[Alizarine]

Some say the FA43 is the "perfect" FL or something for the 35mm format since it covers the diagonal just right.. just asking, how about APS-C? Which lens is closest to the APS-C diagonal?

[Adam]

43 / 1.5 =~ the FA 31mm

[Alizarine]

43 / 1.5 =~ the FA 31mm

Thanks for the quick answer! And hah, another FA Limited. Another reason to call those three "legendary".

[gtl]

For the price... Sigma 30mm?

[Tonto]

Why the FA 31 is so esteemed, 'standard' on APSC and wide on 135 format and sharp across the frame

[RioRico]

Some numerology: A sensor that is nominally APS-C has a diagonal of 30.1mm. Not all sensors called APS-C are that exact size, however. My K20D has a diagonal of 28.1mm, and my favorite strolling lens is 28mm. I've noted APS-C sensors that range from 25mm to 31mm. I'm not sure of the exact size of the Kx sensor -- that will be in your user's manual.

The AOV (angle of view) difference between 28mm and 31mm is trivial; between 25 and 28mm, is slightly more noticeable; and between 25mm and 31mm is quite distinct. But I'm sure that I could mount 28mm or 29mm or 30mm or 31mm lenses on my K20D and not really notice. (Yes, all those focal lengths have been made.)

Which means that if you find a good deal on an F28/2.8, you could be really happy.

[TOUGEFC]

43mm divide by 1.5 is actually 28mm.

So 28mm then 30mm then 31mm in terms of closeness.

Sigma 30mm f/1.4 is the fastest and the only AF f/1.4 of the bunch which gives you shallow DOF isolation that no other lens in that range can acheive.