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KyleStoke

PHD2 Calibration

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Can anyone tell me what would cause this strange looking calibration graph in the RA axis specifically east direction

 

Capture.PNG

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As far as I understand, bad alignment. Did you check your polar align error in guide stats?

Try drift aligning in phd2 if you haven't already, doesn't take too long and usually sorts these things out.

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Hi Jez

This is from the other night i was just looking at the log.

It was aligned using a polemaster, and it and PHD drift align don't seem to agree.

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I'd go along with this suggestion,  pa must be quite a way off....unless....you have severe Flexure of the guide scope. Which can happen with the heavier guide scopes.

 

Ray

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Hi Ray

Its a finder guider, I wouldn't rule out flexure though they are not super secure in the shoe

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46 minutes ago, KyleStoke said:

Hi Jez

This is from the other night i was just looking at the log.

It was aligned using a polemaster, and it and PHD drift align don't seem to agree.

 

I've used things like polemaster and alignmaster to align and always find alignment error in PHD - they never seem to agree. Now I only use PHD to drift align, which makes sense as this is the system which is key to your guiding. So my suggestion would be to basically not trust other alignment programs, and use PHD exclusively to align.

I don't think your problem is flex, your calibration only takes a few minutes and you won't see a huge amount of flexure in this time, it only really comes in to account over longer periods of time. That said, no harm is screwing and locking everything down anyway, as it' will ultimately affect your images.

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I did formally drift align but got fed up with the faff, I feel the Polemaster gives me good enough alignment but that there is another technical issue that pops up from time to time, like flexure or a dogy mount or setting 

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1 hour ago, KyleStoke said:

Just to add to the confusion this is the log from the day before

Capture.PNG

The log says that the calibration was done at 80 degrees declination! You need to do it within 30 degrees of the celestial equator.

Calibration that near to the celestial pole is almost certain to end in failure ;) 

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11 hours ago, Pompey Monkey said:

The log says that the calibration was done at 80 degrees declination! You need to do it within 30 degrees of the celestial equator.

Calibration that near to the celestial pole is almost certain to end in failure ;) 

Hi if you do the drift align in PHD it wants you to go to specific areas of the sky to do it, but i was always under the impression that you calibrated on a star in the area of your target, is that not correct?

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One point from me; you only have 5 calibration points in RA.  It is advisable to have at least 15 or so.  This could be explained by your choice of calibration star position near the celestial pole. 

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Hi Chris its is DEC that only has 5 but maybe this is having an effect on the overall calibration

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1 hour ago, KyleStoke said:

Hi if you do the drift align in PHD it wants you to go to specific areas of the sky to do it, but i was always under the impression that you calibrated on a star in the area of your target, is that not correct?

" You may also see a calibration failure if you're using a star too close to the celestial pole.  In those locations, fixed-length movements in right ascension often move the star only a very small distance.  In that case, move to a star location closer to the equator, ideally somewhere in the range of -30 to +30 degrees declination, and re-run the calibration. "

From here: PHD2 Manual: Calibration page

Couple that with some error from backlash, and all kinds of strange might happen ;)

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1 hour ago, KyleStoke said:

calibrated on a star in the area of your target, is that not correct?

Hi. I believe that that's only necessary if you are guiding st4. I think the OP is guiding pulse, not on-camera (?).

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The best place to calibrate is Dec zero, just east of the meridian....you need to set up the phd2 parameters to give you 12 to 15 moves west and the same north,     East moves and South moves are not part of the calibration process, they are just returning the star to the star position.

if yo get a good calibration at Dec zero or thereabouts, you don't need another one, I use mine I did several months ago irrespective of  my target position, phd2,compensates for declination changes if the calibration is good.

Ray

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