Have you ever wondered why camera lenses produce a circular image circle (in general) but sensors are rectangular? Of course the answer is mostly historical – the format of a 35mm photo is in 3:2 aspect ratio, a ratio that people have long known to work well due to human binocular vision.

But lenses, in general, are circular. they produce an image circle, a circle that, in general, allows the 35mm sensor to just fit inside it. You don’t want your image circle much bigger than this (except for tilt-shift lenses) because that makes your lenses heavier and more expensive.

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