As a follow up to this thread http://forums.macrumors.com/showthread.php?t=456367. Firstly I should have listened to you all! While the Canon 55-250mm IS is a great lens. I've been impressed with the pictures, it doesn't quite have the focal range I want and that large F5.6 at 250mm has been restrictive in low light conditions (sometimes forest area's or overcast skies, I live in the Uk after all!!) when shooting motor sports. I'm now considering getting a better/bigger lens and need some advise. I've been looking at the Canon EF 70-300mm f4-5.6 IS USM for around £340. While this has the increased focal length and from what I gather a slightly better build quality of the 55-250IS it still suffers from the aperture problem. Another that I've been looking at is the Canon EF 70-200mm f4L USM for £390, however this doesn't have the focal range. I could always get the 1.4x extender but as I gather it would increase the F/stop one or two? Anyone any pointers? Other lenses to consider?