I have a problem with Autofocus.
My equipment is:
- Takahashi TSA-102 + Reducer/flattener
- QHY9 Mono camera
- OAG + Filterwheel
- Seletek Armadillo focuser
My problem is that I always get elongated stars at corners.
The V curve is fine, but the real focus point is always 30-40 motor steps outer from the Focus Routine result.
Previously I had a TS 130 refractor with the same imaging equipment and I never had that issue.
The focus was always correct.
The takahashi TSA-102 has a very thin focus plane, so the V curve has to be very accurate.
I defined the steps size , number of steps, minimum star size, etc as stated at the help file of SGP.
Once I got the autofocus automatic point, if I manually move the focuser 30-40 steps out side, the elongated radial stars disappear and the stars at corners are round.
Investigating a little, if I take after focusing the saved files, and open it at SGP and calculate de HFR, the theoretical focused image has a higher HFR than the previous one (40 steps higher)!!
- different steps (9, 13, 15)
- also different distance between steps (30, 40, 50)
- also changing Bin 2x2 to Bin 1x1
- and also changing the minimum star size (4, 6, 10, etc)
Always the focused image has elongated radial stars at corners.
The resolution of the focused central part of the image is poor compared with the image I got if moving manually the focuser 30-40 steps.
I though it was a problem of Backfocus distance from the reducer to the CCD plane, but after trying several rings (5mm, 10mm, 15 mm, 1mm, 0,2mm, 0,3mm etc) the result is always the same.
I can attach some AF saved files and two images, one with automatic focus, and the other moving the focuser out side.
For example, if you see tha AFPack_376, the focus point is about interval 7 (See V image). But the interval 6 has a lower HFR if you open it in SGP. But in the V curve, the Interval 6 has a higher HFR!!
Also the log file for the session.
Thanks a lot
sg_logfile_20170309202338.txt (1019.0 KB)