Focussing with a H-alpha filter isn't easy when you compare it without a filter. I'm using a bahtinov mask everytime when shooting pictures. When using no filters, I'm using live view of my DSLR to see whether the star is focussed. In case of using my H-alpha or OIII filter it's getting difficult using live view. Even when I increase ISO levels and shutter time.
To conclude : I slew to a sharp star (eg Sirius, Vega, ..) with either the H-alpha or OIII filter and bahtinov mask and take a picture. Based on the picture I'm adjusting the focus and take another picture. I repeat this workproces untill the star is focussed.
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| Sirius in H-alpha and with Bahtinov Mask |
