asi294mm fits header bug affects ASTAP plate solving
Posted: Tue Feb 28, 2023 4:13 am
Hi Robin,
I believe I've found a bug in the fits header SharpCap generates for the 294mm pro. I loaded the latest asi driver and sharpcap for testing. This may be a ZWO driver bug or a SharpCap bug.
Plate solving from SC was mostly failing. So I looked at the header and tried the ASTAP app directly on capture subs. I am using an RC with FL=2026mm and an AstroPhysics mount with the ASCOM driver. The 294mm is using the "standard" 4144x2822 resolution binned 2X2. The resolution spec is 4.63 microns square per pixel.
In the fits header, naxis1=2072, naxis2=1411, so these are including the binning. I don't know if that is correct. ypixsiz=4.63, the comment field says /microns, includes binning. same for xpixsz. That does not include the binning, which would double the value to 9.26microns.
ASTAP mostly fails, but occasionally works and gives the following warning: "Inexact scale. Set FOV=.37 or scale=.9"/pix or FL=1014" So the image scale is apparently calculated off by a factor of .5. If I go to the Solve settings, the "Field of View (height) deg parameter was showing .18 deg, which is half the correct height. If I change it to .36, solving always works.
So, it seems that one of those header params is wrong, most likely the 2 pixsiz values, which don't include binning.
Not sure if this is SharpCap or ZWO, since I don't know how the figures are being used.
Here is a link to a sub on my google drive if you want to check this out. Too big to just attach:
https://drive.google.com/drive/folders/ ... share_link
best,
Steve
I believe I've found a bug in the fits header SharpCap generates for the 294mm pro. I loaded the latest asi driver and sharpcap for testing. This may be a ZWO driver bug or a SharpCap bug.
Plate solving from SC was mostly failing. So I looked at the header and tried the ASTAP app directly on capture subs. I am using an RC with FL=2026mm and an AstroPhysics mount with the ASCOM driver. The 294mm is using the "standard" 4144x2822 resolution binned 2X2. The resolution spec is 4.63 microns square per pixel.
In the fits header, naxis1=2072, naxis2=1411, so these are including the binning. I don't know if that is correct. ypixsiz=4.63, the comment field says /microns, includes binning. same for xpixsz. That does not include the binning, which would double the value to 9.26microns.
ASTAP mostly fails, but occasionally works and gives the following warning: "Inexact scale. Set FOV=.37 or scale=.9"/pix or FL=1014" So the image scale is apparently calculated off by a factor of .5. If I go to the Solve settings, the "Field of View (height) deg parameter was showing .18 deg, which is half the correct height. If I change it to .36, solving always works.
So, it seems that one of those header params is wrong, most likely the 2 pixsiz values, which don't include binning.
Not sure if this is SharpCap or ZWO, since I don't know how the figures are being used.
Here is a link to a sub on my google drive if you want to check this out. Too big to just attach:
https://drive.google.com/drive/folders/ ... share_link
best,
Steve