SGP for Collimation


I recently went through the process of collimating an RC and through the different methods it seems that the final confirmation, or even the best way to collimate, is through a defocused star. I’ve also read that to be very accurate you’ll need to test all four corners. Many will use an eyepiece. But with the ability to refresh the image and stretch it I found it quite easy to discern the diffraction pattern using a CCD. That all said it is quite a pain for slew and defocus in/out, focus again slew, etc…
I was thinking that the Mosiac wizard could be useful to setup 5 boxes, overlapped that could put the bright star in the the center and all 4 corners of FOV. Slew to: would be the quickest, don’t think you’d need to plate solve. The problem in automating this though would be the focus. Is there any way to automatically force the stepper to move to a specific intra/extra focal positions to expediate this? It wouldn’t take but a few mintues to figure out how far each specific scope/focuser would need to move to be appropriately defocused.

I think that everything needed is already in SGP, but to do this but would take some type of scripting to perform automatically. Hence “Feature Request.” There may not be enough interest in this but for me, after I slew to a bright star for my first quick focus and sync of the night if there was a “Check Collimation” button that could automatically slew to a bright stare, move the focuser to the predetermined focal position, take a shoot, move focuer the other way take a shot, slew each corners, take the shots for each of those and save these images so I could review collimation quickly.

Just a thought. Or am I over thinking this process?


I think this would be super helpful and I would use it, but I wonder if
enough users would find this beneficial to warranty an actual feature in
SGP. Good idea.


i think this would be very useful too. even without any focusing involvement, just the ability to quickly put a star in each corner of the chip (and the center) would be a huge time saver.


This would be very useful also for checking the tip tilt for fast systems. Currently you need to slew manually the same star to each corner and it takes forever. This would require an option with no adjustment to autofocus.


That sounds like a great option. +1 for me.


I thought about it more. I think that FILTER OFFSET could be used for the defocus. If I setup two filters and set their offsets at the way outer focus and inner focus select those for each sub take the shots then slew to the next target and do the same.


I would use the heck out of this feature. +1


I don’t think it is as useful as you believe. I wrote an exhausting evaluation of RCT colimation techniques in my book. I budgeted for 5 pages and ended up writing 25. The analysis of out of focus stars is an excellent one but requires really good seeing to work well. I sometimes have to take a dozen images to get one that is reasonable to assess. Combine that with slewing to corners and it starts to become cumbersome. The way I ended up doing it was to try and find a loose cluster at high altitude, it would fill the image and I could alter the primary mirror without worrying about it slipping sideways (as the cheaper models tend to do). With the big image, it is easier to scan all the stars and with a little practice, the eye notices where the stars are more pointy, indicating a likely secondary change.