Plate solving fails for Watec 120N+ video camera images

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Murray Forbes

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Mar 3, 2024, 2:00:23 AMMar 3
to astrometry
I have not been able to plate solve the attached image, nor any other images from the same scope & camera setup.

Background:
The Watec 120N+ is an integrating, analogue video camera commonly used for recording occultations. It outputs an old-style PAL TV video stream through a GPS time stamp insertor, video-to-USB convertor and finally recorded by SharpCap as a series of FITS files (one attached). I have also tried this with the OccuRec video recording software. The image is a standard PAL size (795 x 596). Normally a PAL signal is 8-bit depth but as the Watec is an integrating camera it is 16-bit depth. The image here is of a well-known southern hemisphere open star cluster Kappa Crucis, at RA = 12h 53m 42s, Dec = -60d 22.0'. The Field of View is 30 arc-minutes x 19 arc-min. I have also tried the plate-solve without the time stamp added to the bottom of the image but get the same result (a failure in the plate-solve).
Kappa Crucis_01139 12_23_43Z.fits

Dustin Lang

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Mar 4, 2024, 9:50:39 AMMar 4
to Murray Forbes, astrometry
Hi,

Interesting, the image looks fine, the source detection looks okay, so I'm not sure what is going wrong.

Are the pixels square?  Rectangular pixels are one thing that Astrometry.net can't deal with at all.

cheers,
dustin


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Murray Forbes

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Mar 5, 2024, 1:40:26 AMMar 5
to Dustin Lang, astrometry

From memory, I think they're very slightly off square, but would need to double check.

Cheers,

Murray.

Bryan

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Mar 5, 2024, 9:47:13 AMMar 5
to astrometry
Slightly off-square... 8.3 microns x 8.6 microns


Bryan

Dustin Lang

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Mar 5, 2024, 1:30:42 PMMar 5
to Bryan, astrometry
Okay, that fixes it --
I trimmed the bottom off, and then scaled it horizontally by 1.036
(fitstopnm 1.fits | pnmscale -xscale 1.036 | ppmtopgm | pnmtofits > 2.fits)

And I get this solution:

cheers,
dustin


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