Erik van Straten
Veteran
Nope.
I use the Summar at f/2 with the FISON all the time with no vignetting.
I just looked through my Lightroom library to find shots definitely taken at f/2, and this one is a good example:
...because it was taken moments before I swapped to the 50/1.9 Serenar I'd just picked up - which was also wide open and didn't have a hood on:
There's surprisingly little difference in rendering - and, most notably, possible vignetting.
The one time the FISON has ever caused any issue at f/2 was when I put a filter behind it:
When you compare both shots you'll see that the Summar shot has dark corners, not small dark spots in the extreme corners, but larger parts of the picture towards the corners. These are caused by the FISON. This is what I ment to say above, but I was occupied with other things at that moment so I forgot to explain exactly what I wanted to say. I hope you'll see this addition.
Erik.