The focal length of a foot?
Jun 2nd, 2010 by Keith Chaloner
‘Don’t be lazy, zoom with your feet’. I’m sure we’ve all heard or read that a few times, certainly several times during the past season alone. Not to be lazy is always good advice and the exhortation to ‘zoom with your feet’ would also be fair enough if the sole object of changing focal length is to adjust the size of an important object within the picture so as to sit well within the frame. But there is more to it than that surely. If one were photographing an essentially two dimensional subject it would be fine, but generally we – and especially landscape workers - are dealing with a subjects having great depth and are attempting to make them look that way on the flat, two-dimensional surface of a piece of paper or a screen. We are also striving to interpret the subject in our own individual way. This means that we have to resort to a range of tactics, not the least of which is to use perspective to our advantage. Just changing the focal length of the lens alone will not do that and neither will the use of a single prime lens, however far we walk with it (see footnote). Instead, we have to use our feet in addition to selecting a different focal length.
By way of an example, suppose I were trying to photograph a country house, using the stone piers of the open gateway to frame the subject, and I wanted to employ the sinuous driveway as a lead line with the main subject (the house) on, say, the top right hand third. Let us further suppose that with the gateway framing the subject, I find that the house seems too close to the gate and the drive appears to be foreshortened. To change this and to convey the grand scale of the subject, I must use a shorter focal length – but then I find that the gateway is no longer at either edge of the frame but now appears some way in, i.e. I have included a wider field of view but the perspective remains unchanged. To correct this I must then walk towards the subject in order to re-establish the framework of the stone piers in the preferred position and only then will I have achieved the composition I want with the altered perspective.
A further, and very well-known, example illustrating the significance of appropriate perspective is that of the tourist supporting the leaning tower at Pisa. Visitors will know that the ‘must take’ snap is that of one’s companion leaning and pushing with her/his hand to hold up the tower whilst looking towards the camera. Most tourists intuitively make a sensible decision about choice of focal length and relative distances between camera/poser/tower so that the poser is supporting the tower by a huge effort at perhaps a third of the way up. It would be less impressive if the poser’s apparent height were to be comparable with that of the tower when she/he could presumably support it with one finger. The resulting picture would be equally unconvincing if she/he appeared to be very short since, however Herculean the effort, pushing against the buttresses or base of the tower would be quite obviously futile.
In short - and although it is often helpful just to change the angle of view - to alter perspective, both focal length and viewing position must both be changed. Perhaps we should encourage each other with ‘Don’t be lazy, zoom and use your feet’?
Malcolm Bowditch
