Heard about this legendary lens and was browsing through this review site. Was thinking" How can this be true? How can a zoom lens be this optically perfect?"
I am a 5D user and my 24-105mmL F4 IS was mounted on my camera all the time. At the point of purchase, the 24-105mm L was all the lens I have wanted. My copy was perfect, sharp from F4 onwards. I do not fancy bringing alot of equipment out and changing lens. I was very happy with it for it is giving me very good image quality for 95% of the range I always shoot.
While I was browsing the net for technical stuffs, reviews of 70-200mm F4 kept popping up and it slowly grabbed my attention. There are too many fantastic reviews on this lens and there must be really something abt it.
Although it is not a range I often use, I finally took the plunge, just to see it for myself. And I must say that this lens is as good as the reviews said them to be!!!
The sharpness, colour and contrast is simply fantastic! My copy is sharp from F4 onwards, and there is no discernable difference closing down. I have no hesitation using F4 all the time, except when situations where more DOF is required. The image quality, (sadly to me), brings my 24-105mm L to shame. The difference can be viewed through the LCD, and to me, that is obvious. It makes me suspect if my 24-105 is a bad copy! I still like the 24-105mm for the range it covers, but clearly there are of a different league.
After acquiring this lens, I notice that I am mounting it more, and are taking pictures out of my usual range.
With regards to the built, I think Canon has done a great job. It is the perfect enbodiment of built and weight. The lens is very light in my opinion and yet is of excellent built. Any better built, it will have to be heavier. The zoom is buttery smooth and AF is very quick.
About the IS.... I think I can't live without it. It has allowed me to take photos of situations technically impossible before. The IS in this lens is also better than that of the 24-105mm. For the style of photography I do, IS is a dream. It allows me to keep shooting while others have to pack their gear. I would strongly encourage anyone to consider the IS version. Although it is much pricier, it is still worth the difference. Ask yourself, how many times is your shutter speed below 1/30th of a second and you can't have a reasonably sharp shot? With IS, you CAN!!! How I wish all lens come with IS.
I also notice I have been shooting at 200mm F4 alot of the times, because I prefer the perspective and bokeh. I do wish for the DOF to be shallower, but this is inherent in an F4 lens. Planning to get the EF 100mm F2 next. (not no IS!)
Summary: This lens is as good as they said! If the range is useful for you and F4 aperture does not pose a problem, do not hesitate. Don't forget to get the IS version.