[shaolen]

Can someone take identical photos with identical focal lengths of each of these three series lenses and post them? I'd like to see the different characteristics if any.

[UncleVanya]

I have an m and an a 50 f/2,not very exciting.

[lytrytyr]

The optical designs often changed,
so I don't think you can attribute many different characteristics to the series as such.

The 20mm lenses are clearly quite distinct,
but even the 50/1.4s have subtle variations, like in the curvature of the cemented join.
There, the M might look better towards infinity, but the A and K are often preferred for closer work.within a series

Where you do have the same design, like in the K and A 50/1.2s,
sample variation within a series may be a significant factor.

I do have both K and A versions of the 24/2.8, same optical design,
and there the coatings on the A may be slightly better.

[Lowell Goudge]

What focal length?

[bassek]

M and A were optically of similar design, whereas the K was not always (50mm other than f/1.2).
Sometimes you see a different tint on the glass for the same lens.

Summary: sample variation is far more determing than the series as lytrytyr said.

Seb