Find a scene that has depth. From a fixed position, take a sequence of five or six shots at different focal lengths without changing your viewpoint. (You might like to use the specific focal lengths indicated on the lens barrel.)
As you page through the shots on the preview screen it almost feels as though you’re moving through the scene. So the ability to change focal lengths has an obvious use: rather than physically moving towards or away from your subject, the lens can do it for you. The other immediate difference between the shots is the ‘angle of view’, which also depends on the sensor size of your camera. Use the sequence to try to get a feeling for how the angle of view corresponds to the different focal lengths for your particular camera and lens combination. Which shot in the sequence feels closest to the angle of view of your normal vision?
For this exercise, I took a few shots around Hucknall Train Station. For these shots I used a Canon 400D (crop sensor) with a 18-55mm kit lens set at ISO 200 and shutter priority 1/160.
The following shots were taken:
Image 1 – 18mm
Image 2 – 30mm
Image 3 – 37mm
Image 4 – 55mm
The image most closely resembling the view I could see with my eyes is Image 2 – 30mm. This focal length would be equivalent to 49mm with a full frame sensor.