Lenses & perspective

Changing focal length or zoom setting changes the magnification, but it also has other effects

Each month we’ll set an assignment to help you turn theory into practice. To recap, when you change your focal length, you’re also changing the angle of view. At a short focal length of 18mm, you can fit more of the scene into the frame, compared to using a long focal length of 200mm from the same spot.

However, focal length isn’t merely a simple cropping tool – it also has other creative effects on your picture. For instance, it indirectly affects perspective. Photographing subjects up close with a wide-angle lens makes foreground objects look larger, while using a telephoto at a greater shooting distance creates a compressed perspective, making things at different distances appear closer together. Focal length also affects depth of field, which you can use to great creative effect, as we’ll investigate in the near future.

YOUR ASSIGNMENT

See the effect that different focal lengths have on your resulting image with these tests:

Without moving your camera or subject, take three shots at three focal lengths. For instance, try 18mm (wideangle), 35mm (‘standard’ on a DX camera) and 100mm (telephoto). You should see, as you might expect, that the magnification and angle of view change according to the focal length that you’ve set.

Now take three shots of the same subject at different focal lengths – 18mm, 70mm and 200mm, say. This time, change the camera position and move back each time so the subject still fills the frame. Below are examples that show the effect this has on the perspective and how you can use this to change the style of the picture…

18MM FROM 3M

At this focal length, you have to get right up close to the subject (the flowers at the base of the monument). This exaggerates the distance to the building behind, making it look much smaller.

70MM FROM 10M

At 70mm, you have to move much further away from the subject. Relative to the camera, the flowers and the building now seem to be much closer together, and the building appears larger.

200MM FROM 29M

At 200mm, you have to move so far away from the subject that the background looks not much further away – hence the ‘perspective-flattening’ effect of telephoto lenses.