A bit of background
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\nEarly optical or photographic devices (such as the camera obscura) were little more than a simple opening – sometimes with an equally simple lens – that would allow light to pass through, the goal being to generate an image circle broad enough to cover the area required.<\/p>\n
Notice ‘image circle’ – given the physical properties of light, when it passes through an aperture (i.e. opening) it will reform the image as a circular image element; we simply crop this down to a rectangular image for convenience, partly because the image circle will not be sharp or bright to the very edges, nor are circular formats consistantly useful: <\/p>\n
Full article and further comments:
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\nSensors – does size and type matter? by Think Camera
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