In a nutshell, because a lot has already been described above. I compared the approximately 5 times as expensive (and heavy) Zeiss 85 f 1.4 on my SLT 99 with this mini lens on the Nex 6. Test scene: Roof front of the neighboring houses about 100m away, camera tilted by 45 degrees, so that the front goes from corner to corner. Workflow: Tripod, shutter release delay 2 seconds, stabilization switched off, aperture priority, ISO Auto, shots in RAW (internal corrections switched off), in Lightroom, default setting "developed", lossless downscaling of the 24MP image from the SLT 99 to 16MP in a TIFF file around the Comparison on the screen at 100% view for the 85 not to make it unfair. Shooting at f/1.4; 1.7; 2.4; 5.6;8 and 13 for the 85, 1.8; 2.5;5.6 ; 8 and 13 on the 50's Nex. Result in terms of sharpness: I didn't want to believe it, I repeated the test twice: There is a better lens than my 85, which was previously classified as superlative. Up to an aperture of 5.6, the 50 is clearly sharper in all comparable apertures, both in the center and in the corners. The 85 lags behind by about 1 to 2 f-stops and only achieves with an aperture of 5.6 what the 50 can already do with an aperture of 2.5. At aperture 8 and above, both lenses pull the same. So if you don't necessarily need the considerably larger exposure potential of the full format and the aperture 1.4, the 50 Nex is the best choice. PS: without downward scaling, the purely visual result is even more desolate for the 85.