If you get a 18/250 there is no need for the change you have all the bases coverd which is the whole idea. I tend to stick my sigma 17/70 on one camera and the Tamron 70/300 on the other that way I cover quite a focal range. I also have the sigma 10/20 so I can vary things. For four hundred pounds you will have over a hundred pound change.
Ian

Im not they make some cracking good lenese you also need to consider price as well.
Ian

[IMG]http://i23.photobucket.com/albums/b399/philstaff/IMGP4012-1.jpg[/IMG]

[IMG]http://i23.photobucket.com/albums/b399/philstaff/swan5.jpg[/IMG]

[IMG]http://i23.photobucket.com/albums/b399/philstaff/swan4.jpg[/IMG]

The above was taken with the Tam 70/300 I think if you do a search you can pick it up for around £90 or even less. Only problem is you will not have the scope at the wide end of the lens compared to an 18 250.

http://www.photozone.de/canon-eos/293-tamron-af-18-250mm-f35-63-di-ii-ld-aspheri...

http://www.photozone.de/pentax/367-pentax-smc-da-18-250mm-f35-63

Here are two reveiws on both I have the Tam 70/300 and love it.
Ian

http://www.pbase.com/pfang/fang&page=14

Came across this guys album on the web and just love his work and wonderd what others thought.
Ian

Probably my sigma 17/70 but as said earlier I would miss the rest quite badly.
Ian

Hi Peter there a quite a few blues about recently however its not a col I would choose myself it often comes with a light col amber eye and a lack of pigmentation in some cases.
Ian

Yes Peter he is a 14 month old Staffordshire Bull Terrier.
Ian

Were you expecting something else LOL.
Ian

[IMG]http://i23.photobucket.com/albums/b399/philstaff/hd2-3.jpg[/IMG]

[IMG]http://i23.photobucket.com/albums/b399/philstaff/hd-1.jpg[/IMG]

Works just fine on the K10 and K100 D once you sort the programe out.
Ian