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Losmandy OPWB

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#1 tboss70

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Posted 10 November 2012 - 07:38 PM

Is there any newer user info on the OPWB? I've read a few older articles but was looking for some new feedback.

My latest autoguiding attempts get me 10 minutes with almost perfectly round stars using the stock G11G2 so I'm not sure I need to invest the money but was curious. Thanks,

#2 gezak22

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Posted 11 November 2012 - 01:15 AM

Is there any newer user info on the OPWB? I've read a few older articles but was looking for some new feedback.

My latest autoguiding attempts get me 10 minutes with almost perfectly round stars using the stock G11G2 so I'm not sure I need to invest the money but was curious. Thanks,


The worm period on the G11 is 4 min, right? So if you can guide for one worm period with round stars then you should be able to guide for x worm periods with round stars, provided you are properly polar aligned, and that there is no flex. Are you sure you are not limited by field rotation, flex, ...? What does your PHD graph look like?

Having said that, I upgraded the original worms of my GM8 with the OPWB, and I have found guiding to be much smoother. Since I didn't quantify my guiding performance back then, I can't comment on how big the improvement was, but I get ~1.2 arcsec or better RMS these days with very few spikes in my guide curve in PHD.

I do have a small complaint about the OPWB. I bought two, one for RA and one for DEC. While the one on the DEC axis has zero backlash, the one on the RA axis has a lot. It's really not an issue as I leave my RA axis way off balance, so I never see the backlash in my guide curves. Still, it's odd.

And finally, I hear that for the G11 the Ovision worm is a nice step up from the Losmandy worm.

EDIT: Sorry, I just realized that you were asking about the OPWB, not about the high pres worm. With the OPWB, adjusting the worm position of the worm to reduce backlash is as easy as falling off a log.

#3 David Ault

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Posted 12 November 2012 - 01:34 PM

Todd,

When I purchased my G11G2 I got the OPWB along with it so, I can't comment on what the stock worm is like. With my OPWB I typically get PHD RMS values under 0.5 arc-seconds (below 0.2 RMS on the PHD graph with a 2.54 arc-second / pixel image scale). The OPWB does make it easier to adjust the backlash and the 76 second error due to misalignment of the worm blocks is non-existent. When you go to service your G11 you might wish you had the Ovision or OPWB, but I don't know if that alone is worth the purchase. The other reason you might consider upgrading is if you move to a longer focal length scope (usually adding weight at the same time). Then you might find that your tracking is not up to scratch and the OPWB might get you there.

What I would do is measure my actual error (this can be done with tools like PEMPro or just using the log data from PHD along with PECPrep or even a spreadsheet program). Or you can just get a good estimate from the RMS value on the PHD graph and adjust it for your image scale (you can use CCDCalc to plug in your scope / camera info to get that). A good tracking value depends on a lot of things, like what your image scale is, what the diffraction limit of your scope is and what your seeing conditions are like, but I'd say that if your tracking is less than half your image scale you should have no problems (assuming there are no problems like differential flexure). For example, my typical image scale is 2.27 arc-seconds / pixel, guiding is at 2.54 (I'm using an OAG) and tracking is well below 0.5 arc-seconds. For me the mount is so far below my image scale, seeing conditions, etc. it just disappears. If I move to a C11HD w/ reducer suddenly my image scale will be very close to my tracking and I will likely start to see oblong stars (at that point I would consider moving to a Astro-Physics or Paramount to guarantee the mount stays invisible, but for me that's a long ways off ;) ).

Hope this helps.

Regards,
David

#4 Startraffic

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Posted 12 November 2012 - 06:49 PM

Todd,
I have a G11 that came with the stock worm & replaced it with the OPW on the RA only. It made a HUGE difference. I will say that if you're getting 10 minute guided subs that the OPW will probably not gain you anything. If you find that the worm begins to give you trouble at a later date, change it then. Until that happens, it ain't broke, don't fix it.

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#5 tboss70

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Posted 12 November 2012 - 08:28 PM

THanks everyone. I appreciate the input.
I purchased a stock G11G2 (summer 2012) and in the beginning I did have some spikes that showed up on unguided images and wasnt sure if they could be guided out. After some gear adjusting I did get down to 10PE at the best. Avg was around 12. Not bad. The one 10 minute sub I had taken had just slightly oblong stars when viewed at 100% These were taken at 900mm FL.

Eventually I want to image at longer FLs so I know I will need to get the OPWB or the Ovision.

I'll do some more testing when my new guidescope gets here and see what i get. I was just curious if there were any new updates on the OPWB that I have not read yet.

Thanks again,






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