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Canon EOS Digital Rebel XSi/450D by Christopher Grey

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APERTURE AND DEPTH OF FIELD

When we refer to the “aperture” of a lens, we are speaking of an iris, similar to that in the pupil of an eye, that opens or closes to allow light to enter, striking the optic nerve and sending impulses to the brain that are converted to a visual image. A lens aperture works much the same, except it allows as much light to enter as we tell it to allow. Although our brains can automatically compensate for light or dark (a human with good vision is capable of seeing light as dim as a trillionth of a watt), if we tell the aperture to allow too much light for the ISO we’ve set the chip to record, the result will ...

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