Focus help concentrated Nebulosity

Sequence Generator Auto Focus
1

Hi,

Any advice would be appreciated. I’m taking a F5 sequence of the Tarantuala nebula NGC2070. It’s basically nubolosity intensive. I can get auto focus to get any real curve. Sometimes it’s flat, other times a “W”.
I’ve seen a few posts here where some people tried different filters with different exposure lengths.
My main technique is to focus with Lum then use filter offsets. I’ve tried HA and other filters, 5 secs up to 25 secs.
3 hours later I’ve just given up and slewing to a star field getting my curve and then going back.
I tried the Focus Target module which worked but not ideal as was suggested on another thread.

My equipment is FSQ106EDX native F5 with Atik 490EX
Astrodon 31mm filters. FOV 1.35 x 1.08 so pretty much solid NGC2070.

Perhaps temperature compensation is the best technique. Hard to get a 5 degree drop here these days though…

Thanks.

2

I have seen W shape before using the FSQ106, with FocusMax. It is more of a V with a slight kink at the bottom. Might be worth using Lum to focus and then use offsets, since the nebulosity will be less dominant w.r.t. the star intensity.