Hans K Aspenberg

Just tested my old venerable Vivitar 55/2.8 through a no-brand Chinese 0.72 reducer. Brilliant lens and even better through this reducer than using it directly via an regular mount adapter.
 

 
Processed from raw in LR CC 2015.1

Just tested my old venerable Vivitar 55/2.8 through a no-brand Chinese 0.72 reducer. Brilliant lens and even better through this reducer than using it directly via an regular mount adapter.
 

 
Processed from raw in LR CC 2015.1

From my observations when I tried this lens about a year ago it is as sharp as the XF14 (or a tad better) in the inner half of the image circle, but then it deteriorates towards the corners which never become 100% sharp dependless of the aperture. As I wrote above, and in several others online-fora, this is a limitation caused by the steep angle of the light rays when they hit the sensor in the corners. Actually not the sensor itself, but the 1mm thick filter stack situated about 2.5 mm in front of the sensor. If you look at a digital Leica you will see that it has a extremely thin filter stack to be able to use these older symmetric lens designs. (The original M8 didn't even have a IR-blocking filter at all which caused a lot of havoc back then.) The new SONYs are even worse off than the Fuji-X due to an even thicker filter stack.
 
Look up: http://www.fujirumors.com/the-performance-of-carl-zeiss-leica-m-lenses-on-the-fujifilm-x-pro-1-by-jan-vogelaar/
 
Newer, retrofocus designs for the M-mount will usually work very well, but then these will be as large as the corresponding XF-lenses.
 
;-D Hans

Just tested my old venerable Vivitar 55/2.8 through a no-brand Chinese 0.72 reducer. Brilliant lens and even better through this reducer than using it directly via an regular mount adapter.
 

 
Processed from raw in LR CC 2015.1

Just tested my old venerable Vivitar 55/2.8 through a no-brand Chinese 0.72 reducer. Brilliant lens and even better through this reducer than using it directly via an regular mount adapter.
 

 
Processed from raw in LR CC 2015.1

Just tested my old venerable Vivitar 55/2.8 through a no-brand Chinese 0.72 reducer. Brilliant lens and even better through this reducer than using it directly via an regular mount adapter.
 

 
Processed from raw in LR CC 2015.1

In my opinion, the XF14 is about perfect. Sharp across the field, little vignetting, no distortion.