Digital Home Thoughts: Wide-angle to Zoom Photos with the Canon 17-85mm EF-S Lens

Changing Lenses
One of the advantages of the SLR design is removable lenses, allowing you to change the capabilities of the camera from tight close-up work to paparazzi super-snoop shots. This does, unfortunately, require you to carry more lenses and spend more money, which might go some way to explaining why my wife only ever bought one lens to go with her Canon film camera - a very nice Tamron 28-200mm lens that wasn't too big but gave a reasonable range between wide angle and zoom.

Canon have been smart with their digital SLRs and retained compatibility with all of the EF-format lenses. The downside is that, because of the differences between the 35mm optics and the smaller digital optics, a traditional lens gets scaled by about 1.6. This turned my wife's Tamron lens into an effective 45-320mm lens - great at the zoom end of the scale but rather lacking at the near end. We soon found out that taking close shots of flowers was not going to work with the Tamron.

Enter the EF-S 17-85mm f/4-5.6 IS USM Zoom Lens!
In order to compensate for the 1.6 magnification factor, Canon introduced a new format of lens - the EF-S lens. These lenses can only be used on compatible digital bodies such as the EOS 20D, 300D and 350D. Figure 1 shows the Tamron & Canon lenses from the perspective of the end that goes into the camera body.


Figure 1: Tamron & Canon optics

The 17-85mm lens reviewed here is equivalent to a 27-136mm lens on a 35mm camera and therefore restores the wide-angle range that we lost on the Tamron.


Figure 2: Tamron 28-200mm and Canon EF-S 17-85mm

Figure 2 shows the Tamron lens next to the Canon lens. As you can see, they are very similar in size, with the Canon lens being slightly longer and slightly fatter. The inclusion of image stabilisation is probably responsible for a lot of the size difference, but more on that later.

Lens Controls


Figure 3: Zoom and focus rings

The outer ring on the lens controls the zoom factor, while the inner ring controls focussing. Canon state that the lens can be used in "macro" mode, where you effectively lock off the focus at the lower end, put the lens into manual focus and, according to the lens manual, move your body backwards and forwards to get the picture into focus. However, the EOS 20D doesn't have any indicator of whether or not the picture is in focus, so I found these instructions very difficult to follow. I tended, instead, to leave the lens on auto-focus, frame the photo as I liked and then adjust how close I was until the camera couldn't focus any more, and then back off slightly to let the auto-focus do its work.

The end result is that you might not be able to get entirely the shot you are after, but the pixel resolution of the 20D means that you can crop the shot very nicely. Figure 4 is an extreme crop - if you click on the image, you might be surprised by the full photo :-).


Figure 4: Extreme close-up. Click on the image to see the full picture (3.2MB)

The control for switching between auto-focus and manual focus is found on the side of the lens, as you can see in Figure 5. If you have the lens set for auto-focus, it is still possible to use the focus ring to adjust the setting (although auto-focussing on the camera might then put that setting back). The Tamron lens, by comparison, complains quite audibly if you try to manually focus when the lens is on auto.


Figure 5: Lens switches

Below the AF/MF switch is the stabiliser option. When you turn on this feature, gyro-stabilisers inside the lens try to keep the image stable. This reduces camera shake to the equivalent of setting the shutter speed 3 f-stops lower than without IS turned on. There is a very slight noise when you are using the feature, but it isn't very loud. The camera is very clever about powering the feature - it turns on when you auto-focus and turns off a few seconds after the photo has been taken. Using the camera's battery to power IS will reduce the number of photos you can take.