Exercise: Focal lengths

Wide-angle shot (18mm, efl: 27mm) of the River Thames from Kingston Bridge. On the left you can clearly see the promenade and on the right, the tow-path. The rowers can barely be made out in the centre of the image, and neither can the boats moored alongside where the rowers are.

This second image is zoomed in to 40mm and shows a distinct difference to the 18mm shot. Around 25% of the image has been lost from the sides.There is much less promenade on the left of the shot but the tow-path on the right is still visible. The rowers (who are actually physically closer than before) can be made out much more clearly.

This shot is at maximum zoom for the lens I was using, 55mm. There is less of a difference between this and the previous shot compared to the difference between the first two images, but you can see that the gazebo is now at the left edge of the image. The rowers, who were the second set to pass (the first lone rower has already passed), can clearly be made out, even though they are in approximately the same place as the lone rower was in the 18mm image.

This image was taken with a focal length of 110mm (efl: approx 160mm)  The rowers and coach are are now alongside the yellow boat, which is itself now quite close to the left of the frame. These moored boats couldn't be made out in the 18mm image. the tow-path on the right has now been lost, but the promenade is now actually more visible.

For the final shot at 200mm (efl: 300mm) I shifted the focus point to the white boat in the centre left of the image. When you compare this to the 18mm focal length image, these moored boats can barely be seen, now they all but dominate the scene. The promenade is now quite clear and individual people can be picked out.