- Posted by Jon Tarrant
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Zoom lenses and composition
Although I wasn't talking about zoom lenses at the time, in my last ‘blog I pointed out: "The biggest effect of focal length is on perspective - because perspective depends on the distance from which an object is photographed. In other words, a 100mm lens will cover the same image field as a 50mm lens when the former is positioned twice as far away from the object as the latter. But when the camera is twice as far away, the relative distances of a three-dimensional object vary less than they would close-up: this in turn affects the way in which the object is rendered even though the overall image field is the same." (I actually got my "latter" and "former" the wrong way around previously and have therefore corrected it here!).
This needs a bit more explanation because zoom lenses combine a range of focal-lengths, so what is the best way to decide on the ideal setting to choose? Many people still think of wide-angle (short focal-length) lenses as a means of getting more into a picture so simply reduce the focal-length when using zoom lenses so that "everything fits in the picture". That tactic applies only if the photographer maintains a constant position, in which case a shorter focal-length setting will indeed squeeze more into the picture and a longer focal-length will crop into the scene to record only specific areas of the wide-angle frame.
When zoom lenses first started to become popular in the late 1970s, with optics such as the much-praised Tamron 70-210mm, it was common to hear fans of prime lenses advocate: "The best zoom lens is the pair of feet on the end of your legs". Some of those people may simply have been Luddites but others were expressing the often-cited belief that primes lenses offered better image quality - and in general that statement is still true today.
In addition to these two considerations there is a third reason to express the "zoom feet" opinion: this comes from the wisdom that recognises the effect of shooting position on image perspective. For the reason repeated above, there is a huge difference in appearance between a picture taken using, for example, a 50mm lens close to an object and one taken using a 100mm lens from twice as far away. In other words, zooming the focal-length from a fixed position gives a very different result from recomposing the picture either closer or farther away.
So leaving aside image quality, we have both the flattening effect of the shooting position and the angle-of-view of the focal-length to take into account when using zoom lenses. Whereas image quality is a technical, objective factor, "flattening" and "angle" are creative tools that should be chosen and used after careful thought.
I venture to suggest that the majority of people who take pictures (although probably not the majority of those reading this ‘blog) think nothing about perspective and care only about "getting everything in". And that is a shame because it suggests that one of photography's greatest tools has been side-lined in the rush towards greater convenience.
So here is my suggestion for a photographic activity - either for individuals or as a camera club outing in the summer ahead... Fit a prime lens or simply set a zoom lens to one focal-length and spend a few hours looking at the world in a simpler way... moving backwards and forwards in front of an object or scene to determine the ideal position from which to photograph it. I agree that this will probably slow things down a bit but most things benefit from a little bit more time and thought: photography is no exception!