Olympus E-3 User Manual page 12

units, the size of the image circle cast by the lenses as well as
the distance between the last lens element and the sensor itself
were all agreed upon and bound into a single standard.
telecentric
Key to top performance was a near lens design which
ensures that the light from the image always strikes the sensor
at, or as near as possible to, 90 degrees. This avoids vignetting
(the darkening of the corners of the image) which can be caused
by using older lenses designed for film use on a digital sensor.
Proof that this was a far sighted innovation is found in the fact
that modern top-end D-SLRs have dedicated software to process
images where vignetting has been caused through the use of
lenses not designed for digital imaging.
The benefits of near telecentric lens design for digital systems
as defined in the Four Thirds standard is shown in these
diagrammes
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