Do you use the lens on any bodies that can't control the aperture setting themselves? If not i'd be inclined just to turn it to "A" and leave it there.

Pentax *istDS, Vivitar 55mm F2.8 macro

As gartmore says the main problem with this is the price of the adaptor - I considered getting one for 645->K, or 67->645 but they're too expensive to make it worthwhile.

I did buy an adaptor that allows me to use Pentacon fit lenses on the 645 though, so I've now got a couple of Carl Zeiss lenses for it.

Shooting birds in flight is pretty tricky, I remember trying it once with a 500mm F8 mirror lens - my hit rate was just about as bad as you'd expect.

Fast AFC helps a lot although it's still best to take a lot of shots to ensure some have the main focus in the right place.

That shot looks pretty decent - I'd be tempted to crop the sky to the right of the bird so it's flying into the frame rather than central. It looks like there is a fair amount of colour fringing around the tops of the feathers and the focus point looks like it's on the near wing rather than the centre of the bird - that's the main problem I usually get as well and when shooting wide open it usually means the birds eye isn't sharp.

I'll have to drag myself out to one of the islands in the Forth again and have another go with the seagulls.

The prime lenses will be considerably sharper than consumer spec zooms like the ones mentioned - especially at larger apertures, and also away from the centre of the image.

Those primes are also significantly faster than the zooms and that offers more flexibility when shooting in low light, stopping action and for limiting depth of field.

I've had a quick look and it doesn't explain how it'd cope with anything other than whatever the standard focal length of their "digital lens" is - as such as you stick either a wide angle or telephoto lens in front of it then unless you always shoot at minimum aperture (with the associated problems that brings) then any effect is going to be limited.

I can see the benefit for point and shoots (using digital zoom) but I'm not convinced it's all that applicable to SLR type cameras.

That's what I do as well, primarily on pbase as you can select a lens and the site gives you random examples from all the shots posted with that lens. You have to trawl through a fair amount of crap of course but it's a good way to see the sort of results people are getting with a particular lens.

Very true. I bought a lot of old lenses in the last year or so (mainly M42 but some K-mount as well) and it's quite interesting to see what affects the value. Sometimes it's just the manufacturers name (e.g. a Sigma 24mm F2.8 is worth noticeably less than exactly the same lens with a Carl Zeiss badge on the front) but in others it's optical e.g. the SMC-M 28mm F3.5 usually sells for more than the SMC-M 28mm F2.8 because it's sharper (although the F3.5 is probably rarer).

At the moment I'm building a Pentax 645 system and the value of some of those lenses (especially the wide angles) has held up very well over the years. One of the lenses I've got coming from it is a pretty old Carl Zeiss Flektogon 50mm F4 (in Pentacon 6 fit as I've got an adaptor) that's probably worth significantly more now than it cost when new.

Not very much unless it's a very, very small company!

I suspect most pro's will write their kit down over something like a 3-year period - even if the general re-sale is still reasonable for such kit 3-years of professional use will erode that considerably.

I'm also in business, although IT rather than photography, and we account for computer equipment purchases on the basis that they're more or less worth nothing after a 3 or 5 year period.

I think that given the volatility and rate of progress in the digital camera market it'd be unwise to assume that any of the current APS-C sensor size lenses will necessarily be all that valuable in say 10 years time.

If larger sensors drop in price then that could make the APS-C lenses redundant, and going the other way if sensor technology improves to make smaller sensors viable for serious photography then the ultra-wides would then become more like standard zooms (or merely wide).

I buy DSLR bodies and APS-C lenses on the basis of the use I'll get out of them in the next 3 or 4 years, but with the assumption that they'll be worth little after that period (almost certainly that'll be true for the bodies, maybe not for the lenses).