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.
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 length 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 if view of your normal vision?
The above images are taken at 18mm, 35mm, 75mm and 105mm respectively.
18mm, 48mm, 85mm and 175mm.
18mm, 22mm, 44mm, 80mm, 155mm, 300mm.
Apart from obviously giving the sensation of moving through the frame / image and travelling towards a focal point the images also bring new objects into view.
The images at 18mm offer the most in terms of leading lines and depth and 35mm – 48mm feels the most natural view-point to what my eyes see. More features become apparent at 85mm and beyond however the image starts to grain at the longest focal lengths.