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Re: How to train PEC
Comments... 1. You don't need any PC connection, per se, to run the Gemini PEC recorder.? You could use an autoguider camera and the ST4 port to do it I suppose. 2. If you are looking at PHD2 on your PC,? and you can use its Manual guide to move your mount (remember Gemini must be set to Guide mode or easiest to select "G" on the Gemini.net applet) then your mount is getting pulse commands from the Ascom system. (You had to install ASCOM first and the Gemini.net driver).?? In that Gemini.net driver, I think is how you either select the Serial port, or ethernet connection method. Anyway... play around and you will find a way. ...! Have fun, Michael? On Nov 26, 2017 8:26 AM, "yh@... [Losmandy_users]" <Losmandy_users@...> wrote:
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Re: How to train PEC
>?I think the big question is what is PEC for? It is my view that it is there to get you better unguided exposures.
I know this is a frequent subject for debates, but proper PEC programming does help prevent tracking errors before they happen. This results in better guided or unguided performance. An autoguider can only correct errors after they have occurred, PEC can correct them so they never happen. If you want to compare PEC to PPEC, there may still be benefits, although these may be fewer
PPEC is a great tool, but generally it's not better than PEC for both, guided or unguided exposures. In fact, PHD2 team recommends to train PEC before using PPEC if your mount allows it. Perhaps that's the best of both worlds: PEC correcting most of the errors, and PPEC picking up any small uncorrected errors that remain. Regards, ? ? -Paul |
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Re: How to train PEC
Magnus, You are correct : you can use your autoguider with the Gemini's built in PEC recorder /corrector.? You skip using the old hand controller method.? The correction signals from the autoguider work just fine. That is not clearly explained in the Gemini 1 manual.?? You want to start by a precise polar drift align,? using a star near meridian and the celestial equator. That is important because the PEC you want to correct is the RA's error, and even though the software says it can subtract out DEC drift, you want that as near zero as possible. After drift alignment is clean and DEC drift is near zero over 8+ minutes, test that your autoguider is working correctly.? Remember to put the Gemini.net into G for Guide mode, else the Gemini will not accept any autoguide signals. Take a 10 minute? autoguide image.? ?Are the stars correctly round...no glitches?? If the stars are proper and no glitches, you can start a PEC recording. Again select a new star near meridian and equator, perhaps point the scope to the west, then slew to a star just east of the meridian that will pass to through meridian over time.? You do that because you want to run about 3 PEC recordings and "add" and "average" them in the Gemini system. The first PEC recoding will last exactly 8 minutes. Before that begins, the Gemini will transfer it's existing PEC data to its SRAM backup register, but that is all 0s. ? ?The system knows from its optical encoder where the starting position is (relatively, not exactly).? When the first run ends, the Gemini puts that data into its primary PEC register (in SRAM).?? When you start the next run, the Gemini will first transfer it's PEC data to the SRAM, then wait for the worm to get back to its same starting rotation.? That could take up to 7.99 more minutes.? Then the run itself will take 8 minutes.? At the end of that ND run, the 2nd PEC data is in the "top" PEC register.? You can tell the Gemini to "average" the 2nd run with the backup data.? That averaged data is now in the topmost PEC register in SRAM.?? You should use Gemini.net to save that data into your PC in a file.?? You can redo the steps of the 2nd run.? It is not clear to me how averaging the 3rd run works.? It might actually have (in another register) a counter so it knows this is the 3rd run, so all 3 runs are equally weighted.? ?Or it may be just takes 1/2 of run 3 and adds it to 1/2 of (the PEC backup data).? Only the person with the source code can say for sure.?? There are commands to smooth the PEC data, and other things.? I used those commands also.?? Save the resulting PEC to your PC in a new filename.? When you are done, test the PEC by taking a 10 minute image.? If you had a glitch you PEC data will have recorded the glitch and your PEC image could be worse than one plain autoguided.? If the PEC has a glitch, you can upload one of the earlier PEC files to the Gemini and see if it is correct.?? And: You must park your mount before shutting off power.? That puts the worm in a known (in SRAM) rotation.? (It is said that even if the power goes out, the Gemini knows the last worm position, but on other mounts like the Atlas, you must always park.) On power up, the Gemini always defaults to "PEC OFF".? Be sure to turn that on in the hand controller.? There is a checkbox in Gemini.net to automatically turn on PEC when it connects.? You could ensure your PEC is on using that.?? Epilogue: PEC did work well for me, but I no longer use the PEC...I was lucky to get my PE without PEC down to ~1arcsec, so regular autoguiding gives me round stars.? Thats,all written up in the PDF "Improving the PE of the G11" in our group files section.?? (I will send you some Belleville worm washers,? Magnus.) All the best, and hope these comments help you. Michael? On Nov 26, 2017 6:08 AM, "jfev5mnsvqiyzpq756wvokt55jve7sbg2esr5mip@... [Losmandy_users]" <Losmandy_users@...> wrote:
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Re: How to train PEC
I think the big question is what is PEC for? It is my view that it is there to get you better unguided exposures.
I believe that if you taking guided exposures, then you don¡¯t need PEC (at least not traditional PEC) but just rely on PHD2 (with possible use of PPEC). I¡¯ve never heard of anyone actually doing a proper double blind test to see which is the better approach. And in answer to your question about using guiding s/w to train PEC, yes that¡¯s what I do: Set up PHD2 with the guide camera in the imaging scope, calibrate it and start guiding. The start the PEC training. Dave From: Losmandy_users@... [mailto:Losmandy_users@...] Sent: 26 November 2017 14:09 To: Losmandy_users@... Subject: [Losmandy_users] How to train PEC Hi! I'm trying to get my head around how I can train PEC in a good way. I understand that I can do it manually, that is with an eyepiece and manually issuing guide commands. But: If I can do that manually, could I not use PHD2 to do the same? Use the RA guide commands to train PEC, instead of me sitting there trying to guide? That is: manually engaging the "Train PEC", then start the gudiing only in RA, and let it run. Take a number of runs, then average and smooth them. Would that work? Thirdly, Pecprep seems to be a utility that can produce a "PEC file". Can I use that and someway upload to the Gemini 1? I understand Pecprep to be part of th EQMOD project, and that does not include Gemini, but is it doable anyway? Finally, I can use Pempro. However, somewhat costly.... is that worth the money? Magnus |
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Re: G11 Guding PHD2 rms number High G1
aha! I'd like to look at your PE for clues. Please send me the unguided PHD2 logfile, with info on your Scope FL aperture, and Autoguide camera pixel size X and Y, and any Barlow info (same data PECPREP asks for...).? I'm at mherman346@.... Certainly if your mount is new, under warranty, and not satisfactory, get Losmandy involved.? I only have the oldest CG11 example,? and a modern but not newest GM8.?? Best, Michael? On Nov 25, 2017 12:27 PM, "gvblk4@... [Losmandy_users]" <Losmandy_users@...> wrote:
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Re: Help with DEC backlash/jumpy guiding
Hi Magnus, When you moved to another object, or did a meridian flip, the problem went away or got better.?? So I consider 2 possible causes.? One is the DEC of the mount, and the second is the guide scope/guide camera.?? If you are using an OAG, that will solve the 2nd problem and I only guide that way.? Any slight change in the guide camera or guide? scope position will glitch your autoguiding, and due to the weight of the autoguide camera cable, that force changes with RA/time, and with meridian flip.?? Or, as you mentioned, it could be the mount DEC axis too...as you said a possible? cause of the trouble in your last description.??That is: I think you must have a slight DEC axis physical hysteresis in the worm mounting.?? When you moved to another object, or did a meridian flip, the problem went away or got better.?? If you think about it, in a perfectly polar aligned system, the RA worm is constantly moving toward positive RA, which may keep a force on one worm bearing.? But the DEC worm should not be moving (ignoring refraction of the air, and seeing).? The DEC axis can wiggle.? And PHD will have a time lag or overshoot trying to compensate for that DEC hysteresis.? ? If you have a slight I mis-balance in DEC, its ring gear will be pulled against its worm gear, pressing the worm either left or right against one of the worm bearings...the other worm bearing is more loose.? Over the night, or pointing to other objects, that misbalance changes net force on the DEC worm.? The net force will be a function of the RA angle and DEC axis angles.? (The force on the RA worm is a function of the RA angle and the polar axis angle, but not the DEC angle.)?? Bottom line, in the Losmandy original design, the DEC worm is not kept in a condition of constant constraint during the night of imaging...even if you had a hanging weight wrapped on it.? Note that the highly rated Ovision worm system designed in a Belleville washer for this purpose...Losmandy did not.?? As the night temperatures change, the brass or stainless steel worm is going to expand or contract differently than the aluminum holding the worm blocks, and the aluminum worm blocks themselves. So if the system compressing the worm bearings was "tight" at one time/ temperature, it can become loose at another time/ temperature.?? Hysteresis might be curable in PHD2, and it might be tolerable with a wide angle, short FL scope image.? But if you are using a long FL scope like an SCT, it probably is worth trying to fix the hysteresis mechanically. You mention the possible benefit of a Belleville washer and that you have not found these.? I have a stock of them for the Losmandy worm bearings (and the Orion Synta Atlas too...same problem).?? Since they are flat, they easily mail from US to international destinations in a letter.? For?$5,?I can send you 3 of them, and you have 1 for RA, one for DEC, and one spare (though they never should break).?? You will find installation instructions in our Files section under my name.?? Some simple hand polishing is required with very fine sandpaper or emery cloth to polish down the perimeter of the far worm bearing, so it can slide in its worm block cylinder.? Pulling out the rear bearing can be a challenge but I show how to form a simple puller to do that.?? You lube that cylinder and assemble the washer behind the bearing, pressing the blocks together so the spring constantly pushes the bearing on the worm. That keeps the worm in place, and keeps the Oldham coupler pieces together (which you must do or that alone will cause glitches!), and also keeps both worm bearings "compressed" so they keep lowest rumble preformance. To get the lowest RA PE about 1 arcsec native PE (no PEC), I found a benefit from replacing my worm bearings too.? I used ABEC7 rated ones, under $20?in the US.? David Partridge in the UK found great results with ABEC5 rated ones he got in Europe.? ?We both used the brass Losmandy worm, but David used original 2 worm blocks and I used an OPW.?? Wow...a lot of writing at 5AM! Hope you solve your issues...we all await your images!? Michael? On Nov 25, 2017 12:09 AM, "jfev5mnsvqiyzpq756wvokt55jve7sbg2esr5mip@... [Losmandy_users]" <Losmandy_users@...> wrote:
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Michael Herman
Paul Kanevsky
Mearl Balmer
David C. Partridge