Star Alignment fails

[MHeigan]

Hi all,

I imaged a few targets at a dark site last weekend with my Canon 60Da. Our skies are just starting to clear, and I did a series of short 30 second - 2 minute exposures for practice.

I decided to up my usual setting of ISO 1600 to ISO 3200, to allow for slightly shorter exposures. As a result the images are understandably a bit noisier than usual, and the stars are a bit brighter than I typically get, but the results are still acceptable to me for getting practice. The only other variable is that the last SGP update changed my capture format to CFA FIT, rather than the usual CR2 RAW.

To my surprise, I am now struggling with Star Alignment via the Batch Processing Script and even manually via the Star Alignment Tool.

I tried the usual recommendations:

In the Batch Processing Script I tried Lanczos 3 and Bicubic Spine with a reduced clamping of 0.1, but it still returns the error:
Error: RANSAC: Unable to find valid set of star pair matches.

I manually tried additional settings in the Star Alignment Tool, like lowering the Log Sensitivity value and increased the Maximum Distortion Value, but to no avail.

Any other ideas or suggestions?

Just as a test I ran it through DSS with default settings, and it has no problem, but I really don't want to resort to that..!

Regards

Martin

[vicent_peris]

Hi Martin,

Which is the focal length of your telescope?


Best regards,
Vicent.

[MHeigan]

It is a wide field Astrograph - 600mm at f/4.

Regards

Martin

[pfile]

during my travels i found out that when SGP saves a fits file, it first scales the data to 16-bits.

pixinsight always handles DSLR frames in 14-bit format.

if you made calibration frames from the CR2s they are not compatible with the FITS lights... you'll have to recapture some calibration frames as FITS from SGP.

rob

[MHeigan]

Thank you, I read something similar on the SGP forum, and recaptured calibration frames last night. I will test it this evening.

Regards

Martin

[pfile]

your case is exactly why i asked them to put in a switch to not scale the CR2 data before writing the fits. they said they would consider the change. what's clear is that DCRAW has interpreted the file dimensions the same between SGP and PI; the SGP developers had argued that probably the X/Y dimensions of the fits created by PI and the fits created by SGP would differ thus rendering the FITS files produced by SGP incompatible with PI... but they could not have differed or BPP would have died during the ImageCalibration step.

so that only leaves the scaling as a source of incompatibility. if they got rid of that, you'd be able to interchange CR2 files with SGP FITS in pixinsight just fine.

rob

[MHeigan]

Thank you for the info, now my Calibration fails.

I will try and take it up with SGP.

Regards

Martin

[Harry page]

Hi

Can you lets us see a couple of the problem subs

Harry

[pfile]

SGP forum probably won't help, as harry says post some subs here and we can see what's going on.

rob

[MHeigan]

Thank you, I posted on the SGP forum anyway. I am giving it another try now again. If I still get nowhere, I will post some subs.

Thank you again for the willingness to help.

Martin

[Juan Conejero]

Hi Martin,

As Rob says, this is probably a FITS compatibility or data scaling issue. However, please realize that without looking at the images it is impossible to say anything useful here.

[MHeigan]

I managed to get it working in the end by re-shooting all calibration frames in SGP in the same format and starting from scratch. CFA FIT isn't compatible with any other format (even after format conversion), but if it is all you use, it seems to work. So much for my extensive RAW Dark and Bias Library..

Regards

Martin

[pfile]

i think with some effort it can be made to work... for instance if SGP's scaling is exactly linear then you could probably reconstruct the original 14-bit values, albeit with quantization error.

but in general unfortunately you have to stick to the same format. "the great thing about standards is there's so many to choose from!"

rob