Originally posted by NaClH2O To be truthful, I'm not sold on the idea that a lens body has to be metal. Several of my favorite lenses have carbonite or other composit barrels. One of the benefits is that they are much more stable in the cold and are also lighter. The FA 20mm F2.8 has a "plastic" barrel, and it is one of the highest rated lenses in the Forum database. Same is true of the legendary Tamron 90mm F2.8 macro. In these days of sophisticated composits, I see nothing wrong in a 'plastic' body.
NaCl(it's the care put into the design and assembly, not the material)H2O
Interesting that you raise the FA20, as I think the FA20 is to the DA21 what the FA31 is to the FA35. I have certainly seen many more impressive photos from the 31 and 20, but then again, the most accomplished photographers posted those photos. I'm not sure if it's the lens or the photographer (or the processing) that gives these photos their magic.
Also, with both lens pairs, the 'lesser' lens tends to score better on objective tests (Photozone, eg.). I know line pair resolution does not communicate the character of a lens, but there is some irony in the price differential. Precision can hurt a lens.
I must say I benefit from the premium the 'elite' Pentax lenses cost. Just as the DA21 prices stay more in check vis a vis the elusive FA20, the FA35 price is lower because it is the 'Queen's' ugly stepsister.