I have been working some guiding issues with the PHD2 folks. Their software reports the image scale of the ST-i when guiding through the kit's cctv 100mm lens as "15.26 arc-sec/px". It is their stated opinion that this scale is too rough and is "ridiculous". I have not been dissatisfied with the performance of this guiding solution (I attach the kit to a TMB80 SS piggybacked on a Meade LX200). However, the ST-i probably won't last forever. I would like to know SBIG/Diffraction Limited's recommendation for a proper imaging scale for a guiding camera. --Pieter Strauss PS when imaging through the LX200 itself, I guide with the ST-i mounted in the 8300 OAG.
What's the main imaging scope optical parameters? What mount do you have? (LX200 classic? LX200GPS? or a GEM?) It's not "ridiculous" if your seeing conditions are 1 to 2 arcsecond/pixel, as the guiding software should be using a centroid calculation. If you are doing high magnification stuff (e.g. 3000mm focal length), then it's not ideal, we'd recommend going off-axis with an SBIG StarChaser SC-2.
You can easily guide at 20X lower resolution than the main camera. The guider algorithms use a centroid that can measure to much better than 1/10th a pixel.
Sorry, forgot I needed to supply more info. In this case, the ST-i kit is hard mounted on a TMB80SS (80 mm, f6.3, focal length 504mm), and the 8300M with filterwheel is mounted on the TMB80SS. There is an Astrotech field flattener, then a spacer, then the 8300M. The TMB80SS is ring mounted (Losmandy rings) on a Losmandy plate bolted to the top of the LX200, which is the 10 inch ACF GPS model. So the ST-i is sending guiding images to PHD2 on a PC via USB, and PHD2 is sending the move information to the LX200 mount via a USB adapter and a serial cable. PHD2 now prefers to send guiding commands to the LX200, rather than have them go through the ST4 port. In PHD2 the ST-i is set to take 3 second images. For your information, PHD2 reports the following RMS RA 3.49" (0.23 px) DEC 2.55" (0.17 px) Total 4.32" (0.28 px) Also FYI the problem I am working on is the fact that the TMB80SS produces star images which are flat on one side (the top, I believe). I have been working on this for 10 years, and think it is time for a new telescope!
