I have a TEC 140 on a Paramount ME with a SBIG ST-10XME. Lately I have been getting particularly disappointing results and wrestling with nearly every component in the complex system.
Taking one problem at a time, recently I have been focused on trying to get my big expensive mount to do 10 minute unguided subs. According to Software Bisque's T-Point claims, that should be easily doable with a 1000mm focal length.
But I have been getting quite oblong stars unguided for five and ten minutes, although ten minutes no worse than five.
I am using TheSkyX Pro.
The mount is on a cement pier inside an observatory dome and the polar alignment is ranked good in T-Point. My setup's image scale is 1.43 arcsecs/pixel.
I recently re-lubed the mount as illustrated in the online video "Lubricating the Mount by Software Bisque." In T-Point I ran a 330 point session and ran the super model to get Sky RMS = 9.3 and PSD = 9.7. Quite good I think. Protrack is activated and enabled. I also ran a periodic error training as per Richard Wright's "Training Periodic Error (PEC) on Paramounts" video. The results were poor. A 20 minute log training session with PEC off gave me a 4.2 arc seconds peak to peak fitted curve. I saved that to the mount for PEC and ran another session with PEC turned on and the results were somehow worse at 5.9 arcsecs peak to peak.
None of these efforts helped my oblong stars.
I have a long thread going now on Software Bisque's forum here. There was a question about orientation of the scope or possible mirroring of the image for the PEC training runs. An image was checked and they are not mirrored. Tonight, with better seeing than recently, I created some new autoguiding PEC training logs as per Richard Wright's video. As per the video I am using my primary scope and camera as the autoguider. Log 1 was taken east of the meridian with a LUM filter, one second exposures, for about 20 minutes and with "Apply PEC" not checked, i.e. with PEC off. It plotted out at 4.1 arcsecs peak to peak.Still in the east, still near 0 degrees declination, log 2 was made with log 1 saved to the mount for PEC and PEC turned on. It plotted out to 7.8 arcsecs peak to peak! Not as it should be. Makes no sense. It could be that the correction was being applied upside down as it were. I went ahead and tried the reverse where a box in the Bisque Telescope Control System is checked that the scope was pointing west (even though it was pointed east). With PEC turned on log 3 plotted out at 7.7 arcsecs peak to peak.
I considered giving the mount a breathalyzer test.
I went through the whole process again. Same results. No PEC = 4.2 arcsecs peak to peak. With PEC turned on twices as bad at 8.0 arcsecs peak to peak. With PEC and west box checked, 8.1 arcsecs.
In other words, the PE is better (but not good) when PEC is turned off.
That begged the question of what does a long exposure look like with PEC turned off. I had not tried that before. With a lot of moon out tonight I used an Ha filter and focused with that filter using @focus3. A 60 second exposure looked pretty good! The stars may be a little fat but they were round with a FWHM measure of 3.4. I think that is in pixels so at 1.4 arcsecs/pixel in my camera, pretty fat. But round. 300 seconds measured 3.4 also. 600 seconds were starting to become oblong but much better than it had been and a FWHM of 4.5. This is much better than I was getting unguided with PEC turned on.
This big, expensive mount should do better and it is odd to say the least that it works better with PEC off.
I'd love to hear anybody's thoughts.