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How to use AstroArt 5 for guiding?

Gina

By Gina
in Discussions - Software

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Merlin66

Merlin66

Posted
Posted

Chris et al,

AstroArt recommend that the guide camera should be within 25 degrees of the RA/Dec. (See p96/97 of the Users Guide)

I think this may be due to the "stepladder" effect of having to correct by issuing pixel x/ pixel y corrections.

In Gina's example, at 45 deg, the corrections must be almost equally applied to both x-y - I think inevitably there must be at least a slight delay between the signals which could impact on the guiding?????

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chrisshillito

chrisshillito

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In Gina's example, at 45 deg, the corrections must be almost equally applied to both x-y - I think inevitably there must be at least a slight delay between the signals which could impact on the guiding?????

If your camera is a 45 degrees and you observe a guide star movement consisting of of equal amounts of  X and Y pixels then what you have experienced is a mount movement in either the RA or the DEC axis - not both. Only a single correction would therefore be required.  From the point of view of corrections issued to the mount the camera being at an angle really makes no difference at all - you are after all correcting for the same mechanical and alignment errors, and these don't change if you twist the camera.

Whether AA supports simultaneous guide corrections I don't know (PHD does, as does the EQMOD driver).

Assuming star image is not a single pixel point, but is dispursed over a circular area of pixels then the centroid algorithm of the guider should not be unduely affected by a 45 degree orientation (rotate the star by 45 degrees and its not going to look any different!).

Given Olly's experiences it would seem however that AA is not entirely reliable in its measurement of angles and so thet best approach would certainly be to set the angle precisely yourself and tell AA what that angle is rather than have it calculate it. Clearly the easiest thing to do is always setup orthogonally. If its any consolation PHD measures the RA and DEC angles separately and doesn't seem to mind at all if they don't add up to 90 degrees!

Chris.

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ollypenrice

ollypenrice

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Another thing; AA5 gives you the option of a binning mode called Hires fast (which initially baffled me because what was I hiring??) but then it dawned as high resolution fast. The idea is to run unbinned on one axis (intended to be RA for sure) and binned in Dec. I've never used it but it does suggest independent axis commands, no?

The simultaneous spikes Gina gets in both axes do need explaining in search of improvement, I think.

Olly

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Gina

Gina

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The simultaneous spikes Gina gets in both axes do need explaining in search of improvement, I think.

Olly

I'm currently rebuilding my pier head power distribution box with the aim of stopping electrical interference and voltage drop, particularly on the 5v supply to the USB hub.  I think the spikes are due to interference so very much hoping this rebuild will cure the problem.

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ollypenrice

ollypenrice

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I'm currently rebuilding my pier head power distribution box with the aim of stopping electrical interference and voltage drop, particularly on the 5v supply to the USB hub.  I think the spikes are due to interference so very much hoping this rebuild will cure the problem.

This does sound like a good fit for explaining it.

Olly

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russellhq

russellhq

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There appears to be an option for changing the angle but I haven't tried it.  It's been giving an angle of -138 degrees.  I was thinking of setting the Lodestar to orthogonality and seeing what the angle box says.  Then I'm wondering if it could be set manually to the nearest of 0, 90, 180 or -90 degrees if it isn't already on one of these.

Couldn't you plate solve your guider image to determine the rotation? That may give a more accurate result.

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Gina

Gina

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It's quite easy to align the guide camera orthogonally to the RA/Dec axes within a few degrees by eye.

I had another go last night after PHD refused to perform but total disaster! :(  I don't know what the problem was with PHD - in the few times when the sky has been clear in the last month or so, it's been working well enough that I haven't bothered with the more complicated AA5 for guiding.  Once I'd gone out to the observatory last night and checked where my rig was pointing and put that right (it was pointing at the side of the obsy wall! :( - I think that's another problem :() I was able to plate solve in AT and get my target in frame and centred.  PHD showed a perfect star field from the Lodestar with a couple of clear bright round stars.  But the calibration was strange in the N/S direction (fine E/W) and the guide graph traces wiggled their way towards the floor :(

post-13131-0-04883400-1418030618.jpg

So I thought I'd give AA5 another try (that's why I'm posting about PHD in an AA5 thread - I'll post another thread about my PHD troubles).  Strangely the AA5 image from the Lodestar X2 was very noisy with a number of stars barely showing above the noise.  I put my square round the best one but the guide view showed the star right at the lefthand side of a very pixelated and noisy display and it wouldn't calibrate.

So the puzzle related to AA5 is why is the image from my Lodestar X2 virtually perfect in PHD but very noisy in AA5?  Both binned 2x2 and both set to 3s exposure time.  I don't understand why there should be any difference.  Further checking was defeated by cloud.  After trying AA5 I did go back to PHD to check that the image was still good and it was - very good.

I welcome any thoughts on this :)

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