Re: Guide star lost after dithering

Roland Christen

A dither move is normally the same as a guide move command, except typically bigger. If the mount guides normally and properly, then it is responding to the PHD external commands in the proper manner. I don't see how the mount would, on its own, move the Dec axis by 12 pixels unless instructed to do so.

If the camera is angled by 45 degrees then both X and Y will move although only RA is commanded to move. We don't have enough information at this point as to what really moved. Did the Dec actually move or did the Y axis of the camera move? The two are not the same. People often mix up the X and Y axes, thinking they are the RA and Dec axes. This is not the case unless the camera is exactly rotated to a null position with respect to RA and Dec. That is usually never the case.


-----Original Message-----
From: Brian Valente <bvalente@...>
Sent: Tue, Nov 23, 2021 8:30 pm
Subject: Re: [ap-gto] Guide star lost after dithering

Regarding your image download when exposure complete, are you still guiding while image is downloading? Does download take a while?

On Tue, Nov 23, 2021 at 6:28 PM yanzhe liu <liuyanzhe@...> wrote:
Yes, exposure time was 900s.

On Tue, Nov 23, 2021 at 6:25 PM Brian Valente <bvalente@...> wrote:
Are you doing 15 minute exposures?

The dither distances and settling look fine from a PHD perspective, although I can see a big spike in guidestar SNR roughly every 900 seconds

On Tue, Nov 23, 2021 at 5:49 PM yanzhe liu <liuyanzhe@...> wrote:
Here is the log:

I have not used the log before but I think this is the dither causing issue. I then restarted the sequence by turning dither off.

19:29:39.383 00.003 2112 PhdController::Dither begins
19:29:39.386 00.003 2112 dither: size=1.00, dRA=-0.61 dDec=0.00
19:29:39.389 00.003 2112 MountToCamera -- mountTheta (3.14) + m_xAngle (-1.59) = xAngle (1.55 = 1.55)
19:29:39.392 00.003 2112 MountToCamera -- mountX=-0.61 mountY=0.00 hyp=0.61 mountTheta=3.14 cameraX=0.01, cameraY=0.61 cameraTheta=1.55
19:29:39.395 00.003 2112 setting lock position to (121.19, 18.76)
19:29:39.398 00.003 2112 Mount: notify guiding dithered (0.0, 0.6)
19:29:39.401 00.003 2112 MultiStar: stabilizing after lock position change
19:29:39.403 00.002 2112 Status Line: Dither by -0.61,0.00


Brian Valente


Brian Valente

Roland Christen

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