Would you add the 100mm F2.8 macro WR to the "safe" list? The lens barrel does extend for focusing of course, but the rear glass element is fixed.

Right, so the problem is price, I think I see it now. Perhaps it's a £200-ish lens that costs £350, so it's just overpriced in terms of absolute image quality? I think that's why I went for the DA55-300 (discounted to £245), anyway. For £199, or even £245, I might have chosen the 18-135WR. Of course, for some people, the extra money may be worth it because it has other worthwhile benefits, the edge quality at the telephoto end not being a deal breaker.

One thing that has puzzled me about the photozone resolution tests is what effect will they have on less than 100% photos, if say resized to 50% or less. That, I suspect, is what happens when we print at least 99% of photos, for most of us.

K5 manual suggests that the optimal paper sizes for 100% (16MP) is A2 or 14x17, and for about half size (6MP) as A4 or 8 x 10.

Well, at F8, the centre resolution measured by photozone on the 18-135 is very good to excellent at 135mm (the worst focal length), at 2373 (LW/PH). Presumably that kind of resolution would be good for an A2 print at optimal quality. The 'borders' resolution is about half that figure, so presumably would be good for an A4 print at optimal quality.

Does this mean that for A4 prints and below, the entire print right down to the borders would be of optimal quality? In other words, that for A4 and smaller, the poor measured 'border' quality is irrelevant? And that even then, it would only be an issue for the type of print that needs sharp edges, or where we don't want to crop out the vaguely central area.

This makes me wonder how much the photozone results actually relate to real World viewing and printing of (most of) our photos. Perhaps, I suspect, not very much?

Only just noticed this thread.

A few years ago, I had the exact same problem with mt istDL2 as you did, I tried everything but eventually, as it was well out of warranty, I gave up. I am convinced that there was some kind of electronics failure within the camera, nothing to do with the contacts or the batteries themselves.

I replaced it with a K100D super body, (but still have the istD, which looks rather sad after all this time.)

Thank you John, I can see that now. We have to move back with our APS-C SLR to get all of the subject in the frame, compared to an old full frame SLR camera using the same lens. Therefore, because we are further away, the perspective distortion will be less. I think that's it.

Can we use the crop factor when estimating pespective distortion? Or is it 50mm = 50mm = 50mm, whatever the crop factor?

Just wondering.

Leaving aside the colour balance differences, doing A/B comparisons of the crops in PSP (after exactly matching the sizes and rotation), confirms my initial impression that the top crop (K5) is both sharper and less noisy. Look at the top and bottom of the eyes, for example. However, the sides of the eyes are slightly sharper on the 50D (but the difference is less than the difference vertically, I'd say). The mouth top and bottom edges look sharper on the K5 too.

So if it's down to focus, I'd say the K5 focused marginally better - but I wonder if there is an element of slight camera shake too?

I coveted then bought the 100mm F2.8 DFA macro WR this month when Jessops listed it at a crazy price - the plan is to force myself always to carry it with my K5, because it's my only WR lens, my only macro, is my brightest AF lens and my sharpest too.

So far, so good - but it's early days!

Photozone appear to have pulled all the test charts from their review of the 18-135WR, the comments only remain (currently).

http://www.photozone.de/pentax/597-pentax_18135_3556?start=1

I have checked some other Pentax lens reviews there and they seem to be complete, with test charts. Hmmm...

This gave me a good opportunity to pin down the exact AF fine focus setting for my new 100mm lens, it ended up as -8 and then, under normal domestic tungsten lights, using a tape measure on the floor and a very small adjacent target, it focuses perfectly every time. The only lens I can't quite get enough focus adjust on is an old manual M/200 (for CIF use). Seems to focus pretty consistently too indoors and out, so I am puzzled by your issues. I don't have any AF lenses wider than F2.8 though.

I always use centre spot focusing, which might be relevant.