I was looking for a lens to rent, to photograph some migrating snow geese at nearby fields. I tried to find a Canon 400/5.6L lens, which Arthur Morris calls his "workhorse lens", and when that was unavailable, and the 400/500/600 lenses with larger apertures were prohibitively expensive, I turned to the more reasonably priced Canon 100-400/4.5-5.6L IS USM lens. My initial reaction when I first held the lens was "Gosh, this lens is small and light!". My perception rapidly changed in the first few minutes of handholding it in my living room. It is fairly long at the 400mm setting and quickly felt heavy. A tripod collar makes it easy to mount the lens and rotate for verticals and focus is surprisingly fast, smooth and slient. At the 400mm setting, the camera had some trouble auto-focussing, under low light. The workaround was to zoom to around 350mm setting and auto-focussing before zomming to 400mm to try autofocus again. That worked! The camera's infra-red focus assist beam is useless because it falls on the body of the large lens. Perhaps using a Speedlite flash and selecting the center focus point would have helped because its infra-red focus assist beam will then be employed.

Engaging and disengaging IS was audible with a faint 'clank' within the lens. The lens has two IS modes - mode 1 for regular shooting where the image is stabilized on both vertical and horizontal axes and mode 2 for panning, where the image is only stabilized on the vertical axes. At the 400mm setting, you can really see IS at work; without IS engaged, the image distinctly shakes in the viewfinder. By turning on IS, the image distintly freezes in the viewfinder. There is a ring on the lens to tighten friction on the zooming mechanism and tightening this ring is highly recommend whenever the lens might be angled downwards for photographing subjects.

The Popular Photography magazine ran a test on this lens and it recommended f/8 as the optimum aperture for this lens at 400mm, although f/5.6 seemed to have maximum sharpness. For photographing birds, I mostly handheld this lens at f/5.6 at the 400mm setting, using Fujichrome Provia 100F for maximum shutter speed. This lens employs a flourite and super-UD elements for controlling chromatic aberrations and a floating element for maximum sharpness at all focal lengths. Watch out! The all-metal construction will quickly cause your hands to freeze while using this lens outdoors in cold temperatures. There is a focal distance limiter button on the lens and it came in very handy while photographing groups of birds. Without restricting the focal distance, the camera would repeatedly hunt for focus when a bird slight moves out of the focussing rectangle. It was a bit difficult to operate the controls on the lens with gloves on, since they were small and flush with the lens body.

Tips on Bird Photography

Overall, this was a wonderful and affordable lens with sharp and crisp images even at wide open apertures at 400mm setting. Ernst Wildi writes in his book "Achieving the Ultimate Image " that one should not be concerned about image sharpness with a professional quality lens, at both ends of the aperture ranges. While the 400mm setting is not close enough for 'real' wildlife photography, you will find this lens very valuable on hiking trips, given its relatively light weight of just around 3lb. With the IS feature affording atleast an extra two stops of slower shutter speeds, you might be able to do away with your tripod on your next hike.