Excerpt: Looking for an image stabalized 70-200, I also wanted a lens that was lighter than my 70-200 2.8 and easier to hand-hold. Ths lens filled both of my requirements. The size makes it perfect to keep in my camera bag and ready for use. It also makes it easy to hand-hold.
Pros: Canon L Quality, Consistent Output, Durable, Fast / accurate auto-focus, Lightweight, Nice Bokeh, Rugged, Strong Construction
Excerpt: Great build. Light for its size. Fantastic image quality. As F4, not the greatest in low light, but that's to be expected. Image stabilization is loud, but it works. Expect shorter battery life due to the image stabilization.
Pros: Fast / accurate auto-focus, Lightweight, Nice Bokeh
Summary: I researched the Canon 70-200 f/2.8 L and Canon 70-200 f/4 L IS and came to the following conclusion: WEIGHT: Hands down, the f/4 was much lighter and smaller in diameter than the f/2.8. It is about the same weight as my previous main zoom, the 70-300 f/4-5.6 IS USM.
Excerpt: This is the 2nd time I've owned this lens, and I'm as happy as I was last time. This lens is sharp throughout its aperture range, and its IS works very well. With modern, low-noise-at-high-ISO bodies like the 6D, the F2.8 version is merely heavier and physically larger, not better.