Hi Rod
When I first saw your image, what struck me was the brightness of the secondary star and what appear to be diffraction spikes on that same star.
So, as I’m just at a computer screen looking at a 2D B&W image, that’s about all I can really say as I wasn’t there on the night, so I really don’t know. What I have written is just my guesswork and some speculation but gee, I’d be so very happy for you if that were the Pup!
I guess one approach would be to establish the apparent field of view and we can do this at F15 and also F25 and plug the numbers in, assuming you were using the Meade LPI, and this is the full frame. The FOV would be something like the following, based on a chip 640x480 with 7.5 micron pixels:
150mm F5 with x3 Barlow giving 2250mm at F15:
FOV is 7.3 x 5.5 arcmin at 0.69 arcsec/pixel.
150mm F5 with x5 Barlow giving 3750mm at F25:
FOV is 4.4 x 3.3 arcmin at 0.41 arcsec/pixel.
So, using a separation of 8.75 arcsecs for Sirius A & B;
At F15 the Pup would be some 13 pixels from Sirius A,
At F25 the Pup would be some 21 pixels from Sirius A.
Hope that helps and mate, thanks for not spitting the dummy
; as I previously wrote, my comments are pure speculation and only my best guesses, and thus do not detract from your work at all.
Cheers
Dennis