Originally posted by Shakey I was considering upgrading if there were two different lenses.
If you are considering upgrading from the 18-135, there are several possibilities, each with its own merits and drawbacks:
- HD Pentax-DA 16-85mm F3.5-5.6 ED DC WR: You gain 2mm at the wide and and it is said to have better image quality, but it is also more expensive, a bit heavier, a bit bigger, and it only goes to 85mm. So if you value the long end of your 18-135, this is not the one lens for you. You could of course combine this lens or any of the following with a tele lens like the HD Pentax-DA 55-300mm F4.5-6.3 ED PLM WR RE, but you'd still have to change lenses to go from wide/normal to longer tele. If that would be possible for the type of shooting you do, you could consider this. If not, I guess you're "stuck" with the 18-135 (not that that'd be a bad thing). There is a SMC Pentax-DA 18-270mm F3.5-6.3 ED SDM (and an older, discontinued 18-250) but I never see that one recommended, I guess because it combines all the disadvantages that come with it just to enable that big of a zoom factor in a single lens.
- Another option would be a SMC Pentax-DA* 16-50mm F2.8 ED AL [IF] SDM, which gives you a maximum aperture of 2.8 throughout the zoom range, but there are some other limitations with it that make me not really recommend it: the SDM focussing motor could fail if not used regularly (?), and at the price performance ratio it gets good contest from the third party lenses 17-50/2.8 from Sigma and Tamron. Those don't offer WR like the Pentax lens does, but they are much more affordable, while not being worse all around than the Pentax 16-50.
- Another, even more limited lens (in more than one meaning of the word limited) would be the HD Pentax-DA 20-40mm F2.8-4 Limited DC WR. Not that big of a zoom range, but it offers you the Limited lens series haptics, optics (and/or rather looks?) and performance. You'd have to pair it with a wider lens as well though, if you value focal lengths wider than 20mm. An option for that would be the HD Pentax-DA 15mm F4 ED AL Limited (though many folks here like the older SMC Pentax-DA 15mm F4 ED AL Limited for the nicer starbursts it can produce), which would be an excellent match for the 20-40.
- One more possibility would be the older SMC Pentax-DA 16-45mm F4. It would offer a little more room on the wider end than the 18-135, but I don't know how the image quality in overlapping focal lengths compares. It may be available on the used market for around $100 or less, though, so that might be a cheap way to go wider than 18mm.
All that said, I like my 18-135 as a great single-lens walkaround solution, for when I don't know what I might see on the way, when the weather may turn bad and when I can't or don't want to take more than one lens with me. I still lust after the 16-85 sometimes, but I'm not willing to buy it new for the price it sells and I've not yet found a used offer for a fair price in my vicinity yet.