Hi John,
Not sure what camera you are using, however if you have a Lum filter in the filter wheel, you might find it easier and more reliable to focus with the Lum filter and use filter offsets to then set the focus position for the Ha filter. You can determine the offset using a Bahtinov mask to find best focus for each filter. You then tell SGP the difference between the focus steps for the Ha vs the Lum.
I think that's what the SGP boys recommend and that works for me.
Peter
|