Cropping: In-camera vs. post-processing

Cropping, the name given to discarding unwanted parts of a photograph is perhaps the oldest post-processing action, possibly as old as photography itself!

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Here are some of the important reasons why it is needed-

1. To improve the composition for example, if your picture has a centered subject and you want it as per 'rule of thirds'.

2. To remove excess background as it is done frequently in street photography to remove unwanted clutter.

3. To alter the aspect ratio, for example, change the default of 3:2 to 16:9 to suit the display of an HDTV.

4. To make the subject more prominent (enlarge it, relative to the surroundings), a process often used by wildlife photographers.

Of these, the first two are done inevitably in post-processing whereas the latter two can be done likewise or within the camera before the picture is taken. In this article, we will concern ourselves more with the last type of crop which is popular with wildlife photographers. Here, photographers use only a part of the sensor and when they do so, the well-known (Picture 1) 'cropping factor' comes into play and will reduce the angle of view (AOV). The AOV will become narrower thus giving the impression of an apparent increase in focal length. At this point, it must be emphasized that once a lens is designed, and manufactured, its focal length cannot change. However, the AOV changes and in general becomes narrower when smaller or a smaller part of a sensor is used. More of that later.