A type of question is frequently posted at photography discussion forums that goes something like this:

Help me decide. I’m going back and forth between the IS and non-IS versions of Canon’s f/2.8 or f/4 70-200mm zoom lenses, but I want to get the best optical quality. Which one should I choose?

Wrong question.

Too often the writer is trying to categorize really fine lenses into categories of “not good enough” and “best,” and on the basis of the wrong criteria in any case. Let me pursue this Canon lens example a bit. (You can probably substitute examples from the manufacturer of your gear.)

It turns out that all four of these lenses are optically excellent and can produce images of the equally high quality. They also share the same excellent build quality. Trying to decide between them on the basis of quality is hopeless. Any differences there might be – with the emphasis on might – are almost certainly much smaller than those based on normal sample variation.

And “quality” is really not the basis for distinguishing among them anyway. If you look beyond the issue of optical quality, there are other factors that likely are significantly different – though here what is “better” for one photographer may be “less good” for another. The significant variables among these lenses include maximum aperture, whether or not they have image stabilization, size, weight, cost, and how these factors make a particular lens more or less suitable for an individual photographer.

The best lens for someone requiring a zoom in this focal length range for handheld shooting of active subjects in low light would likely be the f/2.8 IS model. On the other hand, this could be a very poor choice for a landscape photographer who often carries the gear on the trail in a backpack and usually shoots relatively static subjects from a tripod. This photographer might be better served by the f/4 non-IS version.

The bottom line is that the significant differences between high-end lenses like these are not so much in their “quality” as they are in the “qualities” that they provide and their usefulness for ones particular approach to photography.

(One reason I’m writing this is so that I can point a link here rather than re-writing the message every time I want to reply to this question in one of those forums. :-)
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