The point I would make David is that we don't actually know. We know of some failures (how many?) but we don't know, as ronniemac points out, those that didn't fail as that isn't something that's newsworthy. It's anecdotal as it stands and I wouldn't let it stop me buying an SDM lens. In fact, we have some and they haven't been any different to the DC lenses or the screw drive ones for reliability. But that too doesn't mean anything.

I have some statistics somewhere on the failure rate of VHS video recorders, from about 1980 or so, and in the first year some 35% of them failed for some manufacturers. Now if that happened with SDM lenses we would have a crisis. But we simply don't have the data to judge, and that's the only point I make.

In terms of quality of results it all works very well, but I do think it's very clunky and inconvenient in design. The GR on its own is a very nice bit of kit, but add the rest and it's cumbersome.

Thanks for the Ad but please just post here in Classified rather than repeating the info all over the forum. Many thanks.

Many thanks for the correction!

Lenses project a curved image onto a flat surface, and good ones do it very well, managing to keep centre and edges in sharp focus at the same time. This is especially true of macro lenses, which are often used to make flat copies.

A cheap lens will show field curvature and at wider apertures the edges may not be in focus when the centre is. This is easy enough to discover using a newspaper as a target. One solution is to curve the film/sensor so that everything is in focus.

The other thing is deliberate field curvature and Minolta made a VC lens where the amount of curvature could be dialled in. This made semi-circular groups of people easy to photograph without distortion and whilst keeping them all sharp. It's not been a mainstream idea that's caught on in any great way, except probably within the secrets inside inexpensive compact cameras.

The point I'm making Rob is that Swarf's lens could be the only one that's failed in the last three years, we have no idea what the percentage failure rate is.

There has been no history of problems with the 200mm f/2.8 lens.

This stems from some early problems with a design fault in a couple of SDM lenses and it was tackled years ago by Pentax. There will always be some failures of any item, but SDM should be as fine as any other focusing system motor. WE haven't heard much about the issue for a very long time.

It's been done before with cameras with curved pressure plates for film. The idea was that it compensated for cheap lenses that were mass produced. I'm sure in a modern context that won't be the reason though!

Don't forget Pentax User Plus members get 20% discount on servicing from JPS. Well worth the modest cost.

It may well be the browser settings rather than the site settings. I've removed the screen grabs as they provided all the links to a spammers websites. Always try to avoid spreading the spam please, for the same reason that we don't quote spam posts.