DA* 50-135 comparison

What are we supposed to be looking at here? Reflections of the lamp posts, or the lamps? Are you talking about the curve of light splodges (for want of a better word) on the ground next to the person in the frame?

If so, what's its significance. Sorry if I'm being dense.

Fair comment George.

It usually takes a while to get to know a lens and really be sure it's doing the job. Favourite lenses are held onto very firmly, less good ones reveal themselves in time and get discarded.

It's a tough world for a lens.

Not disputing this, but...

This is all very well, but they're all virtually impossible to compare with other lenses, or even reproducibly with the same lens, since conditions vary from one moment to the next, as you indeed pointed out to me when we were talking about comparing my 400mm lenses (which I haven't forgotten).

I think it's very important to know whether a lens is sharp or not, and at which apertures. Otherwise it's back to all this mystical subjectivity, and it's impossible to distinguish whether the Emperor has clothes on or not.

I thought that's what you were getting at, but it isn't really mystical. It's just a very complex subject and in photography we are talking about a creative process that requires certain characteristics from lenses.

The proof of the pudding is in the final creative image, be it a fine landscape, an emotive portrait or whatever else.

Lens testing can end up as a fruitless process of photographing test charts, maps, or even teddy bears, but in the end all lenses with proper use should these days be sharp. Especially with digital imaging, sharpness is the least of our worries as we have sharpness beyond all 35mm film standards.

As you are clearly interested in getting under the skin of the subject, perhaps this book would be a good start:

The Lens Book by Roger Hicks and Frances Schultz ISBN 0 7153 0149 7 David & Charles 1994.

This explains in a readable way much of what we are talking about.

Fair point, John. I'm sure it isn't intended to be mystical, and what might be very straightforward to evaluate subjectively if you have a lot of experience may very well not be if, like me, you have a lot less experience.

The thing is, we have a lot to contend with. We have the cameras, the lenses, the editing, and the technique, to say nothing of the monitors, and our own eyesight.

Separating all these is not easy, and mostly what I see when people publish so-called test shots I find intensely frustrating, since there's so little attention paid to experimental rigour, and often they prove nothing at all. This drives me nuts, and you're probably detecting some of my frustration coming through. It's certainly not aimed at anyone in particular.

Indeed they certainly should be, especially if you have to lash out £1000 or so to find out. Which is why I wish there was more objectivity in the game.

I completely take your point and George's that there's tons more to it than a bit of pixel-peeping. But pixel-peeping, despite the pejorative use of the term around these parts, is comparatively very easy to do, and it eliminates some of the more obvious problems with the equipment, provided that it's done properly. Which after all, isn't that hard, if you're careful.

Once the pixel-peeping is out of the way, there's no undercurrent of doubt in the capabilities of the equipment, which frees up the mind marvellously to get on with the real job.

Thank you, I'll see if I can track it down. Much appreciated.

I wonder if it is even worth testing. any tests using af would be moot (af can be fooled), manual focus would require precise measurements, (not possible on poorly marked zooms) with specialized equipment like lasers.

I'm refering to testing your lens, to learn it's charactoristics as they apply to your end usage. I'm not partial to side by side, which lens is sharper comparos.

I'd try setting your camera to "mtf" in the settings menu, and run your tests again...I'd be curious to see which aperture setting is sharpest for each lens (as measured by your cameras af system, i recall reading once).
then compare which lens is sharpest at apertures you'd most likely use in your photography....ie, wider for portrait/low light photography, and smaller for landscape photographers....
you may find one lens better suited to your usage than the rest...

Erm, just in case you're not being funny, and I'm being even denser than usual, what setting is this?

Well stated. But, I like animal photography, so long exposures and softness are not the most desired traits in a lens.
Still, I have to say I have taken some photos of my dogs at f/2.8 on the first day and they looked amazing compared to what I'm used to getting.
I think the 50-135 is also sharper at longer focal lengths, which is also normal.

I suppose it is unfair to take some lenses at their extremes and others in their midranges, and expect relevant results. To be fair, I would probably need to take enough photos to create a MTF chart for each. (I'll leave that to some lab techs with the proper equipment - the camera's auto focus and the off camera flash just wont cut it for that sort of quality control).

I generally leave the camera in MTF program mode, unless I am doing sports or other particular photography. Although I don't know if it really makes a difference or if it is one of those eye-candy make-ya-feel-good sort of things like the dust removal system.

The camera selects the optimum aperture for the lens in use. This really implies that we use Pentax lenses, the information for which will be recognised by the camera.

Ah, found it.

Well well. Another little gem buried in the custom menu whose function I hadn't appreciated.

Thanks chaps.

On order from a supplier in the Amazon market place.

I nearly passed out when I saw the new price of the book, but one of them had one, allegedly in good nick, for 7 quid.

Worth a punt, at that price. Thanks again.

Well I've received the book, now. It's in quite good condition - the dust cover is a bit battered, and the corners a bit bent, but apart from that it's fine.

But £6.99 is a steal, especially since the prices on the Amazon marketplace now range from £64 to £117 - and that's second hand, not new.

Any idea why it's so expensive? It was only £15.99 new...

Anyway, it looks very interesting, and I'm looking forward to reading it. Thanks again for the recommendation, John.

Wow, think I might go and pinch the one they've got at Chelmsford library!

Dan