Last night I experienced something that happens occasionally. Some clouds rolled in causing the sequence to abort and recovery to engage. Normally this works well and last night recovery restored the session without trouble once the clouds cleared. However, when it did so, the frames it collected after recovery were significantly off-center. I have watched this happen before and the cause is PHD2. It will struggle to recover a star, and it sometimes finds a bit of noise or something and tried to correct. Before long, it is hopelessly lost and may have moved the scope a good bit. I imaging that I also get some drift if the mount tracks unguided for as much as 90 minutes.
This could be corrected by having a “Center after Recovery” option. So that’s my feature request.
It takes a little bit of finessing to get PHD2 immune from hot or warm pixels when clouds come by. Make sure you are using a dark library, and, if necessary, re-build it to make sure any new hot pixels are covered. Or, use a bad-pixel map and manually add any new hot pixels as they show up. You can also use the minimum HFD threshold setting to exclude hot pixels. For more info about these options see the PHD2 user manual, or post in the PHD2 Forum. When PHD2 is setup properly with a good dark library or bad-pixel map and an appropriate minimum HFD setting then you should be able to take a frame with the camera covered or taken on a cloudy night and select Auto find star (Alt-S) and PHD2 should fail to find any star. In other words, it should be able to properly reject all hot pixels. It’s good to test this ahead of time (like on a cloudy night) so you can be confident that you won’t be locking on to hot pixels if clouds come by during an unattended imaging session.