The recently announced Fujifilm XF 8mm F3.5 R WR is the widest rectilinear prime lens for the X mount and the only other Fujifilm X mount lens that goes as wide is the XF 8-16mm F2.8 R LM WR but it comes with a huge size and weight disadvantage. Below is the scaled size comparison of these two and the Fujifilm XF 10-24mm F4 R OIS WR to better understand how these compare in real life, followed by a specs comparison:
Fujifilm XF 8-16mm F2.8 R LM WR vs Fujifilm XF 10-24mm F4 R WR vs Fujifilm XF 8mm F3.5 WR
As seen on the image, the new XF 8mm is significantly more compact and lighter than the other two, but lacks the focal flexibility of the zooms. I personally use my wideangle zoom lenses at the widest end most of the time so the more compact and affordable 8mm prime would be my choice if I had to choose between these three.
Fujifilm XF 8mm F3.5 WR vs XF 8-16mm F2.8 R LM WR vs XF 10-24mm F4 R WR Feature Comparison
