Originally posted by Optical Illusion Thanks Monochrome... So it doesn't seem like they're different enough to keep both. I see no reason to do that, so which one should I keep? Or are the differences ClassA mentioned significant?
If you will only shoot average distances between f/8 and f/16 then any Pentax normal lens will do a great job.
The differences
can be significant, depending on what you need to use the lens for.
If you need edge-to-edge sharpness at less than f/4 (a "flat" field) the 50/1.7's were specifically designed with that in mind.
If you want nicer oof areas and sharp enough center area below f/4, plus better focusing in dim light and a faster shutter wide-open, then 50/1.4 was specifically designed for these conditions.
If you want classic manual focus feel, the M or even K lenses offer pure, smooth, damped focusing (the Takumars are the best IMHO).
If you want automatic aperture control from the camera, the A lenses have the electrical contacts.
It is all about the compromises you will make to get the best price for the features you need.
Or owning three or four different 50's for different purposes.