Originally posted by Lowell Goudge WHere small does get me a little, is in the limits it imposes on maximum aperture. in the transition from K-M series lenses, we lost some significant lenses.
specifically,
- the 500/4.5 disappeared totally
- the fastest 50mm went from 1.2 to 1.4
- the 85mm went from 1.8 to 2
- the 135F2.5 disappeared
- the 200 F2.5 disappeared
- oddly enough the 150 went from F4 to F3.5
While it's true that the K 85/1.8 was replaced by the slightly slower M 85/2, none of the other fast lenses mentioned above disappeared when the M series came out. The K 200/2.5 actually came out in 1977, the same year as most of the M lenses. It remained in production until 1986. The K 135/2.5 remained in production until 1985, which means it was not replaced by the slower M 135/3.5, but by the faster A 135/1.8. The K 50/1.2 remained in production until it was replaced by the A 50/1.2. The K 500/4.5 remained in production until the late 90s. The M series did not completely replace all the original K-mount lenses; most of the fast high-end lenses remained in production until the A series (or even later).
The DA limiteds are small because that is the lineage of the limiteds: the original FA 43 was designed to be small, which it is for FF lens. It's also f1.9, which is slow for a 43mm lens. The small size was probably originally pursued partly as a selling point, but also to keep the cost down. When the lens sold well, Pentax decided to make more. All but the FA 31 were designed to be small, thereby sacrificing the maximum aperture but keeping costs down. Even the FA 31 was originally supposed to be a smaller, slower lens (I believe it was supposed to be f2.4), but Pentax decided for utterly mysterious reasons to make it their fastest wide angle lens ever. It's the largest and (no coincidence) the most expensive limited.
So, at least in terms of small primes, I think keeping costs down plays an important factor. A DA 21/1.4 produced with the specifications of a limited lens would be a very expensive lens. Since its move to digital, Pentax has shied away from producing lenses more expensive than $1,500, while trying to keep most of their lenses under $1,000. This means high end primes have to be a bit on the slow side to keep the prices down. And if you have to make the lens slow, why not also make it small?