So I tried using my SB with my old Nikon primes and hoped that there was enough sensor coverage to keep the VSM at 100% and still take advantage of the extra f-stop. Unfortunately to get rid of the vignette I had to set it to 92%.

Would it be better to use a normal adapter to avoid image scaling and stay at 100%? Or would you have to pixel peep to see the difference between 92% and 100%. I won't be able to do any of my own testing for a few days- but wanted to see what other owners thought until then.

=^_^=

92% sounds pretty good. I expect your speedbooster is only designed to cover a micro four thirds sensor.

If you look at this page: Metabones® (http://www.metabones.com/products/details/MB_SPEF-M43-BT4) you can see that Metabones recommend a setting of 86%.

What SB do you have by the way?

I'm in the market for new lenses and maybe an SB too, but I think that having to set the VSM down to 86% almost negates the SB's affect on the focal length, although the additional light gathering will still be useful.

Duncan.

Rokinon 35mm and 85mm T1.5 primes can handle the 0.7x SpeedBooster at 100% VSM without vignetting.

In that case you'd expect all the Rokinon Full Frame lenses to do the same or similar...
I really think I should buy them.