If this is the Sigma A-Series 400mm F5.6 (non APO), there are black ones, grey ones, MF ones and AF ones.

There's no difference AFAIK between the black and grey, and the AF ones tend to go for about 60 quid more than the MF ones. Good AF ones were going for about £160+ a few months back when I last looked.

I've owned three - 1 AF grey and 1 MF grey, which I've now sold, and an AF black one, which I've still got.

They're not bad. Quite a lot of CA wide open, but very light and usable, especially the AF one which focuses very quickly on the K10D, and sharp enough stopped down a bit.

These were all with the AF one:

http://i162.photobucket.com/albums/t244/chris5gd/Aviation/IMGP5505-smsh.jpg
http://i162.photobucket.com/albums/t244/chris5gd/Aviation/IMGP5502.PEF1smsh.jpg
http://i162.photobucket.com/albums/t244/chris5gd/Aviation/IMGP5482-1smsh.jpg
http://i162.photobucket.com/albums/t244/chris5gd/Aviation/IMGP5481-1smsg.jpg

The thing is, all these lenses are well over 20 years old, and all that seems to be wrong with a few of them is part of the mechanism - nothing to do with the optics, which seems universally praised.

My impression (and that's all it is, but a strong one, even so) is that the current crop of 16-50s has given rise to far more QC-related worries than any of the preceding generations of Pentax lenses.

I realise that the internet makes it a lot easier for this sort of thing to get about, and I'm a relatively new kid on the block when it comes to an active interest in gear.

Was it ever thus?

Great news.

I rest my case.

Can't argue with any of this, John - and I haven't had any problems myself, and nor have my dad or brother, who also use Pentax equipment.

But there seem to be almost no comments here about problems with older lenses, nor about misfocusing with older cameras.

I don't really know, and of course anecdotal evidence is unreliable statistically, for the reasons you say. But some of the 'Pentax made my camera worse' stories are worrying.

Only comments here and at PentaxForums.com - people seem to be having a lot of trouble with dud copies of lenses, especially the 16-50, and also with getting Pentax to fix things.

I haven't done a systematic survey, but my impression is that QC and service are not what they should be.

It is. But anecdotal evidence here and elsewhere is accumulating fast, to the effect that Pentax is not aware of this.

Thanks

Well mine's new (from SRS Microsystems in Watford), so I can't comment on how it goes over time - I only bought it a few days before I went away last week.

However, it's been used continuously for a week on the K10D (600 shots, most rubbish ), and it still feels just as it did when new. The zoom is very smooth, precise, very pleasant to handle.

The AF is quick, and no noisier than other Pentax fit AF lenses I've used. However, as others have noted, sometimes the camera seems to think it's in focus over an enormous distance range (especially at the wide end), and not change its focus point if you focus, say on 3 feet, and then try and refocus on something at infinity.

Other times though (most of the time in fact), it does exactly what you'd expect, and refocuses fine.

It shows virtually no purple fringing (even with harshly overexposed sky behind branches and twigs - conditions which almost guarantee PF with many lenses).

It also shows very little chromatic aberration.

In the shots I posted, I've removed a little vignetting that was noticeable, but possibly that was caused by the UV filter (pace, George).

As far as sharpness goes, I haven't yet done any proper testing, but the bigger versions of the pics I posted seem fine, and apart from a couple where I inadvertently misfocused, there don't seem to be any problems. All my shots were at F8-11, IIRC, so I can't say much about other apertures.

Someone else posted a picture with noticeable distortion at the wide end at the edges, where straight lines weren't quite straight, but I can't say I noticed it in the shots I took.

So far, I'm very pleased with it. I've never owned a super wide-angle lens before and apart from the inevitable need to have the camera very horizontal to avoid the tilting verticals, I've not been in the least disappointed.

Agreed. There wasn't a great deal I could do about the colour - it was bright blue skies, mostly with the sun overhead (apart from Tarn Hows which was shot in the very late afternoon), and very little cloud most of the time. What you see is pretty much what it looked like. I've only evened out the shadows a bit, and increased the contrast. I didn't even have a polariser, fool that I was not to think of it in time.

I'm a complete beginner when it comes to landscapes - never really got the hang of them.

I thought of you, though, for the B&W conversions. Not in your league though

We came down via Warnscale Beck (just did what AW said, basically). It was easy enough, and we were very glad we did it that way round. The scrambly bit just before the top looked a lot harder to go down than up. I even had to put the camera away for a bit!!

Thanks again.