|
Hi Bram et al,
Yes, there is a critical range for focus which is intimately dependent on your telescope optical speed, below is a table giving the critical depth of focus for scopes of various speeds.
So for example my Crayford on my solar scope was to hand and moves by 6mm with five turns of the 10:1 input control so ...
6000um / 5 = 1200um / revolution
SharpSky generates 2880 steps/revolution => 1200 / 2880 ~ 0.42um/step
The scope is about f/8 so that is 184 / 0.42 ~ 438 steps to cover the complete critical focus range of the scope - more than enough resolution to accurately nail focus.
Hope that's correct and makes sense ?
Clear skies,
Dave
Focal Ratio Depth of Focus
f/2 12 microns
f/3 26 microns
f/4 48 microns
f/5 72 microns
f/6 104 microns
f/7 141 microns
f/8 184 microns
f/9 233 microns
f/10 287 microns
|