diffractive optics

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In some of my posts, such as the one about the Best Lenses for Travel and Humanitarian Photography, I venture to suggest a good single lens for travel. My recommendations have typically been the Canon 18-200mm f/3.5-5.6 or the more expensive Canon 24-105 f/4L. Both offer a useful focal length range for travel, image stabilization, and excellent image quality (relative to their price, of course – the professional L lens is of much higher quality). The 24-104mm also boasts the fast and quiet USM focusing motor.

One lens that I have previously failed to mention is the unique Canon 70-300mm f/4.5-5.6 DO IS USM lens. Its broad focal length range, image stabilization, and USM focusing motor with full-time manual focus* are all appealing features. (*you can over-ride or tweak the autofocus with a twist of the focus ring without switching to MF.) But what makes it a potentially great travel companion is its size and appearance. Due to its use of Diffractive Optics (the DO in its name) the lens is relatively small and light. And in addition, its exterior is black rather than the white of the L lenses. Thus it becomes a much more portable and much less obtrusive lens than the big, white 70-200mm and 70-300mm L lenses.

Canon 70-300mm DO lens diffractive optics
The unique green band of the Canon 70-33mm DO lens

The 70-300mm DO declares its uniqueness with a green band around the front of the barrel, where the red band of the L lenses sits. Diffractive Optics is a technology developed by Canon to reduce lens size while maintaining image quality and eliminating chromatic aberrations, and currently only two Canon lenses use DO. This lens has been around since 2004, and has overall received excellent reviews. For a professional photographer it will never quite replace a 70-200mm or 70-300mm L lens due to its slightly lower image quality and sharpness, and lack of the f/2.8 or f/4 maximum aperture throughout its full range, but for those just a little less demanding it could be the perfect travel companion for photographers not wishing to carry around a larger and more noticeable white lens.

Canon 70-300mm DO lens diffractive optics

There are mixed reviews on its sharpness. Some users claim it is sharp as can be, some say it loses sharpness at certain focal lengths and apertures, and other say with standard post-process sharpening there is virtually no difference between it and an L lens. One complaint that can’t be denied is its propensity for lens creep. Due to the weight of the lens elements and the fact that it zooms externally (unlike the internal zoom of the 24-105mm or the 70-200mm lenses) the zooming barrel will move on its own when pointed up or down. The lens has a locking switch for storage or for walking around, but otherwise it is going to creep. This DO lens also does not have a rubber weather-sealing ring at its mounting base, which is disappointing for a lens in this price range.

Optically the 70-300mm DO displays a couple unique characteristics as well. At certain apertures a hazy, often described as dreamy, outline will appear around bright out-of-focus areas. And due to the concentric circles of the DO optics (visible in the lens just by looking at the glass at an angle) out-of-focus spots of light also contain concentric circles, or “targets,” as shown in the image below. These rings also appear in areas of flare, so it is best not to use this lens if you are a fan of shooting into the sun to achieve purposeful lens flare.

Canon 70-300mm DO lens diffractive optics bokeh target bullseye
The interesting bullseye/ target bokeh of the 70-300mm DO lens, pronounced when at narrow apertures (f/16 here) – click image to view larger on Flickr.

The above image is a crop from the one below. Notice that in addition to the concentric circles, the bokeh of bright light spots becomes hexagonal at narrower apertures (like f/10 or f/16) as shown below, but it is nice and circular starting at f/8, without the targets being so pronounced at wider apertures (like f/5.6).

Canon 70-300mm DO lens diffractive optics bokeh
Canon 70-300mm DO lens – hexagonal bokeh with bullseye targets seen at f/16 – click image to view larger on Flickr.

So if you are looking for a high quality lens for travel with an exceptional telephoto zoom range, you may wish to consider the 70-300mm DO. It is not everyone’s ideal single lens for travel because its focal length starts at 70mm and thus lacks the wide angle range, but for those who like to zoom in close and capture faces and details, it could be a lens that stays on your camera much of the time. And even for those who already have a big, white 70-200mm lens, this could come in handy in many situations which you wish to be a little more discreet or even appear less intimidating to your subjects. Go to the store and play with one, and I think you may find that you love the size and feel of this lens, and can envision its great travel potential.

See and purchase the 70-300mm DO lens at Amazon.com

Have a look at some other reviewers’ posts to learn more about this lens, its technical specs, and its performance, as well as see images comparing its size to other lenses:

Review and description with size/ weight comparisons at The-Digital-Picture.com

Review focusing on image quality at Photo.net

Field test and very technical review at Luminous-Landscape.com

Canon’s explanation of Diffractive Optics