<<Metabones Speedbooster Ultra: the one to beat. Unfortunately, the one to beat
<<on price, as well.
Should at least look at the Speedbooster M43 XL version which is 0.64X and gets
the crop factor down to 1.28 X vs 1.42X with the ultra. Unfortunately it is
not recommended for use with E-M1 Mk2. Bah.
The MTF of most lenses actually IMPROVE with either, the way these things work
though more so with the Ultra at the price of more crop factor.
Themed Olympus Photo Exhibition: http://www.tope.nl/