How do you focus with a narrowband filter?

[smr]

Hi 

I'm using a narrowband (for OSC) filter for the first time - I've never had one before - how do you focus with it ? It's in the field flattener of my Z73 (2" Filter) - whilst I can see stars I can't see any spikes with my bahitnov mask on.

Edited July 27, 2020 by smr

[JamesF]

I have to admit that I don't generally have a problem with this perhaps because I'm using mono cameras, but perhaps longer exposure times might help, or you might need to look to a different measure of focus accuracy such as FWHM?

James

[MarkAR]

10 or 12 seconds usually helps. I'm mono CCD as well so you might have to up the gain as well if longer exposures aren't enough.

[smr]

Thanks guys, I used the FWHM in APT and it seems ok - probably not in great focus but much better than it was. 

It's a new Camera I'm using, and a NB filter for the first time too so I'm having to learn a few new things at the moment. 

It took me ages tonight to get set up, very rusty having not set up since early May. 

Does it look like I finally got the Heart framed?

I'm wondering if this 600D that I've bought is ok as there are tonnes of hot pixels.

Clouds have rolled in now.

 

[MarkAR]

Dark frames will take care of the hotties.

[smr]

3 minutes ago, MarkAR said:

Dark frames will take care of the hotties.

Will dithering too as I don't take darks?

[MarkAR]

Dithering will help with background noise but you will have to take darks to remove the hot pixels.

For OSC I believe dark flats might do it as well but not sure.