Originally posted by Uluru
Well, some Ltd designs were based on old lenses.
I don't think so. Most have no direct matches for focal length or max aperture. Even though the 40/2.8 has the same number of elements/groups and max aperture, they're not the same -- different minimum focus distance, and significantly different performance as well.
The FA20-35/4 is a pretty good lens, but performance-wise, still pretty close to the DA16-45 and even 18-55 in the overlapping range. A few years ago I was using it as a compact kit with my old DS2 -- I liked its sort of stubby handling -- but doubt it was much of an improvement over these lenses, and its hood isn't a good match for APS-C. To get the limited tag and have a hope at selling more than a few examples, I think it has to be faster than f/4 (my guess would be f/3.2 or f/3.5), and would have to beat these lenses in performance. I think there are some (including myself) who would be willing to sacrifice max aperture and focal length zoom range for size/weight and performance. I think it might be thought of as a substitute for the primes in this range that Pentax has been thus far reluctant to produce, and reflects a reality where it is difficult to make an exceptional APS-C SLR prime in this rough focal length range (<30mm) that outperforms modern zooms, is faster than those zooms, and remains compact.