Focussing canon+Ha filter - problem

[Demonperformer]

My normal focussing procedure with the (modded) canon:

1. Live view - enlarged - get dot as small as poss

2. Add Y-mask and take short 5-10s exposures, adjusting focus slightly to get diffraction spikes nicely bisecting.

Job done.

Just bought an Ha filter and thought I would give it a try.

However, live view showed nothing (not really surprised at that), and test exposures right up to 60s did not show any diffraction spikes.

So, any ideas on the best way to focus a canon when you have an Ha filter attached?

Thanks.

[Psychobilly]

Slowly...

I used to use a Bahtinov with a 35nm HA filter on the Megrez 72 at f4.8 Max ISO on the camera and 60+s exposures used to use the quick preview images and bahtinov grabber app... that was with modded (filter removed and filter replaced) cameras...

Billy...

[Demonperformer]

Mmm ... thanks for that ... so with a narrower filter and a slower scope ... maybe I will stick to using it with the H9, where the software tells me how in focus I am rather than having to get there by myself.

[swag72]

Look forward to seeing your pics with this - I am looking into getting one to tide me over until I can get a CCD!!

[johnrt]

I used to find the brightest star possible in the sky, use live view & zoom to get the star as small as possible in the viewfinder. I was using a 12nm filter and either a SW 150p or Megrez 72. Very dim, but it is possible.

[ollypenrice]

I used to find the brightest star possible in the sky, use live view & zoom to get the star as small as possible in the viewfinder. I was using a 12nm filter and either a SW 150p or Megrez 72. Very dim, but it is possible.

I'd do likewise, ideally using a star at a similar altitude as the target. But if you can't get a bright star to give a result then I wonder how much signal you are going to collect?

Olly

[Psychobilly]

It been a while but IIRC with the Bahtinov and the HA filter you got a Dashed rather than continous line...

I did a bit with HA filters and a Modded DSLR using 15 and 30 min subs... mainly on the Cygnus nebs...

Billy...