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Author Topic: PEC  (Read 6532 times)

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Offline mcrossley

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Re: PEC
« Reply #15 on: 13:31:23, 17 October, 2006 »
Back to Dave's original premise about modelling the error over the whole wheel. Isn't that what ProTrack on the Paramount ME does?  I'm not that familar with it, but after building a good model (200 stars anyone) and training the PEC (worm errors only), I believe they claim you can then take longish exposures (15 minutes) without using an autoguider?

Normally we try to avoid 'fast' changes in RA using PEC for high resolution imaging.  But for wide field images, the a well behaved worm PE is too small to be of concern.  However a slow, larger amplitude change in RA would be of concern.  Modelling this out would mean no longer requiring to guide wide field shots either.

Hmm, that's flogged this the death methinks.
Mark
C14 SCT + Hyperstar » SV4 Apo » MI-250 + Gemini » QHY8 » QHY5 » ToUcam
http://www.wilmslowastro.com/

roundycat

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Re: PEC
« Reply #16 on: 15:33:19, 23 November, 2006 »
Dave

PEC is not the only consideration. If your polar alignment is off it doesn't matter how good your PEC is, guiding will be essential

Dennis Isaacs

michaelmorris

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Re: PEC
« Reply #17 on: 22:21:27, 25 November, 2006 »
I'm pretty new to the LX200 range.  I've recently purchased an 8" LX200 Classic and I want to PEC train it.  I'm also interested in autoguiding my digital imaging sessions and have recently discovered PHD guiding software.  Having read up on it, it strikes me that PEC training is going could be be an awfully tedious business.

So here's my question.  Can I use PHD guiding software, or other autoguiding software, to run my PEC sessions?  I one can, it strikes me that is going to be much easier and more accurate than manual guiding during PEC training.

Offline coatesg

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  • Graeme Coates
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Re: PEC
« Reply #18 on: 16:35:10, 29 November, 2006 »
So here's my question.  Can I use PHD guiding software, or other autoguiding software, to run my PEC sessions?  I one can, it strikes me that is going to be much easier and more accurate than manual guiding during PEC training.

Yes - but many pros and cons here. By using an autoguider, you can add in errors based on both the imager chasing the seeing, and also "lag" errors based on the time difference between the actual error, the camera exposure and the time it takes for the correction to be fed back.

You could use the averaging function to try to smooth the errors out I guess, and on a bright star the lag time won't be too large I shouldn't think. Humans tend to be better and distinguishing between seeing and error, but their reaction times are probably even slower!

Of course the advantages are that you're not there playing ping-pong for ages! I never tried it this way myself when I owned an LX200 (though I did use a webcam to display the image onto crosshairs on screen, and then manually correct the errors). I'd certainly have a go, though it may not be exactly accurate, but hopefully an improvement. You only need to bring the error down to managable proportions - the autoguider should do the rest of the work if you can't get it any better.

(I believe PemPro could be used, but you'd need to replay the PEC corrections to the mount rather than doing a direct upload. Though this does cost, and it may depend on what camera you have, software, etc and may not be practical. I have heard that some people have been successfull that way though).

Cheers,

GC
Graeme Coates
http://www.chromosphere.co.uk
Titan + Gemini L4v1.04 :: 14" f4.6 Newt :: WO FLT110 :: FC-60NZ :: ST2000XM + CFW8 :: DMK 41AF02.AS

Offline John Winfield

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Re: PEC
« Reply #19 on: 19:35:20, 03 December, 2006 »
Isn't that what ProTrack on the Paramount ME does?  I'm not that familar with it, but after building a good model (200 stars anyone) and training the PEC (worm errors only), I believe they claim you can then take longish exposures (15 minutes) without using an autoguider?

I found out about ProTrack just a couple of weeks ago and have written a generic version of it using ASCOM which uses the MaxPoint mount modelling s/w to drive the corrections. This will therefore correct for things like atmospheric refraction, polar misalignment, mount flexure etc

It seems to work pretty well for me and I've released it to a few volunteers for beta testing right now (if their skies ever clear).

MaxPoint isn't free, but my s/w will be, so if you have MaxPoint already you can try it for yourself.

Cheers,

John
10" LX200R, Pentax SDHF-75 on AP900
ART11002 + TT Filter wheel, DSI Pro.
WO ZS66SD + PST.
Old kit:
C11 on EQ6 mount. Meade SN8 on LXD75 mount, ART285

davemahoney

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Re: PEC
« Reply #20 on: 21:03:15, 05 January, 2007 »
I am out of my depth with this topic.
It sounds to me that the drives offered by manufactures do not have an anti backlash gear. (All accurate lathes and mills come with backlash equiped as standard).
This is a drive where all aspects of the involute curvature of the worm and driven gear are always meshed to create a solid union of the mechanical componments.
Dave.

Offline John Winfield

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Re: PEC
« Reply #21 on: 22:21:08, 05 January, 2007 »
Dave,

I don't think backlash is really much of an issue for imaging, it's more the non-linear drive rates from imperfectly figured gears which cause the issues.
10" LX200R, Pentax SDHF-75 on AP900
ART11002 + TT Filter wheel, DSI Pro.
WO ZS66SD + PST.
Old kit:
C11 on EQ6 mount. Meade SN8 on LXD75 mount, ART285

Offline coatesg

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  • Graeme Coates
    • Chromosphere
Re: PEC
« Reply #22 on: 22:55:16, 05 January, 2007 »
John is entirely correct here - the RA drive of a mount should never have to reverse when imaging (assuming you are guiding at siderial speed or less) so backlash isn't a problem when you have the mount slightly balanced towards the east as it's always driving.

One rotation of a worm (the period) has a lot of error which should be periodic and can (should) be largely corrected by PEC (though you can have errors that occur over a different period (eg the infamous "76 second errors" of the Losmandy mounts) which can't be corrected by PEC...  :-\ )

GC
Graeme Coates
http://www.chromosphere.co.uk
Titan + Gemini L4v1.04 :: 14" f4.6 Newt :: WO FLT110 :: FC-60NZ :: ST2000XM + CFW8 :: DMK 41AF02.AS

 

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