Re: M-20/4 vs. K-24/2.8 ?

[Arnold Stark]

whickersworld schrieb: > The 24mm f/2.8 Nikkors are effectively 
distortion-free.

" effectively distortion free" is a nice expression effectively meaning 
either "distortion is still greater than 0" or "the distortion did not 
spoil any of my pictures". In these senses, the A20/f2.8 as well as the 
K24/f2.8 could be called distortion-free, too. However, the M20/f4 is 
not " effectively distortion free" as for me it did indeed produce some 
ugly distortion with the horizon near the upper image border.

However, if one systematically MEASURES distortion (i.e. the bending of 
straight lines), there is no super-wide angle lens that I know of  that 
really is distortion-free.
For example, in 2001 German Color Foto tested 15 lenses of all major 
brands (including FA24/f2, FA20/f2.8, ands also the Nikkor 24/f2.8) with 
focal length between 19 and 24mm. No lens collected more than 5 points 
out of 10 for its distortion performance (with Leica and Zeiss 
performing best).
Here is some test results on Pentax lenses from Chasseur d'images:   
FA20/f2.8: 0.5% barrel distortion; FA24/f2: 0.4% barrel distortion; 
A24/f2.8:  0.5% barrel distortion.

Arnold