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.
As you page between the two shots it can be shocking to see completely new elements crash into the background of the second shot while the subject appears to remain the same. This exercise clearly shows how focal length combined with viewpoint affects perspective distortion. 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.
The photos were taken with my Nikon 18-200mm lens, the first image was set at ISO 400, FL 130mm, 1/80th @ f5.6. The image gives a greater feeling of space around the subject and also allows more of the background to be viewed. The second image feels more compact and was also taken at ISO 400, FL 65mm, 1/250th @ f5, the subject becomes the sole centre of attention with very little background to play around with.
Even though not the most photogenic person I would like to thank my daughter Casey for posing for me, even if I did have to bribe her.