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Lecture 15: Cameras & Lenses (14)

The focal length is supposed to refer to the distance between the image plane to the optical center of a camera lens. This would probably be a very important concept in photography in general, so what are ways that photographers have to optimize different focal lengths to get the correct field of view for their picture?


@rishiarjun it is certainly quite important in both photography and videography! This GIF does a great job showcasing the effect focal length can have.

Usually when we compare focal lengths, we just see a zoomed in or widened image. However, in this GIF the photographer backs the camera away to keep the sizes exactly the same. This shows how a longer focal length can 'compress' the depth of an image, and make distances look flatter. This is why portrait photographers always use 85mm equivalent focal length lenses.

Similarly, I mention "equivalent" because different sensors will have a different equivalent focal length depending on the sensor size. For example, a Micro 4/3rds sized sensor is smaller than the standard size, which means a standard lens would project the center of the image onto the sensor. So a standard lens would look more zoomed in on this sensor. This means that it can be rather difficult to get very wide shots on smaller camera sensors as the lens itself will need to be extremely wide.

Similarly, cameras with really large sensors like the Alexa 65mm can allow directors to shoot really wide much easier, and also throw on bigger lenses to improve things like DoF.


Focal length is an important concept for why people often do not like how they look in selfie photographs! It's all to do with focal length (and sometimes image flipping)

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