Originally posted by leeak There must be something fundamental about these focal lengths. So why are these focal lengths important?
I think it's largely historical accident. I mean, sure, you want something wide angle, something roughly "normal", and something in the short-medium telephoto range for portraits or other purposes. But I don't know that would be any reason to really shoot for those exact focal length eqivalents as opposed to some other wide angle, normal, and short-medium telephoto focal lengths.
With that in mind:
Quote: @ 28mm - We don't have a DA 17.5 and would the DA12-24/4 be a good alternative?
Well, it's a zoom, not a prime, and much larger and more expensive than the 28 was. Unless you feel you *need* a lens that wide, I would think the DA21 would be more comparable to what the 28 was. the recently announced DA15 could turn out to be interesting, too.
Quote: @ 50mm - FA31/1.8 comes close to 50mm
True. It's quite expensive, though, and much larger. You might also consider the FA35/2, or even an M28/2.8, as your "normal" lens.
Quote: @ 135mm - FA85/1.4 comes close but the FA77/1.8 is smaller and cheaper
There is also an M85/2 that is cheaper still. And an M100/2.8 that is even cheaper. If you are thinking primarily portraits, then 100 might be on the long side (more like 150 on film), but the extra length makes it more suitable for many other purposes. If you are thinking about portraits primarily, the DA70 would also be a very good choice.