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RA peak on the PHD graph - Why?

swag72

By swag72
in Imaging - Discussion

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swag72

swag72

Posted
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Last night I was set up and guiding and doing 15 min subs on some Ha data. I noticed a big RA peak on my PHD graph. As it turns out, none of my subs were useable, all had some tracking issue - I wonder if it was this - That the RA would peak every so often as it did in this graph.

So, what would be causing this? Why would everything be ticking along nicely, then totally out of the blue I get a massive RA peak? I have squashed the graph down so that you can see the full extent of the peak. Perhaps I need to do some guiding and watch like a hawk to try to see if it is a regular pattern?

post-18339-133877636487_thumb.jpg

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swag72

swag72

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Not that I am aware of - Just firing up the astro PC to see what settings I have on PHD - Is it just a case of the 'log files' being checked?

**Edit** Yes I do have the log files checked in the tools menu in PHD _ how do I check the log then and once the computer has been switched off are they saved?

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Psychobilly

Psychobilly

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You should be able to.. I have uses Pecprep in the past...?

form the user guide...

PECPrep can analyse PE data captured by several popular capture and guiding applications:

perecorder (Specially written for close integration with EQASCOM)

Stark Labs PHD

K3CCDTools

MaxImDl

Guidemaster

Metaguide

CCDTools

AstroArt

If your an excel jockey then you can import the logfile (.CSV) and graph the results...

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swag72

swag72

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I can't find a saved PHD log file. I will have to go out tonight and sit with it and hope I can see where to save to and then analyse it.

Do I have to do anything special in PHD to save the log? I ask as I am always asleep when the computer and PHD switch off, so never see the end of a session!!

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jgs001

jgs001

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Mine did that on a run once... I lost the first two subs to it... I still have no clue what caused it, but I stopped guiding, restarted PHD, started guiding again, and it didn't happen after that. My guess is something didn't quite happen right in calibration, but as I say, that's just a wild guess.

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swag72

swag72

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Is it a lump of crud on the RA worm? Does the spike repeat at worm cycle intervals?

Dennis

I don't know Dennis - I'll be running through tonight and keep the log. None of my subs were useable last night all ruined, so perhaps it is on a cycle - I hope I will know tonight - So standby!!

John, I have noticed that this does happen quite often with my mount on the RA axis. I hope I will be able to go some way to getting it diagnosed tonight.

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James

James

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I had a similar problem not that long ago which I ended up narrowing down to my counterweight shaft on my EQ6 being fully extended but not clamped tightly. I can only guess that as the mount rotated the shaft was jerking slightly (the shaft is very very slightly bent).

Unlikely but you never know :BangHead:

James

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chrisshillito

chrisshillito

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I can't find a saved PHD log file. I will have to go out tonight and sit with it and hope I can see where to save to and then analyse it.

Do I have to do anything special in PHD to save the log?

Well you have to tell PHD to take the log in the first place - have you checked the "log info" checkbox? If logging PHD will display (log active) in its window caption. The logfile will be dumped into "My Documents".

You can load PHD logfiles with PECPrep if you want to anaylse the guiding performance or identify periodic motion that the guider is unable to remove.

Chris.

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swag72

swag72

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Ticking along nicely, and so far I've had two peaks and one trough in RA - Nothing to explain why and so far I can't put any time on them. Will let it run for about an hour then will export the file PECprep and hope that someone can understand what's going on!!

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chrisshillito

chrisshillito

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Sorry Chris, where do I get that info from? I'm using a 9x50 finderscope and a QHY5, not sure I'd even know what star I am guiding on.

Its not too critical - to the nearest degree is good enough. Where roughly is your mount pointing (any nearby bright star?)

The PECPrep import needs to know declination, focal length (of the guidescope) and pixel size of the camera if it is to display the data in terms or arcseconds of movement. If you don't know that info don't worry, we can still analyse your spikes and see if they are periodic.

Chris.

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swag72

swag72

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I'm imaging NGC6960 at the moment, so my bright star is 52cyg.

The camera is a 1000D DSLR, what is the focal length of a 9x50 finderscope?

I can then run it through PECPrep in the morning with the right info.

Thanks Chris, much appreciated.

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chrisshillito

chrisshillito

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OK, so on the pecprep phd import form you will enter the following

Data to Load: RA Error (you may also want to look a declination later)

Focal Length: 200 (9x50 finderscopes are typically around 200mm)

Barlow/Reducer factor: 1

Pixel Size: x=5.2, y=5.2 (this is the guidecam pixel size)

Binning: 1x1

Compensate for DEC: checked

declination = 30.75

Chris.

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swag72

swag72

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Thanks for these figures Chris - Once I have loaded the figures into PECPrep is there any way I can change them? I ask as I was playing around last night without these figures and that is now the only data I have, but it is of course with incorrect figures.

If I go into the text file and change the number I can, ie Focal length, pixel size, declination and make compensate dec = True - Will that work?

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