Originally Posted by rparmar
The first thing to know is that all numbers on lenses are rounded off. A Canon 50mm might in fact be a 52mm when tested. A Vivitar maximum f/2.8 might actually be f/2.9. But Pentax has this odd-ball impulse to correctly label their gear. So one lens might be released as a f/1.8 and the next f/1.9. Any other manufacturer would let the .1 slide for the sake of consistency and marketing.
Second, 50mm is not the true film normal dimension, it's just an approximation that came to be common. Pentax went back to the drawing board for the FA43. Remember it was the first of the Limited line... the photography world had seen nothing like it for SLRs. It is a completely idiosyncratic lens.
My theory with the FA31 is that they set out to design another 28mm... something conspicuously missing from the contemporary lens line-up, you'll note. But when it came out it of the lab it was a 31mm. Shaving off 3mm would have meant compromising the design. So they didn't.
Ditto the FA77, which might have been designed as a 75mm between the 50mm and 100mm. Just guessing now.
question!
why then create a 40mm and a 70mm, such concrete, rounded numbers
throw in the mix the existence of the 85 f1.4, which in light with the 1.8, 1.9 and 1.8 of the 3 "limiteds" seems rather dubious.
pentax is a weird company
