Yes. How can I tell the difference between optical and guiding issues? Take a shorter test exposure?
My unrequested two cents... If there was, for instance, a collimation issue, one might see star trails on the outer peripheries (on a newt, for instance, star trails in the upper left quad would seem to point diagonally toward/away-from the center, upper right-quadrant to the right diagonal, lower left to the lower left, and lower right to the lower right) but relatively "artifact free" stars in the central area and the degree of streaking in each star would reduce as you near the central area of the image (there are also "unbalanced" miscollimations too, where it's worse on one side or another, so I'm not fully treating the idea)
When you see streaking in one direction throughout a field, it's likely (imo/e) tracking issues, as already noted by Tapio, although for a newt, alignment issues can contribute (especially, at least in my *personal experience, from the secondary mirror...I had a really sticky secondary mount on my first scope that would tend to **** (edit: idk, another word, skew? is that ok? roll? rotate?) itself slightly off perpendicular to the intended alignment.
And yes, shorter exposures can help to some degree when tracking is the issue. On my first scope, I used exposure lengths of 1-10 seconds to minimize streaking from tracking errors (with all concomitant thresholds on what I could image, even with large # frames stacking)
Sorry I misread. Maybe., You're using a refractor, right? you could use ether a shorter or longer exposure, depending on what the base comparison time is being used. For instance, if you were presently shooting with a 30 sec exposure, you could just fire up a 2 minute exposure and if tracking is the issue, you'll know it for sure. But if you're already shooting at 300 sec (5 minutes) , probably a short exposure would be easier.
Edited by xiando, 18 June 2021 - 02:09 PM.