How does focal length affect perspective?
A. It doesn’t; it is subject distance that affects perspective. However, a longer lens provides more subject magnification at a given distance, so you can get farther from your subject without having the image be too small. By moving back, you make the magnification ratio between the front and back of your subject smaller, because the distance ratio is closer to one. So, in a portrait, instead of a nose that’s magnified much more than the rest of the head, the nose is magnified only very slightly more than the rest of the head, and the picture looks more pleasing. You can get the same perspective with a shorter focal length lens by simply moving back, and enlarging the central portion of the image. Of course, this magnifies grain as well, so it’s better to use a longer lens if you have one. Q27. What is “MTF”. A. MTF is an abbreviation for Modulation Transfer Function. It is the normalized spatial frequency response of film or an optical system. The spatial frequency is usually measure
