completed horizontal offset test (Halifax)

I wanted to revisit offsetting with the Burke-Gaffney Observatory so to effectively produce a mosaic for the Rosette Nebula. I had some trouble with a past attempt... I don't think I had my wires crossed; I think the 'scope-mount went in the wrong direction. I wanted to be clear how the offset feature worked.

The documentation says use:

offset=offsetra,offsetdec

where a positive:

• offsetra positions east, and,
• offsetdec positions north.

I decided to overlap by 10%.

I chose HIP 31130 for the centre of the mosaic.

All images full size, in luminance, 60 second subexposures, 10 stacked shots. FITS Liberator, GIMP. North is up; left is east.

Of course, the centre image uses offset=0,0. It was captured at 22:38:17 AST.

The right frame was captured with offset=-90,0 on 23:12:46 AST.

And the left panel used offset=90,0, acquired at 23:55:57 AST.

It worked!

Well, the horizontal bit is fine. The -90 in the RA offset went west (right) with a decent overlap and the +90 went east.

But... why the heck did the image shift to the south?! Bad pointing? Bad plating solving? I didn't not request this. And it's a lot! If I'm trying to do a mosaic with just 10% overlap, uncalled shifts like this might leave gaps... Ugh.

And why the heck was I getting rectangles?! I looked up the specs of the SBIG camera. Oh... not square. The SBIG STXL-11002 is working at 2004x1336 (binned by 2) in full frame mode. Dang. That will impact the mosaic vertical plan...

It's also lookin' like I'm clipping the east and west edges of the nebula...

I also gathered RGB data.

Bad donuts. We need new flats...