Select your longest focal length and compose a portrait shot fairly tightly within the frame in front of a background with depth. Take one photograph. Then walk towards your subject while zooming out to your shortest focal length. Take care to frame the subject in precisely the same way in the viewfinder and take a second shot. Compare the two images and make notes in your learning log.
I wanted to see the effect of different focal lengths so took four shots with my 300 – 16 mm zoom lens:
Perspective distortion is actually a normal effect of viewing an object, for example where parallel train tracks appear to meet at the horizon. A ‘standard lens’ – traditionally a 50mm fixed focal length lens for a full-frame camera (about 33mm in a cropped-frame camera) – approximates the perspective distortion of human vision (not the angle of view, which is much wider). A standard lens is therefore the lens of choice for ‘straight’ photography, which aims to make an accurate record of the visual world.
Certainly the focal length combined with viewpoint distorts perspective, this is apparent in both the background and the subject (especially of course at 16mm). I had not appreciated the amount of distortion that occurs with a change in focal length and will be careful not to zoom too much from a distance when photographing portraits, something that I may be inclined to do when taking “street photography” shots to avoid getting too close to unknown subjects. I will have to learn to be bolder as I can see that moving closer to the subject will give a truer image.