I have a celestron OAG. I love how large it is, lots of stars usually to pick from.
I have a problem I cannot seem to solve. When there is a bright star on the main sensor, I get a weird circular artifact on the OAG frame. PHD2 star selection identifies parts of it, sometimes, as a star. if it gets elected as the guide star, either my guiding becomes perfect or more frequently it decides it needs to move a tiny bit - - and a bit more -- and a bit more... never actually seeming to move and it guides way off the target.
I can tell you what it is not -- it is not something on the prism, or the sensor of the guide camera. I have taken it apart many times and found nothing.
Someone else who had this said moving the stalk further out (away from the frame) solved it -- I tried that today and it actually got worse. I moved it far inside, just barely outside the full frame sensor. A bit better but it is what you see below.
On many star fields there is no issue. The artifact does move, depending on where on the make frame the brightest star is.
The prism is rectangular, but the stalk looks round. I suspect the stalk is involved in this, perhaps the stalk/prism interface. But it looks clean and properly attached. I cannot figure out what to do to the OAG.
I've tried PHD2. I was lightly chastised in that group for not setting the Minimum HFD, but the HFD of the star-like pieces of the artifact compete with stars. I cannot find a value that excludes it.
I tried the ROI parameter (hidden) in the start-guide API from NINA. I think it is ignored for multistar though not sure. But it definitely does not work, it still searches the whole frame. The regular subframe option is not available with multistar.
I'm about ready to punt and shift to another OAG, though I hate giving up all that real estate (plus I have special precise part plumbing for two OTA's, which I hate to throw away as they are near perfect spacing).
Does anyone have any ideas?
This is what I get centered on the horsehead near rotation zero. Unfortunately there is often a bright star in many of the more interesting objects.
PS. If this belongs in SCT or somewhere else, moderators, I would appreciate it being relocated.
Edited by Linwood, 24 February 2021 - 09:39 PM.