Originally posted by JinDesu Because pentax is weird (21, 31, 43, 55, 77)
Consider FF FOV equivalents:
APS-C . 135/FF
--------------
21mm -- 31.5mm
31mm -- 46.5mm
43mm -- 64.5mm
55mm -- 82.5mm
77mm -- 115.5mm
Thinking outside the box?
A couple make traditional sense. 31mm is close to APS-C 'normal' and 43mm is dead-on 135/FF normal. 55mm is dead-on for APS-C portraiture. The rest... don't reproduce the same old formulae, don't fit in the usual slots.
But maybe that's an incomplete picture. Here are the current Pentax primes AFAIK, with FF FOV equivalents:
DA14/2.8 ---------- 21mm
DA15/4 Ltd -------- 22.5mm
DA21/3.2 Ltd ------ 31.5mm
FA31/1.8 Ltd ------ 45.6mm
FA35/2 ------------ 52.5mm
DA35/2.4
DA35/2.8 Ltd Macro
DA40/2.8 Ltd ------ 60mm
FA43/1.9 Ltd ------ 64.5mm
FA50/1.4 ---------- 75mm
DFA50/2.8 Macro
DA*55/1.4 --------- 82.5mm
DA70/2.4 Ltd ------ 105mm
FA77/1.8 Ltd ------ 115.5mm
DFA100/2.8 WR Macro 150mm
DA*200/2.8 -------- 300mm
DA*300/4 ---------- 450mm
Notice the clusters around 14-15 (ultrawide), 31-35 (long-normal), 40-43 (midrange), 50-55 (short-portrait), 70-77 (long-portrait), and the macros. No, it's not a complete lineup -- but certainly an *interesting* lineup. Is their a method to their madness?