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Re: [Losmandy_users] Re: PEC Review, AO-8, New Camera


Mar 30, 2015

 


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#55500 Mar 30, 2015

Hello everyone,

New to the group but have been lurking for years.�� I have owned my G-11 for over a decade.�� I have imaged on and off with a ST-8XE and still do so until I can afford a new camera.�� I also use Maxim DL 6.�� Everthing including my cheap RC 10" is in a permanent observatory.�� I did not have time to image for a few years and am now in a position to spend more time on the hobby.�� So I am back at it.

Today's questions are associated with my Periodic Error. and the potential need to upgrade or keep my AO-8 as I contemplate a new camera.

1. I just realized that most people are quoting their periodic error as an unguided error.�� Please confirm.��

2. Maxim DL shows the graphs for the PE as it guides, but I don't see the functionality to record it unguided.�� I guess that is why people purchase products like Pempro and the like.�� Is this correct?

I measured my PE guided last night for the first time in years and found that I am within 2 arc seconds total from peak to peak.�� I used the Maxim DL functionality for this measurement.�� I believe all the telescope information is accurately depicted in the software.�� To be clear the error is within one arc sec of the base line.�� Y error is less because of my polar alignment,�� which is fair but it is��not too far off of the x error.

3. In comparison to the other member's units, is this about average, poor,��or good?�� I have yet to measure the native non-guided PE and will probably endeavor to do so.�� However, in a way it does not matter if I can guide it out.

4. If my typical seeing in South Florida is about 3 arc seconds, is not the seeing value driving the size of the stars?�� My camera pixel size is well suited for my un-binned exposures according to every chart I see.�� If I can guide down to less than one arc sec, then my guiding should produce good images, correct?�� Part of the reason I am asking is that I am trying to determine what is guiding error and what is coma or other optical effects.�� Yes I know that the edges would show the coma but I am still trying to eliminate the scope mount.

Part of the deliberations are associated with the use of my new used AO-8.�� I have developed a particular fondness to this contraption because it seems to work.�� The error I have seems to be peaky and I think the AO-8 soothes it out and produces a better image. This is important because my next camera may or may not have compatibility with the AO-8 depending on verification of all of the above and the fact that I think it really matters.

I am also contemplating fine tuning the mount again with the new worms or worm drive unit, but I think I may not need to and don't want to fix things that are not broken.

Finally, after years of working with this mount, I would probably NOT buy the Losmandy G-11 with the Gemini Gemini Go to again.�� That is because I would go for the Titan instead.�� This is a compliment to the��folks at Losmandy and Holywood General Machining.��

I did some searching through the archives and you all probably know how hard at times it is to find the search string you are looking for.

Thanks in advance for��any reply.��



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#55501 Mar 30, 2015

Let me answer some of your questions, and perhaps others can chime in with additional answers.



1. Yes, mount PE is always measured unguided.

2. You can easily turn off guiding corrections in MaxIm DL guider set up, or, simply unplug the guider cable from Gemini while letting MaxIm collect error information.

3. Your peak-to-peak guided error is hard to interpret since it's guided, but also because the error accumulates over time. If your error is constantly +/-1 arc second, that's not good. If it's +/-1 once or twice during a 10 minute exposure, you will not notice it.

4. How did you measure your seeing? 3 arcseconds is about average. With a 10" RC, I would expect much better results on a night of good seeing. 1-2 arcseconds should be doable. Again, the guiding error of +/-1 arcsecond can be significant if this happens all the time, and can be negligible if it happens quickly, and only once in a while.

AO-8 will almost always outperform a simple guider at longer focal lengths, since it can correct frequently and precisely, often many times per second.

Regards,

�� -Paul



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#55516 Apr 2, 2015

Thanks Paul for the input.�� I have committed to change out my older stainless steel worms to the newer brass precision worms to try and improve my situation.�� I need a good reference web page on how to do this.�� The worms are on their way.�� I ultimately will go to the worm block but wanted to try this first.

1.and 2.) Thanks that is what I thought I had to purchase pempro but I will try to turn off the guiding corrections and look at the graph.�� This should show the non guided peaks.�� Thanks again.3.) I have intermittent but not constant peak to trough error.�� It does occur more than once or twice in 10 minutes guided so I can see the error in my images.4.) I��measured the seeing via looking at the focus max�� FWHM target, which I believe is always around 2.9 to 3.5 or so.�� I can't seem to get any smaller values that that.

I am having trouble collimating the RC because of flexure in the cheaper than scope focuser.��I belive that flexure in the focuser is introducing collimation issues.�� I collimate utilizing Howie��Glatter lazer and it is spot on, but when I load up the focuser with all the stuff it always seems to be off.�� I have the collimator attachment on the focuser and collimate it and the secondary mirror but can't seem to get both to stay when I load the focuser.�� Maybe this is creating a problem with the seeing measurements?��

I have tried to abandon the guider port and use the telescope main port for guiding with my ST8XE but the scope does not respond.�� Is the Gemini Losmandy combination not able to pulse guide with the main telescope connection?�� Am I missing a setting.�� I am using the ASCOM drivers and Gemini APS with the POTH hub.�� I am just looking to eliminate another cable connection.�� I have the camera set to NOT USE THE GUIDER RELAY and use the Telescope connection but the telescope does not respond.

Any typical values for TVC?�� I have adjusted it��so that the response in��DEC is about equal when direction is changed relative to the amount��of time I press the button.����The values of 50-80 seem to be correct.�� Any other suggested values or how to set this?

Sorry it took me so long to respond.�� I got a message that I was rejected from the group application.�� Glad to see I am in.



Thanks in advance for any response.����

---In Losmandy_users@yahoogroups.com, yh@...> wrote :

Let me answer some of your questions, and perhaps others can chime in with additional answers.



1. Yes, mount PE is always measured unguided.

2. You can easily turn off guiding corrections in MaxIm DL guider set up, or, simply unplug the guider cable from Gemini while letting MaxIm collect error information.

3. Your peak-to-peak guided error is hard to interpret since it's guided, but also because the error accumulates over time. If your error is constantly +/-1 arc second, that's not good. If it's +/-1 once or twice during a 10 minute exposure, you will not notice it.

4. How did you measure your seeing? 3 arcseconds is about average. With a 10" RC, I would expect much better results on a night of good seeing. 1-2 arcseconds should be doable. Again, the guiding error of +/-1 arcsecond can be significant if this happens all the time, and can be negligible if it happens quickly, and only once in a while.

AO-8 will almost always outperform a simple guider at longer focal lengths, since it can correct frequently and precisely, often many times per second.

Regards,

�� -Paul







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#55517 Apr 2, 2015

The AO-8 is great, but only with the bright guide stars.�� Once you get beyond 0.75 sec exposure times it is not as good and only takes out the most onerous peaks and valleys.....I think.



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#55518 Apr 2, 2015

Sorry, but what's your name?

You should measure the unguided performance of your system, first. You may not need a new worm if your periodic error is low and smooth. That's the main reason to measure unguided PE, so that you have an idea of what error you really need to correct.

Sag in the focuser or poor collimation can easily distort stars and cause higher FWHM reading. You should figure out a way to fix this, as it'll cause problems while imaging.

Pulse guiding is fully supported by the Gemini.NET ASCOM driver. I don't know why you are using POTH, but in most cases, you don't need it since Gemini.NET acts as a hub already. You can connect as many apps directly to Gemini.NET as you want.

I prefer to set TVC to zero, as the backlash can vary at different locations in the sky (and on the worm-gear) and in some cases, TVC can undershoot, and in others -- overshoot the desired position. Just unbalance the mount slightly so that the gear teeth are not floating freely between worm flutes.

Regards,

�� �� -Paul



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#55519 Apr 2, 2015

Unless you go to a separate guide scope to get brighter guide stars, you'll find that the AO is still always better than guiding using mount corrections. Think about how much weight the mount must move in order to make the tiny guide corrections (all your equipment + counterweights)!��

In comparison, all the AO-8 must move is an extremely light weight refracting element, barely a few grams.

What's more, if you are having issues holding collimation and/or issues with focuser sag, the external guide scope will not work well in your set up due to differential flexure.

Regards,

�� �� ��-Paul



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#55531 Apr 3, 2015

I changed the driver to the ASCOM Gemini.net driver and it is great.�� The pulse tracking worked fine.�� Glad to see another cable gone from the setup.

I measured the PE using Pempro and Maxim DL and got two different values.�� Pempro showed RMS Error of 5.647 and periodic error of 12.5/-9.8.�� So that is a swing of 22.3 arc seconds!�� I really like pempro.�� Very different than a decade ago.�� Seems like everything is much more stable with all software.

Y swings from .4/-.4 and RMS of 0.430�� That sounds about right and validates the Pempro measurements.

Maxim shows something different and I don't know why.�� The tracking error graph shows peak to trough of about five (5) arc seconds.�� Don't know what is going on, but will check the settings.�� Maybe the image scale is incorrect on the pixels as calculated by the software using the telescope information.�� I got a screen shot of the plots but don't know how to post.

Brass worms come in today, and I think I��am going to replace the stainless ones.�� I made a mistake and purchased two.�� Hopefully Losmandy will take back one of them.

Thanks for all the help.�� Getting the pulse��guide to work through the telescope connection and turning me on to the Gemini.net driver was great.��



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#55532 Apr 3, 2015

Hi Emilio,Measuring the PE was successful...great. ..you now know your baseline.But getting to low PE with just the brass worm replacement may not get you to the optimal PE...Please look for Web articles on getting the two worm blocks aligned.. That seems to be a common problem...David Partridge of our group recently got very low PE by also replacing his worm bearings with higher quality ones...I suggest you contact him directly for advice..Losmandy sells a product called the OPW one piece worm block, that improves worm block alignment... Please look into that too (I think David kept his 2 piece blocks, successfully getting low PE)..Lastly, I have read of some. variation in the quality of the brass worms themselves.. You might just hang on to both worms and see if one surpasses the other...if the first one does not meet your PE goals.All the best,

MichaelOn Apr 3, 2015 8:38 AM, "bigeastro@... [Losmandy_users]" Losmandy_users@yahoogroups.com> wrote:

.I changed the driver to the ASCOM Gemini.net driver and it is great.. The pulse tracking worked fine.. Glad to see another cable gone from the setup.

I measured the PE using Pempro and Maxim DL and got two different values.. Pempro showed RMS Error of 5.647 and periodic error of 12.5/-9.8.. So that is a swing of 22.3 arc seconds!. I really like pempro.. Very different than a decade ago.. Seems like everything is much more stable with all software.

Y swings from .4/-.4 and RMS of 0.430. That sounds about right and validates the Pempro measurements.

Maxim shows something different and I don't know why.. The tracking error graph shows peak to trough of about five (5) arc seconds.. Don't know what is going on, but will check the settings.. Maybe the image scale is incorrect on the pixels as calculated by the software using the telescope information.. I got a screen shot of the plots but don't know how to post.

Brass worms come in today, and I think I.am going to replace the stainless ones.. I made a mistake and purchased two.. Hopefully Losmandy will take back one of them.

Thanks for all the help.. Getting the pulse.guide to work through the telescope connection and turning me on to the Gemini.net driver was great..



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#55537 Apr 3, 2015

I replacedmy steel worm with the brass worm and the improvement was quite dramatic. I wasunable to remove the bearings from the old steel worm so I suggest you get newbearings. The installation is simple. First remove the motor and gearbox andthen the worm blocks and worm.

To adjust the Backlash:You adjust one worm block at the time. First the blocknearest the motor .This bearing block only rotates! Use a feeler gauge to makethis parallel to the flats on the mount by filling up the gap space with thegauge thickness blades . Leave the filler gage in to keep it perpendicular andparallel with the flats on the mount while you tighten the bearing block��bolt. You want to keep the center line of the blocks bearing as much in linewith the worms center line�� as possible. This block only rotates it doesnot move up or down or side to side. You are done with this side.

Next,,on the other side (this is where the worm adjustment is done!): and whileapplying an in word pressure and (towards the other bearing block, motor side)and while pressing bearing block upwards to the feeler gauge and flats of themount(this keeps the block parallel and in line with the worm whiletightening),and with the same feeler gauge thickness as before, tighten theother block. Do this with just the bare mount, no weights, weight shaft ortelescope. If you cannot easily turn the worm with your fingers, increase thegap.

Goodluck







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#55542 Apr 3, 2015

Thanks to all that posted.��

Michael,

I am keeping both worms.

I know about the unified worm/mount unit but they are on back order and won't have them for 8 weeks.�� As a result I am going to replace the worm anyways for now and see what happens.�� Heading to the auto parts store for measuring device for the gap.

Hope I don't have to change the bearings but if that comes to pass ok.�� Will have to live with the steel worms since I have a run of clear skies, although with bright moon here in Marco Island, Florida.

Thanks again for the help.



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