Chris: You get what you pay for.... Having owned the 70-200 mk I, I had always wondered if the 100-400 would be better as opposed to adding the 2x to the 70-200... I'd planned to buy this one and I'm glad I didn't!!!! We took this lens on a week long road trip photographing everything from landscapes to wildlife in all lighting conditions. The copy I used seemed to work okay from 100-around 250/300mm.... from 300-400mm the results are pretty disapointing using a full frame sensor (5d mkiii). Even on tripod, zero difference. Hand held using both IS settings and a lot of patience.... still pretty lackluster. There's a clear difference in my opinion with sharpness, contrast, IS, focusing speed using some of the new lenses vs. this older design that's simply ready to be retired. On a positive note: My experience with Borrowlenses has been amazing. They've gone above and beyond to get me items on time and answer my questions!!

Chris: I rented this lens last November to use on a photojournalism assignment to cover a Presidential visit. This lens did not perform as well as I had hoped. It isn't sharp at all, and it's hard to get it to shoot under f/5.6. It was cloudy on the particular day I used it, and I had to crank my old Canon XT up to ISO 800--and as a result most of my images were unusable due to grain. The lens is very cumbersome to use. It's huge and heavy, and zooming is quite difficult. Instead of a standard twist-to-zoom set up, this lens is zoomed by pulling out/pushing in the front part of the barrel. This made it very tough to zoom in and out quickly while still balancing the lens. All in all, this lens was a disappointment--I really don't think it should be an L series lens. I've gotten much better shots with my cheap 75-300 f/5.6 III. However, I might consider giving it a second try if I knew I would be using it on a sunnier day.

alibaba: This is a big, heavy lens with an old school pull-push zoom mechanism. I rented this for a day at the beach taking pictures of surfers, and found that it's not the sharpest lens but with any lens with this range of zoom you don't expect the best quality. If you rent this lens, you should definitely stay away from 400mm range as you loose quality noticeably, 300mm would be your best bet. Using the pull-push zoom was interesting and easy. the friction ring is very helpful. the IS works great. This is a heavy lens so make sure you at least rent a monopod or tell your arms goodbye as they'll be toasted if you use it handheld.

Eliya: In spite of IS, this lens does not perform well without a tripod or monopod. I was hoping this would be a perfect hand-held lens for photographing wildlife on nature hikes, but I've been consistently disappointed with the quality of my photos. At f/5.6, you need a pretty high ISO to get the shutter speed down to something you can shoot hand-held, and even then, this isn't the sharpest of Canon's L lenses. Consider the faster and lighter 300 f/4 as an alternative. A 1.4x extender will make the 300 into a 420 f/5.6, and this combination will still autofocus (albeit slowly) on a crop sensor camera like the 7D. The 100-400 loses autofocus capability with an extender. If you're shooting on a tripod or monopod, this lens should be fine, and the zoom ability can be useful, but one of the heavier prime lenses might be a better bet.

Larry: I've used this lens on various assignments and it is great in good light if your needs dictate it. I shot the America's Cup World Series Regatta / Fleet Week in SF recently and it is quite handy all purpose lens. Mind you, I would rather shoot my prime 400mm f2.8L for most sporting events, but this lens is good. For shooting the AC45's on the Bay to the Blue Angels, it was much easier to maneuver through the crowds and carry than the "big glass". I think it's a good overall sports type lens.

Larry: I've used this lens on various assignments and it is great in good light if your needs dictate it. I shot the America's Cup World Series Regatta / Fleet Week in SF recently and it is quite handy all purpose lens. Mind you, I would rather shoot my prime 400mm f2.8L for most sporting events, but this lens is good. For shooting the AC45's on the Bay to the Blue Angels, it was much easier to maneuver through the crowds and carry than the "big glass". I think it's a good overall sports type lens.

Jason: Excellent lens, great build. It may have just been my choice of backgrounds as I was shooting, but I found the bokeh on this was not as smooth as some of the other Canon glass I've used. Shot the NCAA Div I Football Finals game with this in January (handheld!), as well as using it on a road trip. Great clarity, fast enough for full daylight levels, but found it a touch too slow for a night football game, even with the large amount of lighting. The push-pull zoom takes a little getting used to, but once you figure it out, it is very convenient. I loved the ability to lock it at a certain focal length. I would not recommending going handheld for long periods of time unless you can't take a mono/tripod with you (many stadiums don't allow them).

Charles: Amazing lens for soccer photography. The lens might seem a bit 'slow' at f4.5-5.6, but at least under the lighting conditions I was shooting under (evening, sunny summer day), it was more than fast enough The push-pull zoom takes a bit of getting used to I also found the lens very contrasty, which is a good thing.

Tom: I recently rented the Canon EF 100-400mm f/4.5-5.6L IS USM to shoot pictures of my son's baseball team at a big tourney. I have nothing but great things to say about BorrowLenses.com and the lens. The lens arrived on-time (I only ordered it a few days before we left) and the price (including shipping and insurance) was the lowest I found and I shopped a number of the lens borrowing sites. The lens itself was great. I had read a bit about softness of the image when shooting on full telephoto, even asked about it at BorrowLenses.com (via real-time chat helper) and was assured the lens I'd be renting was not older than 2 years (seems the older versions of this lens had the soft issue) and I have to say, my photos were crisp and clear even at full-telephoto. Some folks say that push-pull zoom was hard to get comfortable with but I have to disagree. I found it quite easy to use -- I even had my 10 yr old taking shots and he too found it quite simple to use. Would highly recommend this lens to anyone that needs the ability to shoot close ups at a distance (sporting events especially) but also wants a bit of flexibility to shoot at a more normal zoom for things like team photos, etc.

Megamoneybags: I absolutely LOVE this lens! I brought it with me on a 6-day vacation to Tennessee and it was basically the only lens I used! I assumed the push-pull system would be unusual to handle, but, it is just like any other telephoto lens, except, you can lock the lens at a certain focal length. It is a little heavy though, but not heavy enough to where you need to use a monopod (trust me, I spent a whole day hiking while holding this lens, it's not that heavy!) Many reviews have stated that the lens is "soft" at 400mm, I strongly disagree with that. My results at 400mm where just as sharp at 100mm. I even printed a few photos that were taken at the 400mm focal length, there are no signs of "softness"! I plan to purchase this lens soon!