I've found that all the AF bodies I've tried from all manufacturers lock on and focus fast enough. Ironically, the slowest was the Nikon D300S, but maybe it was the lens itself that didn't help.

Contacts build up a deposit of grease/dirt from the environment, so a periodic clean with a soft cloth is a good idea.

Too small a sample Algi, and from a skewed sample as well. Skewed in that it was self-selecting.

Statistics have to be handled very carefully to be meaningful.

I have lots of lenses of choice and it would be a bit misleading really.

For example, I like the 70mm f2.4 very much. That's a combination of it being an excellent lens with beautiful rendering for portraits and being just the right focal length. If you consider than on film my choice was the 100mm then it's not surprising that it suits.

But it might not suit you. You might prefer something longer or shorter for portraits.

Choose in terms of function, not performance graphs. Stick with Pentax branded lenses wherever possible. You won't go far wrong, but you might tweak your choice as time goes by and your photographic style develops.

There used to be an advert about keeping a bank manager in the wardrobe. I could be hired, but the price for 24 hour cover on lenses would be extremely high!

There may be some "good graphs" but, as always, how accurate they are will depend upon the source of the information. There are some very wild figures bandied about and I doubt very much that any lens from any manufacturer has a 50% failure rate.

Read the reviews on ePHOTOzine and you'll see the info, many of the Pentax lenses covered by myself.

I'm currently enjoying the 18-135mm, liking very much its "wiry" crisp look, which is a consequence of relatively high MTF20 values. The clincher for this is silent and fast DC autofocus, very close focusing and weather resistance. I knew it would suit me when I tested it. I also knew that those who look only at performance graphs would not be happy in theory!

Lenses have character and matching that character with our own particular requirements is part of the trick. In terms of technical performance the whole of the Pentax range currently on offer is excellent. The chaqracter of certain lenses will suit some more than others.

Sure, but the question that tantalises is, which lens?

Do you feel you need something wider (you might if you do architectural interiors) or do you feel you need to pull in more distant objects (such as in bird photography) or do you feel you want to get closer (macro lens?).

If you feel it's the upgrade in quality you are looking for, and you like your prime lens, then go for another prime. But the same questions apply. Wide angle - 21mm or even 15mm Limited lenses? Telephoto - a great selection from 70mm, through 77mm, 100mm Macro, 200mm and 300mm.

Narrow down the application and you'll have the answer.

MattyH, you sound as though you are starting to be dazzled by the wider array of possibilities.

I usually suggest starting simply, perhaps with the kit lens, and then after a while it will become apparent whether you need something wider, longer, focusing closer, etc. Something will limit what you want to do and there is the clue as to which lens you need next.

Polarisers on wide angle lenses tend not to work too well. Such a large expanse of sky is taken in that the degree of polarisation varies across the frame. This leads to bands of different shade.

I have always found that the slight natural vignetting of ultra-wides is enough, maybe combined with a small amount of under-exposure and maybe some post processing in Photoshop where needed.