On Jul 14, 2005, at 7:26 AM, Kostas Kavoussanakis wrote:
2) Circle of confusion (COC=a lens design parameter, different for
different
<snip>
For this reason, a 50mm lens used on APS format should show less
DOF than a
75mm on 35mm format (provided that both lenses are designed for
35mm and are
set on the same relative aperture).
Should that be "on the same absolute aperture"?
Since the notions of the physical size and f/number of the aperture
are so often misconstrued with the word aperture, I normally like to
use the nomenclature "lens opening" to indicate the physical size of
the aperture and "f/number" to indicate the aperture scale setting.
EG:
- A 50mm f/2 lens has a maximum lens opening of 25mm.
- The f/2 aperture setting allow the lens to transmit 2x as much
light in unit
time as the f/2.8 aperture.
Godfrey
