JP Solutions is the authorised repair centre for Pentax - follow the details on the Pentax.co.uk website or Google them.

They will quote you for repairing your lens back to its factory state.

I've had a K10D repaired by them and the repair was exemplary, albeit rather slow.

There are a few issues there that are interesting.

Decentering: I've seen decentering figures in the past and even 15% decentering can give good results, depending on the actual lens design. It may be less than the potential, but a great lens decentered 15% will be better potentially than a poor design decentered 2%. It will be worst with complex lenses of course, all other things being equal.

Manual focus: I can't agree that f1.4 lenses are difficult to focus, that one's a complete mystery to me. The limited DOF means that the sharp point snaps in and out beautifully and alo the brighter image makes it easier as well. When you stop down to f8 or whatever, all that's happened is that the focusing has been as accurate as it possibly can be. I think the problem is more that at f1.4 the point of focus is very precise and if the camera wavers to and fro or the subject moves focus will be instantly lost.

Calibrating AF: So far, no need found. Lenses snap visually into correct focus, even close up. Having the option is excellent, although i would have a slight concern that the correct point of focus may vary depending on distance and focal length (in a zoom) so a compromise setting may still be needed. It could be easy for an inexperienced photographer to get this wrong.

I'd take the 55-300mm by choice, compact and excellent.

Weddings are very hard work, so I do them selectively for clients I am sure will be OK. However, I charge a full rate according to distance, time expected and so on. The package is always the same and I make Photo Books, a story of the wedding in pictures in effect. If that appeals, you book, if not then there are other photographers.

I don't do many weddings, nor do I want to. I wouldn't do one for £450 as it's far too much hassle for that.

In Photoshop CS and later, Photo Filters might be an easy route. Just dial in the appropriate amopunt of colour compensating filter.

No, Stefan is right. A 2x converter will double the magnification from 1:2 to 1:1, for example. The focus distance remains the same, hence the extra magnification. You also lose two stops, so a 50mm f2 lens would become a 100mm f4.

Don't forget it's the format that gives different fields of view, not the lens. A 300mm lens is always a 300mm lens.

Not really told off, but sometimes we can over-think things. You seemed to indicate you wanted the best you could for a reasonable price.

No idea whether the U2311 is equivalent or not, it's back to research to answer that one!

Rather than get bogged down in specs and technical details, how about the idea that a Dell 2209WA does the job very well for a fairly modest £250 or so?

Perhaps purchase on Amazon (if available I haven't checked) so that you have a 30 day return policy and you've nothing to lose.

The circle of confusion is a parameter that can be decided upon. Make your requirement for this smaller and you need a higher resolution lens.

In general, smaller formats have a smaller circle of confusion to make a standard print, say 12" x 16", of the the same quality. This means that lenses for smaller formats need to have higher resolution, and they do.

So 645 and 67 lenses do present lower figures regarding MTF as they are targeted at their respective formats. An APS-C lens will need more resolution.

Also, Depth of Focus becomes more critical as formats become smaller, because it reduces, whereas depth of field increases. Depth of Focus is the amount of leeway at the film/sensor plane and smaller formats need more precise location of the film or sensor. There is no free lunch when balancing design in cameras and lenses.

This is why the 110 (and 126) format failed as a precision format - there is no pressure plate in the platic film cartidge and therefore the film plane location was imprecise.

For those who are busy polishing mirrors and cutting down focusing screens, it's a point that should be borne in mind.