Duh, of course.

What, do you want me to post a couple of pics taken through it, to prove that I know what a polarising filter does?

Look, I know that many of you guys know far more than I do about this stuff. But trust me, I haven't been using a polarising filter on and off for the last twenty-odd years, in the belief that it has a fun rotaty thing on the end just for the hell of it, and also just happens to annoyingly make the viewfinder go a bit dark.

However, I've never had an AF-capable camera before the K10D, so I've tended not to pay too much attention to new-fangled gadgetry until now.

The point is, I've screwed it on to the front; it does its usual polarising thing.

Also, the AF works (trust me on this one too - I can tell, because I half-press the button, it makes a whizzy whirry noise, the picture in the viewfinder becomes sharp, and I get this cool red square in the middle).

So, out of the following possibilities:

- is it definitely a circular polariser (even though I thought it was a linear one)?
- is there something wrong with my belief that linear polarisers bugger up the AF
- or something else?

TIA

Not really a problem...

I've been under the impression that linear polarising filters fool AF into not working.

I have a polarising filter that I've always believed is a linear one; it says, on the side: "Hoya 72mm PL Japan".

I've had it for many years, and it's done its job very well on my ME Super, with my MF Sigma 28-200.

So just out of curiosity, I put it on a newly acquired AF lens (Pentax SMC FA28-200), on my K10D, and am surprised to discover that the AF seems to work, at least with a few indoors test shots.

I've obviously got at least one misconception here - could someone put me straight?

As a postscript to this, following the wise words from the contributors to this thread, I've acquired an example of the Pentax SMC FA F3.8-5.6 28-200 (IF). So far I'm very pleased with it, but have noticed one interesting thing.

If I zoom it all the way to 200mm, and focus on an object some distance away, the object remains in focus if I gradually zoom it out towards the short end.

This was expected behaviour, and corresponds to all the other zoom lenses I've had over the years, although the precision with which focus is maintained on zooming can be a bit variable.

However, this was not true if I focused on something very close first. What happened was that if I zoomed to 200mm, and focused at the closest focusing distance of about 18 inches, and then zoomed out, the subject went dramatically out of focus until it got to about 50mm, at which point it came back into focus again.

Focused on something a bit further away, the effect was less pronounced, until at about 6 feet away and further, it was not noticeable.

It's not at all difficult to refocus when it blurs on zooming, but it does seems strange.

Could someone that has one of these (Mannesty?) please see if theirs behaves similarly?

Thanks very much.

Could you elaborate a bit on why you don't like it, Will? Presumably it's not just the length..

Quite so. I have a Sigma MF 28-200 (PKA) that I've had for many years and it's been extremely useful on walkabouts as you say, including a trip along Striding Edge in the Lake District.

Quite fancy an AF one, hopefully with (even) better optics.

Thanks - I've sent you a reply.

I'm considering an AF 28-200, and wondering about the respective merits of Tamron and Pentax.

The ones I'm considering are:

Pentax FA 28-200mm f3.8-5.6 AL (IF)

and

Tamron AF 28-200 f3.8-5.6 LD Aspherical (IF) (PKA fit).

I'd appreciate any comments on either - and also could someone let me know if IF means that the front element doesn't move when you focus (and zoom, preferably, obviously).

Strongly agree.

I'd also like a closer look at the ones that make up the montage.

Really? I wouldn't have noticed...

I'm not going to have a big moan at you, Pete, this time - I think you are improving, and might put a lot of us to shame in time.

But FFS will you stop describing your pictures as NICE.

Please!!!!

From the "about us" page:

What's all this "not taxed" ???

That's nothing !!!!

My Dad (long time Pentax man - Super A, now K10D like me) - has just bought my Mum....

an Ixus !!!!

Trust you'll flame him good and proper, next time he posts, just to make him feel welcome...