Vignetting question: 383L+ 1.25 filters at f/4?

[dokeeffe]

Hi,

I have read that the EFW2 is good to f/5 when using the 383L+. But how bad will vignetting be it be at f/4? Anyone have any examples or flat frames?

I'm currently using my Atik 383L+ EFW2 wheel and baader 1.25" filters with an 11"SCT scope at f6.3.
All working well.

However I'm contemplating changing to a much smaller scope with an ~800mm focal length..

So I have in mind a 6"f/5 newtonian or an 8"f/4 (with coma correctors).
I see someone posted a sample image here comparing f/5 and f/4 but with a filter 'drawer'
https://stargazerslounge.com/topic/207351-have-i-made-the-right-choice-of-ccd/#comment-2205633
Going by this then it should be easy to correct with flats.

Would like to see if anyone else out there is using this setup at f/4

Thanks,
Derek

[dokeeffe]

Update,
I found someone using a 383L+ with 1.25 filters at f4 and seems to get very good results.
flat field image posted here > http://www.davidlloydjones.com/ancillary-imaging-equipment.html
Derek