“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.”
This was an interesting exercise, not least because of the unexpected dizziness from walking and zooming at the same time. It was another moment of frustration with my entry-level zoom, which has a different minimum aperture at the wide end to the narrow end, and which caught me out again. I’ve now bought a lens with a smaller zoom range but a constant aperture at all focal lengths. I couldn’t frame the two images exactly the same way, and I also managed to shift position so that the window is visible in the wider shot. Another issue is that I use a cropped sensor camera so 18mm is closer to 29mm, which is not wide at all.
I don’t enjoy making portraits with a long zoom, the available settings always seem to be a compromise and I prefer to work with primes where you make a setting and it stays put. I also prefer to use my camera in manual mode. I’m hoping that the new zoom will give me higher quality images with a workable range, so I can then forget about the kit and get back to the photographs.
So not my best results. The left hand photograph is not straight, and I didn’t want to straighten it in case I lost too much of what makes it a zoomed image. You can see that there is a much wider perspective on the image taken at 18mm with me almost in Clare’s face. The image taken at 135mm has less showing to the sides and above Clare, and the background is more blurred. Somehow one image is at f5.6 and the other is at f5, I was sure that I was in AV mode and that I didn’t change the settings, but I can’t see any other at to account for the difference given that I was manually setting the ISO too and that was the same for both images. I think I should reshoot this pair, somewhere with better light.