Fixed or zoom?

Overwhelmed with good advice. But it's a good feeling: I have plenty to investigate. I do like the size/weight of the K5 and I don't want to encumber it with an overlarge/heavy zoom. I worry more than a bit (as Womble above) about ending up with a good lens - say, a 50-135 - and yet finding myself leaving it at home because of its bulk, and perhaps because it doesn't quite offer all the focal lengths I like to use. After some research into the suggestions above, I feel a trip to SRS coming on: trying out a few lenses literally for size may help clinch it. V grateful to you all.

Pentax 16-45. Worth a look.

Dave

If you want something with a shorter focal length and less weight than the 50-135mm (and I must admit that lens is certainly on the bulky side) the I would probably go for the Pentax 17-70mm.

Unfortunately the 2 I tried both had focus problems between 50-70mm and I didn't like the "workaround".

You could get an 18-55mm WR lens... they're very lightweight. Not perhaps the best IQ in the world, but you can complement it with your two primes when quality really counts, and maybe add the DA35mm f2.4 as well. Those two lenses would also be cheaper than something like the 17-70mm (let alone the DA*16-50)....

With the right post-processing, it can be very hard to distinguish between a prime and zoom, certainly on the web.

I've been using primes a good deal more since I bought the three FA Limited lenses, but it's the 77mm that I really love. Funnily enough, the 70mm DA Limited also enchanted me. So is it the focal length as much as the quality?

Even the 18-55mm can look lovely and crisp at f11 and web resolution.

I'd also recommend the Tamron 17-50. I have both this and the DA17-70. While I've been very happy with the DA's performance over the last couple of years, I got the Tamron recently because I wanted f2.8, both for low light and to throw b/g's (which was often frustrating with the DA). I also thought as it had gone under £300 it was very good value, and got one with a view to comparing it with the DA and selling one on.

On the evidence so far (only had it a month or so), it is a very sharp lens - sharper than the DA, though I have no complaints about the DA. Colours are different, perhaps not quite as nice as Pentax ones but nothing to worry about and easily adjusted (if so desired). Bokeh was very nice on the DA, haven't really tested this much on the Tamron yet as I have used it mostly at a wide angle, but on the few longer shots wide open I have the Tammy looks good too. The extra stop I find very useful - I use it wide open a lot of the time and it performs well (though go down 1 or 2 stops and it's even better). Also, it's smaller than the DA - both in weight and dimensions. For an f2.8 zoom it's remarkably small - miles smaller than the DA*16-50 (77mm filters:shock, the size of which I find quite offputting.

The DA does have a nicer build and the extra 20mm is very useful. But I think it will be this, not the Tamron, that I sell on my next trip to the UK.