Most of the reviews of this beast (or beauty – depends on how you see this), on the net, are written by professionals, for professional. I am no professional, so if you intend to buy this lens, or even are thinking about something on this range – Read on.
Don’t get threatened by the long name of the lens – Now I’m assuming you’re shoot with a Canon system, because there is this lens is meant for canon users.
EF conveys that that the lens is compatible on a Full frame sensor or a 35 mm film camera. Effectively, on an APS-C sensor, you get the equivalent range of 160-640 mm without any degradation in quality or loss of f-stop. f/4.5 – 5.6 indicates the aperture varies from f/4.5 at 100mm to f/5.6 at 400mm. USM is the fast focusing motor from Canon, L denotes the luxury grade lens known for its ruggedness and quality of optics, and IS denotes that this lens comes with a built in stabilizer.
What’s in the box when you buy this lens :
1. Canon EF 100-400 lens
2. Lens Pouch – Not well padded, maybe good if you are storing the lens, carrying it around in a backpack.
3. Tripod Mount Collar – Thankfully, Canon decided to give this in the box.
4. Lens Hood – Plastic hood.
One of the first things that you will notice is the weight. At 1.3 KGs, its neither too heavy to handhold, nor exactly light for those migrating from the 300 mm range. Then you start fiddling with the lens, and you realize that the the push-pull design is confusing – it took me a while before I could figure out how to unlock the zoom mechanism. There are four buttons on the left of the lens – Auto/Manual focus toggle, Range limiter, IS On-off, IS Mode (Mode 1 stabilizes horizontal and vertical, Mode 2 stabilizes only vertical – useful when panning). Mount it on the camera, and jeez, that’s actually heavy. Viewfinder, half press of the shutter release button – surprise surprise! Focusing is fast (even on a entry level dSLR body), and for those migrating from non-IS lenses, you have to be blind to miss it, or maybe you didn’t turn the IS button on! 
Now for the details – There is a lot of talk on sharpness, Image Stabilization and Image Quality. Apparently, there was a problem with sharpness in a few lenses that were manufactured earlier – If your copy is a recent one, you’ll most likely not notice this behavior. Older lenses were sharper at f/8 than f/5.6 – There are plenty of websites that tell you how to test sharpness. I’ve not noticed a difference in sharpness in the images at f/8 and at f/5.6. My copy of the lens has given me acceptable levels of sharpness.
Sharp enough?
Or How about this?
With respect to image quality, I don’t find issues with the lens. Color reproduction is excellent, and I don’t have to spend a lot of time processing the images for color. It also gives me a wonderful bokeh.
The Image Stabilizer on this lens is supposed to be a 1.5 generation stabilizer. I don’t use a tripod, so can’t say much about it’s use or behaviour when mounted on a tripod. There have been reports of erratic behaviour as the lens tries to stabilize movement when mounted on a tripod. From what I’ve used, the the stabilizer works very well when used handheld. I’ve been able to get shots at 1/25th of a second when shooting handheld.
The photo is a little cluttered, but the sharpness at 1/25th of a second speaks for itself
I primarily use this lens for bird / animal photographs. It is tough to get an image of a bird with a 400 mm lens that may not require cropping, but on following proper approach or if the bird is cooperative, you’ll be able to fill up the frame with an image of the bird.
The other huge concern is the push-pull design and mis-informed users. I’ve heard folks telling me that UV filter is a must as the lens has a push-pull mechanism – Something that I can not understand why. While it is unconventional, I’ve not noticed any increase in dust on the sensor than what it was before I picked up this lens. While I do agree that it does take a little bit of learning to understand the use correctly, and that if careless, the lens can snap if you have not tightened the zoom lock and point the lens down, or otherwise. So take care that the first thing that you do after you fix the lens at a specific focal length is to tighten the zoom lock.
It took me a while to get adjusted to the camera + lens weight combination. I’ve so far never used a tripod with this lens. I should say this lens has been my primary workhorse, and has helped me build up my arms.
Other alternatives if you’re considering this lens:
1. Canon EF 400 f/5.6 L USM – Lightweight, and a few have mentioned that this lens can focus faster than the 100-400. There is no IS though. Good lens for birding.
2. Canon EF 300 f/4 L USM IS – Another small lightweight lens. You can add a 1.4x TC and get 420 mm equivalent at f/5.6
Please note that though there are third party alternatives, I’m not suggesting any as I’m not sure how compatible they are with a full frame camera or with new cameras.
Things that I would like Canon to improve on for this :
1. Better hood – Metal hood would be much appreciated.
2. The zoom lock merges with the focusing ring – This creates a lot of problems when trying to operate the zoom lock with one hand. I’m surprised that very few people have mentioned this.
In conclusion, does the price tag of this beast justify it’s performance? I’d say yes, this is one of the best lenses in the range. If you’re still thinking about making a decision, here are some images that could help you.
PS : I’m thinking of converting this into a website to share information on photography – Tips, tricks that I know of, along with some equipment reviews.
PPS : I’d originally written this for Chitra’s blog
Good review. Thanks. I do want to comment on one thing that was said that I’ve seen extensively elsewhere. The 1.6x multiplier of the APS-C sensor actually refers to the field of view . This 100-400 lens on an APS-c sensor does NOT give you the equivalent range of 160-640mm. What you get is what is still a 100-400mm range, but with the Smaller Field Of View of a 160-640. This can be seen by taking a shot of anything with this lens on a full frame camera (digital or film) and then mounting it on an APS-C camera shooting the same subject from the same spot. There will be no extra magnification or reach. In the photos, the subject in the center will be the same size and all else being equal have the same depth of field, sharpness, etc. What will be different is that the full frame shot will encompass a much larger area, there will be more of what’s on the side, top, bottom, etc. This should not be judged a problem with this lens. It is true of all lenses when matched with the APS-C (or equivalent for other brands).
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