I have been using ASTAP in SGP for a while with great success until last night. ASTAP would not plate solve on M13, the Hercules Cluster. My 9.25" EDGE HD SCT with a 0.7x focal reducer has a focal length of ~1645mm, so the cluster fills most of the field of view. I switched to Platesolve2 with no settings changes and it solved on M13 without any issues.
Mark W
Globs are a PITA when it comes to solving and focusing. I had similar issues and since I could not easily find any settings to fiddle with, I reduced the exposure, so the cluster was less distinct and used PinPoint, which failed similarly until I limited it to bright stars only. The exposure reduction idea might work with ASTAP too.
I figured as much. Thanks for confirming the difficulties with these objects, especially one as large as M13. I do find it interesting that Platesolve2 may be a little more robust than ASTAP. I do like ASTAP for its speed and I prefer it.
Note that ASTAP did plate solve a FITS file of M13 from my ZWO ASI1600 with the Lum filter, gain 75, offset 15 and exposure of 60 sec.
Mark W
I had exactly the same issue with M13 and a 10in Newt f4 at 0.67 arc-sec/pixel. ASTAP solved correctly intermittently. I’ll try reducing the exposure time.
Thanks for the tip!
–Luca
It does suggest that the focus target feature in SGP, which is often overlooked, might have a role in these special circumstances. In an ideal world, if a plate solve failed, it would slew to the focus target, focus and then slew/center back to the target.