Hi Bernd,

Thanks for replying. On the standard deviation:
1. If single star mode is selected, the SD option is disabled.
2. For multi-star... the stars go through an extraction process to find suitable candidates (I haven't changed this). There are several options but if you use the default SEP there are many parameters to control this, for example removing clipped stars and those below a certain brightness. After this process has run there will be a set of stars that meet the criteria and each has its HFR calculated. I then calculate the SD of this set.

The star set will vary from frame to frame and there is some existing work in Linear to try and use the common subset of stars for consistency. I am trying to use this in Linear 1 Pass, but there is still some work to do. Variation in brightness of the stars should not affect the HFRs too much (assuming the extraction and processing parameters are set reasonably).

The variation in HFRs will depend on focus effects, seeing, etc. but I think its a reasonable measure of "quality" for the focus point. What I've observed on my equipment is a trend whereby SD increases with distance from optimum focus but then certain points deviate from this with transient effects like seeing, wind gusts, etc etc.

As to whether applying weighting makes enough of a difference to the calculated optimum focus point to be noticeable, I don't know. We'll just have to give it a try.

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