Lens options for the *ist-DS

[David Oswald]

Setting aside the distinctions between DA, D-FA, FA, F, A, M, and basic 
K lenses, I wanted to discuss focal lengths for the *ist-DS.

I've got my zoom kit pretty much where I want it for now:
    SMC Pentax-DA 16-45mm f/4 ED AL
    SMC Pentax-FA 28-105mm f/3.2-4.5 IF AL
    SMC Pentax-FA 80-320mm f/4.5-5.6
Now I'm working on building my fixed focal length kit.  Currently it 
consists only of the SMC Pentax-FA 50mm f/1.4.

I love that lens; its focal length is great as a mild telephoto, very 
nice for portraits.  And its so small, yields a bright viewfinder, and 
offers fast optics.  Imagine buying an f/1.4 telephoto lens this size 
for a 35mm camera!

That leaves me with some holes though: Wide, Standard, and longer telephoto.
I think I've settled on what to work on accumulating: a 35mm f/2, a 
135mm f/2.8, and a 20mm f/2.8.  This still leaves me with a gap between 
50mm and 135mm, but currently there's just nothing in the Pentax 
assortment I can afford at, say, around 85mm, unless I go for an M lens, 
and even those are not cheap... so I'll live with the gap for now.

But then along comes the SMC Pentax-DA 40mm f/2.8 Ltd.  This looks like 
an interesting lens.  Its pros are: Compactness, great image quality, 
great bokeh, solid construction. Its cons are: wide open is only f/2.8, 
and it doesn't seem to fit into any particular suite of lenses.

Is this a lens worth owning instead of my 50mm f/1.4?  Or is it an 
"instead of the 35mm f/2"?  I don't see its niche.

Dave