It’s no surprise newcomers to photography get confused when so much of the received wisdom they hear is not quite right. Alongside “aperture controls flash, shutter speed controls ambient” this is one of the most ubiquitous myths that do the rounds. The converse is also untrue: wide angle lenses do not distort (at least not because of the focal length, they may of course have defects in their design and manufacture).
“But” I hear you say “if I take a picture of someone with a wide angle, their features look all distorted, they have a big nose and their entire head looks like a football! If I use a telephoto lens, they look much more natural.”
The 35mm image has been cropped to render Gary’s face the same size as the 200mm one for comparison. Despite being shot at two very different focal lengths, they look exactly the same. This is because the real factor that produces compression or distortion had not changed: I shot both pictures from the same distance away from Gary. It’s the shooting distance that determines the “compression factor” or conversely, the distortion we blame wide angle lenses for. We associate compression with telephoto lenses, because when we shoot from further away (which actually causes the compression) we naturally tend to be using a telephoto focal length. When we shoot from close in (which causes distortion of facial features) we have to use a wide angle lens to get the whole subject in. Thus, we associate compression with telephoto lenses, and distortion with wide angles.
Here’s the 35mm shot from the two images above, with another, also at 35mm but shot much much closer, this time un-cropped, as I’m close enough to fill the frame at 35mm:-
Ignore the lighting differences. Gary has moved forward a bit relative to the soft-box off to his left, which has produced more shadows on his face. Look at the nose, and ears. The nose gets bigger, and the ears are smaller and are hidden by the head. So how is it that the shooting distance has such an effect on the image? Well it’s a bit like the inverse square law that governs the intensity of light (or any radiating energy) over a distance. When you light something real close, the light falls off quickly, as the difference in distance between 2 points on the subject from the light source is large. The same applies for distance to camera from two points on the subject. Lets consider the nose and the ears in profile. Looking at the head in profile, say the distance between the tip of the nose and the middle of the ear is 10cm. If I shoot the picture at 4 metres (400cm) away, this is a 2.5% difference in distance to camera. The ears are 2.5% further away. If I shot the picture at 0.5 metres (50cm) then the ears are 20% further away than the nose: a much more significant difference.
Just like the inverse square law for light, the resulting change in size (area) of objects over distance is also an inverse square function. If an object moves twice as far away, it will be a quarter of the size (area). Here’s the un-cropped 35mm image taken from the same distance as the 200mm image was taken.
Given the difference me moving closer to Gary has made to his portrait whilst keeping the focal length the same, you should also realise that you cannot “zoom with your feet”. I’m all for using fixed focal length lenses (so called “prime” lenses) as a device to encourage more creative thinking about composition, framing and looking for the shot and so on, and yes: due to their simpler construction, they are very often a bit sharper than a zoom, however this rather glib phrase that often follows in the discussion of prime versus zoom, is nonsense. If you move closer rather than changing your focal length, you will dramatically alter the picture, perhaps to the point where it no longer works. On the other hand, it may be an even better picture, but the point is, it ain’t the same picture. Zoom with your zoom ring. Move closer with your feet. They are not the same thing.