Is my maths correct....?

[Stuart1971]

Hi,

am trying to work out some settings for autofocus, and wanted some input in case my maths it wrong, as it’s not my strongpoint...

First of all critical focus zone, my scope is an f5.3 and my camera has 7.8 micron pixels, so am I correct in saying that the CFZ is approx 70 microns..?

Secondly working out what size each step is from my focus motor, which is a Pegasus, to move tube from fully in to fully out is 20,000 steps, to move the tube 15mm it is 7086 steps. So I calculate this to 0.0021 mm per step, or 2 microns, is this correct, if so does that mean I have 35 steps in the CFZ....?? 😀

hope that all makes sense, as it seems to in my head, but if someone could clarify I would be grateful 👍

[wornish]

This might help

http://www.wilmslowastro.com/software/formulae.htm#CFZ

The formula there confirms your number for the size of the CFZ is 70 microns.

 If 7086 steps moves the tube 15mm then the distance per step is .0021 mm correct

and yes you therefore have approx 35 steps in the CFZ.

 

Your maths seem fine.

 

 

Edited April 17, 2020 by wornish