Originally posted by PANGU_yien I have to ask the same question. With primes specifically, many people have been touting this idea that a FF or 24mp crop sensor is going to out-resolved all the old Pentax lenses. CA, distortion, AF and whatever else aside... if you're just comparing pure sharpness, I don't see how that's true at all. It seems Adam and the others tested the FA 77 to be sharper than the DA 70. There's a great lens test where the old A*85 1.4 has a slight edge on the newer Canon 85 1.2L. If sharpness is what you're looking for, I think it depends on the lens, but I still don't think any upcoming sensor (FF or crop) is going to out-resolve the good ones for at least a few years. Does anyone have a different perspective on that?
I've been getting excellent results with old primes on my K20D. Yesterday I used an SMC 35/2.0 and a Super Takumar 105/2.8. I was photographing highly detailed subjects at mid apertures, using a tripod. The results are sharp enough for my standard gallery print size, which is 24x36 inches. Detail and sharpness are important parts of my personal style- I get a lot of favourable comments in that regard. I generally work with newer lenses for convenience, but enjoy playing with the old ones occasionally.
My sense is that the pixel density of a 24MP full frame would not be all that different from a 15MP APS-C, so good older lenses should be fine for that format. I can't speculate on how older lenses would hold up with higher pixel density. It may be possible to get a sense of this by looking at how older lenses are faring on other brands' bodies. My next planned camera upgrade will be in one to two years. I expect to rent a couple of bodies and see for myself.
Getting back to the original question, yes, newer lenses are in general somewhat better optically and certainly more convenient to use than older lenses. On the other hand, carefully selected older lenses, for the right price, can be a very good value for some applications. You won't embarrass yourself if you use older lenses well.