Parse the log file for focus positions?


Does the log file record what position an autofocus settled at ‘best’ focus for each filter?

I am thinking maybe this data could be used to determine offsets.

What key words would I look for to extract such data?


It might be easier to extract this information from the fits header if your images. I’m pretty sure there was a thread on here not so long ago where someone created a script in R to do exactly that and work out offsets.


Just found it:



If you enable “Image History” you will get everything you need:





If you wanted to setup a “wizard” kind of routine, create a test sequence that targets a nice star field. Create an event for each filter which takes one, short frame through each filter. Set the AF routine to auto focus on start and on filter change. Enable image history.

For an LRGB setup you would get four subs in pretty quick succession. This helps with temperature changes between exposures that could give false readings of the relative offset positions. From Image history, you can get the focus position of the LUM filter and the RGB filters. Putting this data in to the filter wheel setup should allow SGP to do filter offset focusing. To be perfectly rigorous in this, run the sequence multiple times and take averages of the focus positions.



Thanks guys all great ideas. I will have to look into them!

As it turns out I do have image history enabled but did not realize that all that data was available to me!

Special thanks for that!


Okay a few more questions on this.

Once I parse the data and get focuser positions for each filter I simply enter those positions the “Focus Point” field of the Filter setup? Then SGP calculates the difference for the next called filter?

What happens if say one day I dis engage the focus motor to do some planetary with a different camera and no filters using manual focusing then later re-engage the motor. The motor and focuser will of course be in a different position. Would that invalidate the data entered?



I am not sure I correctly understand the internal SGP procedures but basically once you have put in those absolute focus positions, SGP can calculate the number of steps between the LUM filter and any of the RGB, SHO filters. When SGP is focusing for the RED filter, for example, it will actually focus with the LUM filter. Then look in the filter setup to see the difference between the LUM and RED filter data stored there and apply that same difference to where ever the LUM filter just focused.

You probably can’t make any changes to the hardware without invalidating those focal positions since they are absolute values that are unlikely to be duplicated by a different setup.