Optimal moving primary position

My 10" f/12.5 APM Mak-Cass has Intes Deluxe optics and Matthias Wirth tube & mechanicals and is a moving-primary design. I've added a FeatherTouch for fine focus as well.

Can anyone tell me what is the optimal position for the moving primary - that is, what was the optical design likely optimized for - in the middle of the focus range, all the way forward or all the way back?

thanks,

Eric

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Only the designer of the optics has the info that you are looking for.

Generally speaking the optimum design location for the moving primary Maks is somewhere between the two extreme primary positions and that is also where you get the F/12.5, beyond that point the F ratio will also change and depending on the amount of movement allowed the F ratio will probably go approximately from F/11 to F/14 on your scope.

Vahe