◗ Practical Optics: Testing Different Sensor Sizes Left: The focal length is changed in order to maintain Marion's framing at a fixed camera distance for different sensor sizes. Above: The diagram illustrates that longer focal lengths are required for larger formats. Below: The loss of depth of field with longer focal lengths is especially apparent when comparing the 45mm and 90mm, matched for this close-up composition in Super 35 and Super 16 formats. 10. Perspective and Focal-Length Personality These tests reveal the quality of perspective as modulated by camera distance. In optics, perspective describes the transformation of imaged objects with focal length and distance. Another way of saying this is that perspective describes the way a lens renders space, with an impact on: - how parallel lines are rendered - the magnification of background elements - the appearance of depth in the image - the portraiture of the face To me, angle of view and perspective define the "personality" of a focal length - what makes, say, a 24mm different from a 90mm. As noted earlier, you really need to see the camera move, or people move within the frame, to get a full appreciation of how a lens renders space. ➣ 96 April 2016