Originally posted by ixian Our Limiteds tend to have a bit untypical focal lengths... I would rather expect something like 110mm or 127 or whatever, but definitely not a 'classic' 135mm
Pentax does the 43- or 31- or 77mm thing not because they design the lenses to have exactly those focal lengths, but as a show of...well, I 'suppose you could call it either attention to detail or honesty.
Few of any lenses ever made, by any manufacturer, are exactly the focal length it says on the filter ring. Most are off, some way off. Differences of up to two millimetres, sometimes even more.
Put it another way, if the 43mm wasn't Limited, I bet Pentax just would've called it a 45mm. Although I do suspect this one
was actually designed to be 43mm, since that's the perfect normal lens for a 35mm frame. I'm guessing Pentax decided, retroactively, it's a pretty mark of distinction.
The 31mm would've been labeled a 28, the 77 a 75. The wider-angled DA Limiteds available are probably all pretty accurately named, except maybe the 40 (old design) and the 35 (not Pentax's design...though it'd be interesting to find out if I'm wrong.) Wide angle lenses are normally given the proper focal length; at the wide end a millimetre can make a real difference. And anyway, most of them conform to the standard "multiples of five" rule, save the 21 (a common length, sort of,) which really only seems to matter with lenses over 28mm, funnily enough.
So, what Pentax has done, and will continue to do with this 135mm prime if they make it, is probably just put something like "telephoto lens, about 135mm" on the spec sheet, and then make the best possible lens for the criteria, within the ballpark of 135mm. Might be 130, might be 141, might be 128.
Then again, all makers do this, but only Pentax labels them as correctly.