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Originally Posted by g__day
Guys interested in your thoughts.
Tuning the PE of a well polar aligned mount I presume can greatly improve its performance before auto-guiding kicks in. In my case I have a permanent set up on a pier.
But what software and hardware do you recommend to get the best results?
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Using PEMPro is the best way. Actually, I’m going to be really brawn and brave and state it’s the only way if you are serious about reducing your mounts PE. Sure you can simply auto-guide and tell the mount to record the correction into PEC, but this is erroneous (especially if you can only store one PEC correction and not average multiple worm runs). Or you could (heaven forbid) recording it by looking through a guiding eyepiece and make the corrections manually – complete waste of time, though some form of PEC is better than none.
Quote:
Originally Posted by g__day
I have some intuitions I'd love confirmed, namely I presume it's best to:
1) run through not just one complete revolution of the gears - but maybe do 10 and average it and playback//upload the inverse of this averaged run to you mount/hand controller.
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Yes, one complete worm revolution is not sufficient. Though with modern engineering worms have become consistent, but it’s still better to record at least six worm runs. Actually, the reason why you record multiple runs is to also compensate for the seeing conditions. If we specifically look at PEMPro for example; it requests you locate a star at zenith, just west of the meridian. This reduces the amount of atmospheric turbulence. By performing multiple runs you average out the seeing to provide accurate measurements of the worm/gear.
Quote:
Originally Posted by g__day
2) guide assessing error from your main scope at its greater focal length then do so from the shorter focal length of your guide scope.
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Not certain what you mean. If I understood your question correctly, you should record PEC from the longest focal length instrument, but this depends on the arc/sec pixel combinations of the main scope and guide scope. You can assess from the PEC correction curve you’ve created from either instrument.
Quote:
Originally Posted by g__day
3) correct error directly from your software to calibrate error e.g. PEMPro rather than indirectly thru say running PHD with 1.0 second updates and watching its guide moves and hoping seeing isn't getting in the way?
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You can either get PEMPro to directly upload the PEC correction curve to the mount (if supported by the mount) or get PEMPro to playback the PEC correction curve while you manually configured the mount to record PEC. The two methods have the same result. Direct upload is easier and quicker. Don’t expect good results if you simply tell PHD to guide at 1 second intervals watching a guide star while you record the PEC. Yes, you’ll chase the seeing, this is guaranteed, but more importantly a PEC correction curve should be smooth. PEMPro does more than just record a guide stars movement due to mount worm/gear error. It has some advanced features of analyzing and building the right curve for your mount. You can manually change the curve to tweak the last little ounce of performance from your mount. This is something simply guiding with PHD and recording PEC simultaneously will not achieve.
Quote:
Originally Posted by g__day
4) ignore guding in declination - in case your slightly off SCP alignment?
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Polar alignment has nothing and I mean absolutely nothing to do with your mounts PE. Even if your polar alignment is off, your PE will remain the same. PEMPro will monitor a star for drift if polar alignment is off and will correct for it. This does not alter the analysis of your mounts PE. If you are way off alignment PEMPro will have a hard time keep things in the camera FOV, but it is still achievable. In general, yes ignore drift in DEC. Considering you’ve got a permanent set up and use Maxpoint, you should be able to get under the 30 arcsecond polar alignment error in Alt/Az.
Quote:
Originally Posted by g__day
5) use a fast and sensitive USB2 capture device your software accepts.
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Not needed. You’re not downloading full frame images every time – only to initially acquire a star to analyse. Once a star is found, sub frames are downloaded thus image download times are very quick. Typically a 50x50 pixel sub frame is sufficient. Sensitivity – umm yes. But nothing out of the ordinary. If you find stars now to guide on, then your camera is sensitivity enough. Of course a cool CCD camera will allow you do guide on higher mag stars. Typically mag 15-17 through RGB filters or mag 10-13 through narrowband Ha,OIII,SII filters. You’d only guide through a clear filter when doing the PEC analysis you high mag stars aren’t an issue. PEMPro will choose a suitable star on your behalf – generally something that is not going to saturate the well depth too quick resulting in inaccurate measurement.
Quote:
Originally Posted by g__day
On the last point I was interested in trialing PEMPro v2.0 - until the author (Ray) informed me on the weekend it will be < 3 months until it will natively support Meade DSI input. Also I am unsure whether or not you need one or more 3rd party software suites to run PEMPro or PrecisionPEC from Software Bisque? (e.g. a launch program like CCDSoft5 or Sky6 or MaxImDL etc and a video in stream processing software?). It's not well described or documented!
Any suggestions or a how to manual would be greatly appreciated. At present I just did a rough train of my mount by looking for a star near the zenith - running PHD on my Megrez 80 mm - 500mm focal length into a Meade DSI - with probably a 1-2 second guide interval and setting the Mount to remember and replay corrections! I am sure I can do better!
Many thanks folks - interested in what you advocate software and hardware wise and at least equally importantly the recommended approach or process you follow!
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Correct, native support for the Meade DSI is not available at the moment, but you can get it to work through a software package such a MaximDL or CCDSoft (if they support it). I know MaximDL supports DSI cameras. This leads me onto your next question… you’ll need either of the two packages mentioned, or AstroArt or MS DirectShow (used for web cams). PrecisionPEC is simply a rebadged version of PEMPro for specific use on the Paramount ME’s. PEMPro works on the Paramount ME’s. PEMPro is also bundled with the AP mounts (900/1200 GTO’s). You’ll also need to download .net 2.0. The beta worked with 1.1 if I recall correctly. Note: Tak mounts don’t support PEC. The worms/gear are very smooth already, however I feel certain if Tak supported PEC you could squeeze more from the mounts. After all, the Paramount ME also has a extremely low PE out of the box, but you can still rework the PEC to further reduce the PE – in some cases down to +/- 0.8 arcsecs (peak-to-peak)!!.
By all means, record your own PEC curve using PHD. Some form of PEC is generally better than nothing. Be careful that the PEC curve doesn’t work against your guider. If your guider is making more corrections after the correction, you’ll need to re-record PEC. This method works reasonably well if you mount supports multiple PEC curves like the Losmandy Gemini telescope control system. The Gemini will record multiple curves and allow the operate to combine them through an average function. This significantly improves the accuracy, but does not compare to the accuracy you’ll obtain using PEMPro.
As David indicates, PE is usually only part of the problem. Mirror shift as he highlighted can cause major problems. A good PE curve will not assist in this regard. The best way to correct for such issues (mirror shift) is on axis guiding.
You can see some of my post PEMPro results on another thread -
http://www.iceinspace.com.au/forum/s...ad.php?t=20988 The topic is the deference between an AO7 and PE, but still somewhat relevant. Unfortunately I didn't screen capture the pre-PEMPro results, but it wouldn't be hard to capture, just turn off PEC and monitor
Hope this helps.
Cheers
