I took a lot of dual band filter data last night trying out a lower ISO setting than normal on my DSLR. I’ve had success with 30 seconds at ISO3200 for the sv220 filter but last night I did ISO1600 (and also on a higher focal length telescope, so it was really not a good idea, I know…).
Looking at the individual frames I can stretch them and see all the stars I’d expect to see in the frames and I can even see the faint details of M101 that I’m trying to pull out by stacking… but the standard OSC_Extract_Ha(OIII) is failing with some Not enough star pairs (7): Image 55 skipped and (mostly) Cannot perform star matching: try #3. Image 56 skipped style errors.
As an example, this is a very typical stretched sub, so I’m hopeful I can get the star detection working…
Is it possible that the reference image is just bad somehow? How do I find out which sub is designated to be the central origin/zero point?
Can somebody please help me understand how I can get the star detection working here? I’ve only been doing astrophotograpy for a week and this one has me stumped. I’m guessing I might need to do the align / stack steps manually instead of running the script?
After dark subtraction, the image contains many negative pixels (27%), calibration frames are probably incorrect
I’ll double check what I’m using as my darks.
UPDATE: the calibration frames seem fine. Darks and biases are all within the average pixel ranges I’d expect. The flats were taken with a very long exposure and are quite bright (aperture priority said so, maybe I should have dialed it down), it’s possible that is messing with things. I’m hacking the script to run without the flats, as they seem to be the most likely candidate to be broken…
I think there wasn’t enough signal, so I wasn’t able to process with darks. I created a script to process without the dark calibration frames and it was able to stack a couple of frames…
I’m still getting Not enough star pairs (8): Image 101 skipped in most of my frames, so this means manual registration with more liberal parameters? Looks like I can reduce the number of star pairs for sure.
UPDATE: reducing from 10 to 5 stars already gets me from 13 frames to 188, which is still less than 50% of my subs but that’s a start.
UPDATE2: manual registration and picking 3 stars seems to be working quite well. I’m getting about 3/4 of my subs registered now.
If you have 27% of negative pixels, something is probably wrong with the darks, unless you’re shooting exposures less than a second. That will cause all sorts of problems.
If all images look like the one you posted, you need to change the detection settings indeed because stars don’t look like stars, collimation and focus are probably bad. Use the ‘relax checks’ option
