 AM


Hi Chris,

Very good program, but I have a problem in making it run eg. spoecify a G11 mount. I always get this error

I have tried with different values but always that error pops up and then the program closes.

Thanks for any comment.


Hi Chris,

Well managed to get a G11 into the program. Just took an existing EQ... file and changed the parameters for a G11 and values were accepted :smirk:

Look like there is a kind of bug when trying to save a new file.

Thanks


Hi Rainer,

Good to here you've found a way to get it working. What were you doing when the error box appeared - did it occur when you hit the "apply changes" button ? I'd like to chase down this problem if I can.

For the next release I'll add in some defaults for the G11 based upon Blueman's recommendations. If anyone can give me a list of known significant mount periods/frequencies (and brief descriptions) then I'll add those as well.

Chris.






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