And one more question: do you tend to leave the adaptor rings on once fitted? Or to put it another way, should I buy one 52mm and share it between two lenses, or splash out for two?

Thanks once again to everyone for their help, especially Matt for putting me on to Speedgraphic - as you say the ND grad kit for P looks an excellent way in. Would you expect P to work ok on the 14mm f2.8 DA, 77mm thread? That's the biggest I can imagine needing.

Thanks, guys. Anyone used any filters from Kood, currently advertising Cokin compatibles in the magazines at reasonable prices?

Thinking about investing in some grad ND and circular polarisers. At the moment have the two K10D kit lenses (18-55 and 50-200), which both happen to be 52mm filter thread, and my brand new 100mm macro, which is an old-fashioned 49mm. I guess at the moment the smaller Cokin size would do fine, but am I going to regret this if I buy more lenses later? Anyone dealt with this sort of issue, or made mistakes I can learn from?

Thanks for the virtually instant, and very helpful, reply John.

I've managed to acquire a nearly new lens at a cracking price - low enough to steer me away from the Tamron or Sigma alternatives. Can anyone give guidance (or point at some) on how and when to use the focus locking device?
Many thanks.

Daniel
Are you sure SRS have the 105 in Pentax? After a conversation with Chris a couple of weeks ago I understand there's quite a wait for both this and the Tamron 90 in the UK.

Thanks Dan. Took a look at the Ffordes site. It's not terribly clear whether the lens is the current Di spec - if it's not, it's definitely overpriced. And I'm in Guildford, which is fair way from Inverness. Interesting, though, I might call them.

Hmm, offbeat is right. As a macro novice, the advice I've been given is that even a 50mm macro puts you uncomfortably close to the subject. So I'm either going to get the Tamron 90 or the Sigma 105. As the Pentax 100 is more than £100 more expensive, with minimal if any quality advantage, I've reluctantly decided against it.
Although I'm now willing to make the purchase, it's a bit academic at present, as there's such a surge in demand for Pentax fit lenses that there's a wait of several weeks for delivery of either of the above.

Those are great, Mr Spider. I shall be very pleased if I end up producing anything like that sort of quality.