On 9/19/2011 7:34 PM, Paul Stenquist wrote:
On Sep 19, 2011, at 10:20 PM, Paul Stenquist wrote:
On Sep 19, 2011, at 9:46 PM, Larry Colen wrote:
On 9/19/2011 6:14 PM, Paul Stenquist wrote:
I find the essayist's snoopy metaphor silly and demeaning. And while he admits
to an Adams renaissance, t's clear that he doesn't understand the artistry of
Adams' work and how he was able to bend light in the darkroom to idealize a
scene. He seems dismissive of the zone system, a a way of working that
redefined photographic excellence. The writer continues to demonstrate his lack
of photographic knowledge in asserting that an f64 aperture results in both
optimum depth of field and clarity. Depth of field, yes. Clarity, no.
Doesn't that depend on the focal length? Whether you're using a 6mm lens on a
point and shoot, 30mm on an APS, 50mm on a 35mm, or 300mm on an 8x10?
Yes it does. But even on a "normal" 300 mm lens for 8x10, f64 is a small ap and
will cause diffusion. It's definitely not optimum in that regard.
Further research reveals that diffusion varies with format size, not focal
length. f64 on 8x10 is said to be approximately equivalent to f8 on 35 mm film,
so it's safe to day that diffusion isn't a problem at that aperture, yet it's
not necessarily correct to say that f64 produces optimum clarity. But this is a
small point. Overall, I felt that the essayist didn't demonstrate a firm grasp
of photographic principles.
Diffusion or diffraction?
It was my understanding that diffraction happens at any opaque edge
within a range that is determined by the wavelength. Therefore the
larger the aperture the smaller the percentage of it that will be
subject to the effects of diffraction.
f/64 on a 320 mm lens would be an aperture of 5mm, which would be the
same as f/10 on a 50mm lens or f/8 on a 40mm.
I suppose that it's possible that the angle of incidence of the light
beams hitting the aperture could affect the amount of diffraction, and
therefore it's not a linear function that diffraction becomes a problem
with apertures of 2mm or smaller in diameter.
It's also been roughly 30 years since I took a course in either physics,
or field equations, so I could be completely off base.
--
Larry Colen [email protected] (from dos4est)
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