Originally posted by jersey It is 30,5mm
Close, but not the same. Well, APS-C is special so I will live with difficulties coming with it :P
Rounding matters if we are splitting hairs. Apsc crop ratio on Pentax is more like 1.52 than 1.5 making it just over 31mm equivalence. But a more precise metric is available: Field of view.
DA 21
Field of View (Diag. / Horiz.)
APS-C:
68 ° / 59 ° FA 35
Field of View (Diag. / Horiz.)
Full frame:
63 ° / 54 ° FA 31
Field of View (Diag. / Horiz.)
Full frame:
70 ° / 60 °
So clearly the DA 21 on apsc is not as narrow as the FA 35 on FF. However, it has a tad narrower field of view on apsc than the FA 31 would on ff. It’s quite close to the same perspective but slightly narrower and this is in line with the 1.52x calculation of 31.92mm equivalence.