new lens?

carnt make my mind up on a new lens 24-105 or 70-200 f4 is. for a allround lens i have 40d and 17-85 and 100-400 what do you think?

What I'm thinking is it's not worth buying a new lens to fill in the 85-100mm gap you currently have. Are you wanting to upgrade from the 17-85? If so, that's a different question.

yes i am thinking of a new lens to up grade fom the 17-85

What about a 17-55 f/2.8?

I would go with the 24-105 F4 It is going to be my next lens. I used it on vacation for a few hours and it is a great walk around lens. As Rick Sammon says if he could have only 1 lens it would be the 24-105

But the 24-105 makes a much better all-round lens for full-frame than for APS-C cameras. Many people like the 17-55/2.8. The new 15-85 is the crop equivalent to the 24-105L and is said to be considerably better than the 17-85. My feeling is that 24mm is not wide enough for an all-rounder on a crop camera, but you could always go for something like the 10-22 later to cover that end of the range.

Madweasel wrote in post #8978485
My feeling is that 24mm is not wide enough for an all-rounder on a crop camera...

No, it's not. When I was using a 20D I also had a Tokina 17mm f/3.5.

Well are you keeping the 17-85? if so get the 70-200(whats lacking about the 100-400 can the f4is fill what the 100-400 is lacking?). If your giving up the 17-85 get the 24-105

thanks everyone i think i will go for the 70-200. as I am keeping the 17-85 and see how i get on ?

I think you will really enjoy the 70-200, its one of the sharpest lenses I have seen. good choice