vignetting of the 75% ray

Hi Folks

I need some help with planning my 12" F5 dob.
I ran Newt to get dimensions for the scope and no matter what I do I am left with vignetting of the 75% ray at the focuser. I have a 2" focuser with a 1.25" adapter. When I use the inner diameter of 1.25" I get vignetting of the 75% ray, but when I run newt with the 2" focuser diameter there is no vignetting. I have a 302 mm F5 primary and a 63mm secondary

My question is: How much will vignetting of the 75% ray effect my images at the eyepiece.

Any help would be greatly appreciated.

Just a quick look Trevor but from what I see, I think that the 75% illuminated mirror equates to a field of view of over 1.5 degrees. To achieve this with your mirrors would require a 45mm focal length eyepiece (with a AFOV of 52degrees) or a 30mm with a 80 degree AFOV. Eyepieces of this spec are expensive and will be 2" barrels anyway. Hence I think (imho) that you will be fine.