Out of curiosity, I did a bit of free lensing using the Nikon G - μ43 Speedbooster with lenses that have a shorter register distance than Nikon just to see what works. Here's a fun fact: High Grade Olympus Four Thirds lenses have a large enough image circle to be used with the speedbooster without vignetting. Or, at least one does: the 50-200mm SWD. At 50mm f/2.8 (SB = 35mm f/2): With the short register distance, this is the farthest away I could focus at 50mm, but as you can see, vignetting isn't a problem at all. At 200mm f/3.5 (SB = 142mm f/2.5): Again, no vignetting problems here either. At this focal length, I could focus several meters. Both images are very sharp, too. So now I'm wondering...would a 25-70mm f/1.4 (35-100 f/2) be possible?