Focusing with a narrowband filter

[smr]

Hi,

I'm just wondering if anyone can advise on the best way to focus with an Optolong L-eNhance Filter and a 600D modified Camera.

I've got a Bahitnov mask for my Z73, and without the filter it's as easy as choosing a bright star and being able to focus with the diffraction spikes.

With the Optolong filter that option isn't available and I'm not sure how best to try and achieve focus. 

I've tried using the Bahitnov aid in APT but it's difficult to know whether it's actually in focus as it jumps around so much, probably due to atmospheric turbulence.

[discardedastro]

Honestly, the best approach I've used is either long focus exposures - which will average out atmospheric turbulence - using software to measure FWHM or similar. That combined with using parfocal filters and focusing with L, which is never going to be perfect but if you've got a motor focuser and parfocal filter system is a pretty viable option.

For the 600D you should be able to take 10s exposures or similar and get a reasonable exposure on a mask.

[smr]

30 minutes ago, discardedastro said:

Honestly, the best approach I've used is either long focus exposures - which will average out atmospheric turbulence - using software to measure FWHM or similar. That combined with using parfocal filters and focusing with L, which is never going to be perfect but if you've got a motor focuser and parfocal filter system is a pretty viable option.

For the 600D you should be able to take 10s exposures or similar and get a reasonable exposure on a mask.

Thanks for the reply. Just finished focusing on Vega. Actually a lot easier than I thought, 5 second exposures and it's so bright it makes focusing really easy. Had to take a few photos to get it right but worth doing to know it's in focus.