Originally posted by dms Some of the A lenses carried over the M formulas.
The M28/2.8 is like that, but in some other cases,
like the 24/2.8 and 50/1.2,
the A lenses took the K lens formula
(although the coatings have been said to be improved),
and there never was an M version with those focal length/aperture combinations.
Originally posted by dms For some of the very wide angle lenses (>/= 20mm), . . . the latter formulations are better--although that is debatable for certain lenses (e.g., the 15mm f3.5).
I own, and use, three 20's
(it's a favorite walk-around focal length for me):
the S-T 20/4.5, the M20/4, and the A20/2.8.
Each has its own strengths and weaknesses,
although technically the A20/2.8 is indeed better
(same formula as the FA 20/2.8).
Originally posted by dms Anyway for primes usually the K are considered better, then A
For the 24/2.8, where the K and A share the same formula,
the coatings in the A seem to be an improvement.
For the 50/1.2, the same seems to be true,
although some users do prefer the K to the A.
Originally posted by dms then M (but again there are exceptions--e.g., the 50mm f1.4 is I believe reputed to be better with the A/FA) .
Since I do a lot of shooting at infinity,
I've found the M, with its flatter cemented join,
to give excellent performance.
Other users, who work more at short range,
prefer the K or A formulas with more curvature at that join.