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Re: Ovision worm not working right


Mar 4, 2016

 


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#56987 Mar 4, 2016

�� Hello

I would like to ask for any opinion or suggestion of a problem I am having with my G11G2. slowly, I have been trying to improve the mount. So after getting nobs, and the ring spacer so I do not hit the motors with the dovetail, I decided to get the Ovision Worm.��the worm specs show about 2 arc sec peak to peak, which looks pretty good��to do AP with long focal length telescopes.��I installed��the worm and left about 1.5mm backslash. Finally, after 2 months the weather improved so I could test the mount. The problem I encounter was:

Regardless of bias balance or perfect balance, I could not get round stars even in a 60s exposure. Looking at��PHD graph and��disconnecting the guiding inputs the��RA went to 16 arc-sec in one direction and just keep going away (below the abase line). However, when��I start guiding, then��the��RA error was only 3 arc sec peak��to peak (about 20 min exposure).I��slewed to different parts of the sky (E and W) and the error did not change. I also changed the balance and��it did not make any difference. Does any body have any idea or suggestion of what could be?����Is that a sign I damaged the worm somehow when I installed?

Thank you so much

Rodrigo



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#56988 Mar 4, 2016

Hi Rodrigo,I think the Ovision worm and assembly are pre-tested by them. ...so it would be likely something else..You did not mention doing a drift alignment, or what telescope, guiding system,. image camera, or autoguide camera system you care using...The drift alignment step is critical, because even with a perfect RA drive, the errors in polar axis still have to be guided out.. So too is having either a OAG, or really strongly coupled piggyback guider system..Please give us some more details, so we can help...Best regards,

MichaelOn Mar 4, 2016 12:44 PM, "Rodrigo Roesch rodrigoroesch@... [Losmandy_users]" Losmandy_users@yahoogroups.com> wrote:

.. Hello

I would like to ask for any opinion or suggestion of a problem I am having with my G11G2. slowly, I have been trying to improve the mount. So after getting nobs, and the ring spacer so I do not hit the motors with the dovetail, I decided to get the Ovision Worm..the worm specs show about 2 arc sec peak to peak, which looks pretty good.to do AP with long focal length telescopes..I installed.the worm and left about 1.5mm backslash. Finally, after 2 months the weather improved so I could test the mount. The problem I encounter was:

Regardless of bias balance or perfect balance, I could not get round stars even in a 60s exposure. Looking at.PHD graph and.disconnecting the guiding inputs the.RA went to 16 arc-sec in one direction and just keep going away (below the abase line). However, when.I start guiding, then.the.RA error was only 3 arc sec peak.to peak (about 20 min exposure).I.slewed to different parts of the sky (E and W) and the error did not change. I also changed the balance and.it did not make any difference. Does any body have any idea or suggestion of what could be?..Is that a sign I damaged the worm somehow when I installed?

Thank you so much

Rodrigo



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#56991 Mar 4, 2016

Hi Michael

Thank you for following up with my email. The setting I used is:Image scope: Orion EON 80mm+ reducer so 400mm focal length Guiding scope: Orion 50mmGuiding Camera: Orion SSAU Image Camera Monochrome Canon Xsi

I usually use the polar scope when I use short focal length, usually I get about 2 arc-sec error with the scope.Before upgrading top Ovision I could do 2-3 min unguided with that particular scope, now I cant even do 60s. Attached is a graph from PHD over 700s. I to get the information I disconnect the guiding input so the information does not have any correction. I did not include the DEC information since it was very low.







Thank you

Rodrigo







On Friday, March 4, 2016 4:00 PM, "Michael Herman mherman346@... [Losmandy_users]" Losmandy_users@yahoogroups.com> wrote:





. Hi Rodrigo,I think the Ovision worm and assembly are pre-tested by them. ...so it would be likely something else.. You did not mention doing a drift alignment, or what telescope, guiding system,. image camera, or autoguide camera system you care using... The drift alignment step is critical, because even with a perfect RA drive, the errors in polar axis still have to be guided out.. So too is having either a OAG, or really strongly coupled piggyback guider system.. Please give us some more details, so we can help...Best regards,

Michael On Mar 4, 2016 12:44 PM, "Rodrigo Roesch rodrigoroesch@... [Losmandy_users]" Losmandy_users@yahoogroups.com> wrote:



. . Hello

I would like to ask for any opinion or suggestion of a problem I am having with my G11G2. slowly, I have been trying to improve the mount. So after getting nobs, and the ring spacer so I do not hit the motors with the dovetail, I decided to get the Ovision Worm..the worm specs show about 2 arc sec peak to peak, which looks pretty good.to do AP with long focal length telescopes..I installed.the worm and left about 1.5mm backslash. Finally, after 2 months the weather improved so I could test the mount. The problem I encounter was:

Regardless of bias balance or perfect balance, I could not get round stars even in a 60s exposure. Looking at.PHD graph and.disconnecting the guiding inputs the.RA went to 16 arc-sec in one direction and just keep going away (below the abase line). However, when.I start guiding, then.the.RA error was only 3 arc sec peak.to peak (about 20 min exposure).I.slewed to different parts of the sky (E and W) and the error did not change. I also changed the balance and.it did not make any difference. Does any body have any idea or suggestion of what could be?..Is that a sign I damaged the worm somehow when I installed?

Thank you so much

Rodrigo









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#56992 Mar 4, 2016

Hi Rodrigo,

That is good info. . .I agree that an 80 mm scope should track easily, especially with a field reducer, so something is out of alignment. .So that is a real puzzle. ..

What are the most likely possibilities?

Either (1) the RA axis has a large PE, causing stars to wiggle in 240 sec period, or (2) your polar alignment is out of position. .



The Ovision worm system would seem to rule out PE, but PE can be measured using PHD2 log file, and a free program like PECprep (here:.eq-mod.sourceforge.net/pecprep/ . ) that program is built for the Orion / Synta EQ6 / EQG, but it also has built in settings for the G11. .

Taking data through your main scope with your guide camera will tell you if your polar drift alignment is good, and also get you data for the PE measurement.. Your Gemini can also take data and create its own PEC dataset, .That will eliminate any existing PE too. ..



A few more questions are related:.

Are you doing your drift alignment through the 50mm piggy back guide scope?. If so, that may be a cause of trouble. .You really need to polar drift align using the 80mm main camera.... and ... (I think) your guide scope must be aimed at the same center of the main scope field of view, and your guide scope mechanically must be firmly locked to the main scope. .

If the guide scope axis is slightly off from the main scope axis, then a slight error in mount polar alignment will cause the autoguide camera corrections of the piggy back scope image to push the main scope image off of star alignment.. This also becomes harder to manage when the guide scope star image is smaller (wider field) than the main scope image. . .Usually you need scope rings on the piggy back scope, so you can aim it to the same optical center as the main scope. ..Easiest if you just put your main scope centered on a bright star near the meridian and equator, and then center your guide scope to the same star.. Then put your guide camera on the main scope and drift align.. Then your guiding will be on the same center.

In the end,....my experience was....

...I gave up piggy back guiding, and adopted using an OAG.. Once I got the OAG system, I got nice round stars.. I was using a piggy back 80mm guide scope on a 254mm 10 inch SCT...I could never get the coupling between those scopes to be strong enough, or not change alignment. Besides, when the 80mm scope camera would drift 2 pixels, the main camera would have drifted ~ (254/80) ~ 3X as far.. The OAG ensures that the main image is being guided directly, and the corrected star drift of a few pixels means the main image is also going to be only off a few pixels. . .(PHD says it will correct with sub-pixel movement...)

If you consider an OAG approach.......I tried several OAG units.. The one from Orion, which had lots of tiny screw adjustments, did not work for me, as the adjustments would loosen up over time (and temperature), and its prism is small, making it hard to see the guide stars.. I was able to find a used Lumicon "easy guider" that had a 2" nose and 2" back, and that has a very large prism, and that is much easier for the guide camera to focus on.. It was a headache to find the right adaptor rings, but once done... that stays as part of the main camera assembly (I have a Baader MPC coma corrector, and a 2" Nautilus filter wheel on the front of all that too so everything is really bolted together). .

The guide camera will show stars through the OAG to be fainter than through a piggy back scope, so you must then use a longer guide camera exposure, like about 3 seconds.. Sometimes, you must rotate the main camera+OAG around the target, to find a bright enough guide star.. But once you get that done, the autoguiding ensures the main camera image is well tracked...

I hope you discover your imaging trouble soon.... and are on your way to beautiful images...And I hope you tell us what the final cause of the trouble was, once you figure this out.... .

All the best,

Michael



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#56993 Mar 5, 2016

Hi Rodrigo,

there is a nice document about guiding errors here.openphdguiding.org/tutorial-analyzing-phd2-guiding-results/Maybe this might help to track your problem down.Good luckRobert.

PS: You may also ask for help (.groups.google.com/forum/?fromgroups=#!forum/open-phd-guiding) here.



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#56994 Mar 5, 2016

Rodrigo, ��At least on my computer (Windows PC) your attachment does not show up. Perhaps you can upload it to the Files section of the Yahoogroup and let us know where it is? ��With that short a focal length you should have no problem whatsoever guiding for 10s of minutes with the original or the Ovision gear. Plus that guider/imager combo is lightweight. The only thing I would worry about is flex in the mini-guider as the mounting of those is none too rigid. ��Do you have any guiding graphs with the same rig (imaging scope and guider) before you switched to the Ovision? ��Mark Christensen



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#56996 Mar 5, 2016

Hi Thank you for all the suggestions. I think, the problem is not really the guiding since I can't get an unguided picture for 60s with 400 focal length. So last nigth, I removed the motor and the gear box and tried to rotate the worm with my fingers, (clotches untigthed) what I found was it needed more effort to rotate a quarter of a turn then became soft and then hard again, like getting up and down in a roller coaster. So I went ahead and added a bit more space betwen the worm and the ring but to the expenses of increasing backslash. Now the worm rotates easly when I move it with my fingers. What I don't understand is I followed the Ovision instructions and I left 1.5 mm backslash and this time I had to increase to 2mm to have the worm rotating smooth. Do you think that this could cause bad tracking? Now I need to wait for clear night to test

Thank youRodrigo







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#57621 Jul 6, 2016

Rodrigo,

did you get your issues solved?

Hamza



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#57622 Jul 6, 2016

Odd I had to decrease the worm position; making it tighter to get better unguided performance. I actually thought I was getting to much play at 1.5mm thus went to 1.0 mm or so and was doing unguided for 5 minute exposures at 560mm.



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