Until it was replaced by the Canon EF 16-35mm f/2.8 L II USM Lens, the Canon EF 16-35mm f/2.8 L USM Lens was my first choice for a full-frame, wide field of view, low light lens.
Measuring 3.3" x 4.1" (83.5 x 103mm)(DxL) and weighing 1.3lb (600g), the Canon EF 16-35mm f/2.8 L USM Lens is relatively small and light. Build quality is very high - indicative of its Canon L Series heritage. This is a very nice handling and carrying lens. It is easy to take this lens with you - mounted or in a case.
"In a case" has special merit as a short focal length range (inhibited primarily on the long end) is one of the downsides for this lens. The 16-35 L works great by itself, but it is especially useful in a kit with a 24-XXmm and/or 70-XXXmm or similar focal length range lens(es).
Utilizing Ring USM, the 16-35 L focuses very fast, quietly and accurately. The focus and zoom rings are nicely sized, turn smoothly and are nicely damped. This lens does not extend with a very small exception - the objective end lens elements move in/out slightly inside the lens barrel during focusing. All movement takes place behind the filter threads. If you have a filter installed, you will not have any external movement. Since the filter attaches to the lens barrel - which does not move, the filter also does not rotate. This matters when using a Circular Polarizing Filter or split neutral density filter. The common 77mm filter threads make sharing filters with Canon's complementing lenses easy.
The 16-35 L is weather-sealed but I suspect that this lens requires a UV Filter to complete the sealing. The Canon EF 17-40mm f/4.0 L USM Lens shares the 16-35's small lens element extension feature, and the 17-40's manual indicates that a filter completes the sealing. The 16-35 manual does not specify this.
At 16mm, the Canon EF 16-35mm f/2.8 L USM Lens is very sharp in the center even wide open (f/2.8) and improves little when stopped down. The 16mm full-frame corners are soft wide open (with a flat target - because of field curvature) and improve noticeably at f/5.6. At 16mm with a close subject distance, strong barrel distortion is noticeable even on a FOVCF body. Barrel distortion enlarges the center portion of the frame and shrinks the corners. This effect makes the center performance at 16mm seem especially good when in direct comparisons with lenses exhibiting less barrel distortion. You will likely notice this when comparing the 16-35 L's 16mm ISO 12233 resolution chart sample crops with other lenses and focal lengths. Distortion is much less of an issue with longer subject distances - I seldom find it to be a big issue in my real-life images.
While on the ISO 12233 chart sample crop subject, I should note that the 16mm samples require a relatively close subject distance. It is very hard to eliminate light reflection from the chart in the edge sample crops at this distance. You will notice lower contrast in the bottom 16mm ISO 12233 chart sample crops because of this.
By 20mm, the 16-35 L's barrel distortion is dramatically lower and corners sharpness approaches center sharpness. Sharpness wide open is very good across the focal length range with the longer end being slightly weaker than the wide end. By f/4, this lens is very sharp across the frame.
One of the most notable negative features of my 16-35 L is a tendency to overexpose. As long as I do not clip highlights (because of this tendency), color and contrast from this lens are superb. CA (Chromatic Aberration) is very well controlled. A 7-blade circular aperture delivers excellent OOF (Out of Focus) blur quality. Of course, it takes a close subject and a wide aperture to get a significantly OOF background with this ultra-wide angle focal length range. Flare resistance is very good - very important as it is easy to get the sun in a 16mm image.
Users of 1.6x FOVCF bodies will enjoy near-vignetting-free images with the 16-35 L. Full frame users will notice strong vignetting at 16mm f/2.8 and moderate vignetting at f/2.8 over the remaining focal length range. The full-frame vignetting is primarily noticeable in the outer corners of the frame.
Since filter-caused vignetting can become an issue with ultra-wide angle lenses, it is prudent to compare the vignetting with and without a normal UV filter attached before making a filter purchase for this lens. The comparison (link at top of review) in this case shows that a normal-thickness UV Filter does add a little vignetting at 16mm f/2.8 on a full-frame body. Is it enough to justify using a slim UV filter? You will need to answer that yourself, but I typically use a normal UV filter with this lens. However, since a Circular Polarizing Filter is about as thick as a normal UV filter, a normal CP Filter will cause noticeable vignetting at 16mm. Again, 1.6x FOVCF body users will not need to worry about the normal thickness filters causing vignetting.
Pictured above from left to right are the Canon Extender EF 1.4x Converter (for reference), Canon EF 16-35mm f/2.8 L USM Lens, Canon EF 135mm f/2.0 L USM Lens, Canon 24-70mm f/2.8 L USM Lens and Canon EF 70-200mm f/2.8 L IS USM Lens.
At its closest-focusing-distance of .9' (.28m), the Canon EF 16-35mm f/2.8 L USM Lens delivers its maximum magnification of .22x at 35mm (a decent value). A 16mm shot at this distance delivers a dramatic perspective. Adding extension tubes to the equation shortens the closest focusing distance and delivers significant (macro-realm) .86x and 1.09x maximum magnifications for 12mm and 25mm tubes respectively.
The 16-35 L ships with a Canon EW-83E lens hood and a Canon LP1319 soft lens pouch. The shape of the hood (very wide and very short) makes one question whether it actually helps. It does almost nothing for lens protection - and probably nothing for 1.6x body image quality. It also makes storage inefficient. With the hood removed, the 16-35 easily fits in a relatively small Lowepro Lens Case 1W. To accommodate the diameter of the hood installed, the 16-35 requires a relatively large Lowepro Lens Case 4S.
Although the Canon EF 16-35mm f/2.8 L USM Lens performs superbly on a 1.6x FOVCF body, EF-S compatible body users should also consider the Canon EF-S 17-55mm f/2.8 IS USM Lens when looking for a fast, wide zoom. This lens is at least as sharp as the 16-35, has a longer focal length and has image stabilization. It is larger (and extends), is not as well-built and is not weather-sealed (but the EF-S compatible bodies are not sealed either). If a full-frame (or 1.3x) body is in your not-too-distant future, an EF-S lens may not be a good investment for you.
Another lens that competes directly with the Canon EF 16-35mm f/2.8 L USM Lens is the Canon EF 17-40mm f/4.0 L USM Lens. These two lenses are more similar than they are different. The obvious differences are the focal length zoom range, the widest aperture and the price. The focal length difference is noticeable - and the aperture difference is big. F/2.8 lets in twice as much light as f/4. Of course, you will pay twice the price for twice the light.
My 16-35 L is somewhat sharper than my 17-40mm L at most comparable apertures - especially in the corners. The 17-40 is a better close-distance lens and is slightly sharper at the long end. The 16-35 has less vignetting at f/2.8 than the 17-40 has at f/4 at all comparable focal lengths. The 17-40 has less barrel distortion at 17mm than the 16-35 has at 16mm. The Canon 17-40 L is insignificantly shorter (.3" / 6.2mm) and lighter (.2 lbs / 100g). The other image quality factors are very similar. All said, I consider the Canon EF 16-35mm f/2.8 L USM Lens a better lens - it is my choice for a full-frame ultra-wide lens. This is the lens I take when my ultra-wide results must count. However, if you do not need the f/2.8 aperture, the 16-35 may not be worth the "twice the price" factor to you.
Why do you need the wider aperture? Handholdability and action stopabiliity - To stop action and to hand-hold the camera/lens in lower light levels. I consider an f/2.8 lens to be the minimum aperture opening for shooting people indoors without flash has the main light - People are seldom motionless. Narrower apertures can be used indoors for motionless subjects, but you might need image stabilization or a tripod to get a sharp shot.
Another way to compare an f/2.8 lens with an f/4.0 lens is to compare the required ISO settings required to get equal exposures. As high ISO noise levels are reduced in our latest DSLRs, it is easier to live with an f/4 lens. Still, the difference between ISO 800 and ISO 1600 is noticeable - and the difference between ISO 1600 and ISO 3200 is big.
One of my primarily uses for the 16-35 L is available light group photography. Capture a family sitting around a dining room table or at a restaurant. Capture a large filled venue (church sanctuary, theatre ...) during a wedding, musical, play or other similar event. It works very well for parties such as large birthday parties.
Another use I frequently find for my 16-35 L is wide landscape photography. Use wide angles to emphasize an object in the foreground against an attractive (and mostly in-focus) background. Or use it to simply take in a very wide field of view.
Be careful if you intend to use this lens for portraits. The Canon EF 16-35mm f/2.8 L USM Lens makes a very good wide environmental portrait lens. Stand back and make a person part of a wide landscape shot. Or, move in close for a unique perspective on the subject. Unique perspectives can be fun, but don't overuse them (they get old). What I mean by unique - We don't typically look at people from really close distances. And when we look at photos of people from these distances, certain body parts start looking funny. As I mentioned above, wide angles emphasize foreground subjects. If someone's face is the subject, their nose (a feature many people want to hide) becomes the foreground - and is emphasized because of the close perspective. And the 16mm close-distance barrel distortion makes this matter worse (or better if you are going for "unique"). A 1.6x body user might find 35mm long enough for nice full body portraits.
Architecture and real estate photography often have large subjects that require wide angle lenses. These are many, many more good uses for the 16-35 L. You might need to remove the barrel distortion from 16mm shots during post-processing.
The 16-35 could be the solution for any other tight shooting space situation that is presented to you. Shooting in an airplane cockpit, the passenger's seat of a car, inside a large product ...
The 16-35 L is one of the best Northern Lights and night sky lenses available. If you are taking pictures of the night sky, shutter speeds need to stay at or below 20 seconds at these focal lengths to prevent star trails. This lens performs this task excellently.
The Canon EF 16-35mm f/2.8 L USM Lens could also make a reasonable walk-around lens if your needs lean toward a wide angle lens for situations in relatively confined spaces or for very large subjects. The short focal length range limits this lens' usefulness as a general purpose lens. But again, this lens performs excellently as part of a kit.