Like Marc I have little interest in manual zooms; besides his reasons I don't want to carry a heavy lens. Ever. Besides, on digital a lot of the focal length ranges no longer make much sense to me.
Where I want a zoom is in the super-wide end, since a small focal length change makes a big difference and I'm not going to carry primes for every number from 12 to 24, even if that were possible. And of course the whole "just move if you don't have everything in the frame" makes no sense if an inside wall is behind you. So that explains why I have the DA12-24mm.
I have the DA55-300mm because I have little dedicated interest in telephoto. This lens covers a big range well while staying light in the bag. I can't think of an old lens that would be any better.
That's it for zooms though; otherwise I prefer primes. (I do own other zooms but don't find myself using them.)
I must say that the inability of assigning a dial to ISO in manual mode often kills my enjoyment of using manual primes. I sure wish Pentax would notice me complaining about this and issue a simple firmware fix. I want the same dials to do the same thing no matter what mode I'm in and what type of lens is on the camera. Aperture control is on the lens so shutter and ISO should be on the dials.
The other thing that gets in the way of usability is the metering problem. It's one thing to press the green button before a shot. It's another to press the green button, then compensate for the exposure, then take the shot. That's tedious and too slow.
I think that besides price the main appeal of older lenses is in their solid metal build and smooth manual focusing. Digital-only lenses simply don't have that feeling; the focus must turn freely to allow the motor to drive the lens. However I think the FA Limiteds are on the good side of the MF fence.
MF lenses I use include the Vivitar 24/2, Vivitar 28/2, Vivitar Series 1 105/2.5 and smc Pentax 50/1.2.
Please, Pentax, fix the two problems noted above so I can enjoy MF and manual aperture lenses as much as I should.
Oh yeah, my
last two blog articles are about choosing lenses.