Originally posted by MXLX is there a good reason to "upgrade?"
If the only reason to ask is that you've read that another lens is better, then no, there is no good reason to upgrade. The 18-55 is a nice lens, so unless you find it to limit you in any way you should probably stick with it for a while longer.
That said, a lot of us don't need a
good reason to upgrade - we'll jump at any reason
A lot of lenses will be better than the 18-55, but "better" usually comes at a cost - and sometimes for very little return. E.g. if your current lens is sharp enough you will gain little from an even sharper lens. If you mainly shoot landscapes you will probably not use the wider aperture of a faster lens much.
Some alternatives, and the way I look at them:
- Sigma/Tamron 17-50/2.8: Sharper and with wider max aperture. The Tamron lacks an internal focus motor (like the 18-55) if that's of importance to you.
- Pentax 16-50/2.8: Much the same as the above. 16mm is getting usefully wide if you like wide angle.
- Pentax 18-135: Better image quality than the 18-55 and considerably longer reach. A nice allround lens.
- Pentax 16-85: Well known for its image quality, and a very useful zoom range IMO. Probably my pick if I needed an APS-C zoom right now (but it ain't cheap).
- Pentax 20-40: Another very well liked lens, and quite compact. f/2.8 at the wide end. The main downside (IMO) is the limited zoom range.
The downside with them all (to a varying degree) is more bulk and weight - and cost. The least expensive option is probably the Tamron if you can find it.
An alternative could be, as others have suggested, to supplement with a few prime lenses. Your F50/1.7 is an excellent lens, and you could add something like a DA L 35/2.4 if you want something budget friendly that's a bit wider. This will leave you with a decent standard zoom for general use and a few very good primes for "special" cases (typically if you need a wider aperture or ultimate sharpness).
Yet another alternative is to supplement with more range, e.g. the well liked DA 55-300 PLM for more reach, or something on the wide end if that suits you better.
So no, there is no
good reason to upgrade - or supplement - but there are always
reasons