Before we can take a picture, we have to consider the subject we're photographing and the type of lens that will best capture that subject in a flattering way. It is important to know that the lens on front of the camera bends and refracts light as it enters the camera and strikes the sensor. The photographer can chose how much the light is bent and what the effect is on the subject by choosing the right focal length for the job.
This is a crazy cool animation about focal length that I found online when creating this presentation. I embedded it here for you all to see. This animation shows the difference between a 20mm (wide angle lens) and a 200mm (telephoto lens). Notice how the subject's nose appears larger or smaller in relation to his/her cheeks and facial structure. When the camera is wide the subject appears to have more distortion in his/her face. However, when the camera is telephoto at 200mm the subject's face fills out more and appears more natural as if we were looking at him/her face-to-face.
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