[quote="TheVicar"] the Sigma 120-400 HSM weighs 1.64kg[/quote]Good grief !!!
The Tamron is 'only' 800g but that's twice that of the 55-300. It's also quite long and I'm conscious of having to take care to support it all the time.

The focus is fine when I use the 18-55 kit lens, AF or MF. The blurred shots when I first got it were definitely down to bad technique and camera shake when not using a tripod! I've been working on that.
The problem arises when I use the older Tamron zoom. The photos are fuzzy (not 'fussy' as I put earlier) so whether that is me or the lens itself, I don't know. I do find it incredibly difficult to focus and it didn't make any difference whether I trusted my eye or used the beep. You wouldn't believe how disappointed I was with some of this afternoon's shots (but I expect you've all been there !)

I also have an older Pentax 50mm lens and have got a couple of nice sharp images with it, so I don't think there's any problem with the Kx.
I don't think either lens can be used on AF - they are from my non DSLR Pentax days.
It's possibly the Tamron lens itself which I've noticed on longer shots does produce 'soft' pictures, which isn't really what I want.

It looks as if the Pentax is the one to go for since nearly all of you sing its praises and is about what I had hoped to pay. It sounds ideal in all ways - and should be a good lens to learn with.

Does anyone want to buy an old Tamron SP 70-210 ?????

Just crossed : Paris is easy to get to from where we are.
YOu don't happen to want to sell your 55-300, Carl ?

Many thanks for all your help, everyone. I'll think carefully about the above - it is likely to be choice between the 3 you mention above, Carl, all of which find favour here.
I do think I would find using a modern zoom a lot easier than the old one - it feels too much like hit and miss at the moment.

Anyone interested in a Tamron SP 70-210 ???

Amazing shots - No. 7 does it for me - a great feeling of speed.

Many thanks for the all the information - greatly appreciated. I do understand that in the end a lens is a bit of a personal thing ... and of course can be dependent on budget !

I'm sorry to ask what probably seem elementary questions, but :
Would a non-Pentax lens - like the Tamron 18-250 - fit straight onto the Kx?
Would it need an adaptor?
Would all the camera's functions work as they would with a Pentax lens?

Well, I have to admit, that after an afternoon of fussy failures with the old Tamron, both with and without the tripod, I will have to get something lighter and easier to manage. It's utterly depressing to find that what should have been good shots were blurred.

I went back out and use the 18-55 and did a little better.
Of course it is most likely down to operator failure - but I just don't seem to be able to focus.
Even with the beep on, the shots were unmentionable.

Yours, a very disheartened Blaze ..... but then tomorrow's another day

They look pretty good to me - thanks Ian.
You've obviously got steady hands ....... or a tripod ???

Apologies if I'm being vague. There are so many different combinations available - some that do specific things and others that seem to do everything - that I'm not quite sure what I should be looking at.

I have the DAL 18-55 which came with the Kx and I've just seen the DA 55-300 lens online and the price looks about right. I'm not sure I'm ready for a super zoom, so this may well be what I should be looking at.

I've just joined a local photography club so I rather hope I'll be able to get some practical experience (provided they're not all Nikon/Canon fans). Sometimes on the spot practical help and advice can be very beneficial!

Thanks, Jeeess. That's just the sort of comment I needed to hear (I'm not joking !). I guess you get what you pay for.
The Pentax lenses are fearfully expensive which is why I'm looking at other options.