Re: Diffrection limit for APS-C DSLRs

On Tue, 21 Jul 2009 13:56:51 +0100, Martin Brown
<|||newspam|||@nezumi.demon.co.uk> wrote:

Reminding the Morons wrote:
On Tue, 21 Jul 2009 08:43:18 +0100, Kennedy McEwen <rkm@xxxxxxxxxxxxxxxxxx>
wrote:

In article <c32a659j3i4oui16bt9rb15psj98e78v10@xxxxxxx>, Reminding the
Morons <rtm@xxxxxxx> writes
On Mon, 20 Jul 2009 10:10:07 -0700, Paul Furman <paul-@xxxxxxxxxxxxx>
wrote:

Morons wrote:
Make sure to take the small-sensor camera's focal-lengths being only 1/6th
of the same needed for a DSLR for the same FOV into account to make your
calculations accurate. Diffraction spreads as a linear function of distance
from aperture to recording media.
That makes no sense, f/stop is focal length divided by aperture diameter
so it scales up and scales down. Unless your 'aperture' is diameter of
the opening, in which case: doh!


Of course it doesn't make sense to the brain dead. It doesn't scale up and
down equally by aperture alone.
Hey brain dead moron, he didn't say that, he said it depended on
RELATIVE APERTURE, ie. f/#.

You still have the physical distance which
MUST be taken into account.

That is precisely what he said - the distance involved is the focal
length, since that is the distance that the physical aperture is from
the focal plane to produce an in-focus image of an object close to
infinity. The ratio of focal length and physical aperture size is the
f/#.

Let's say you have an angular spread of 1-degree from the origin (the edge
of your aperture in this case). You project that onto a surface 1 ft. away
from your starting point. Now project that 1-degree spread onto a surface
across the room. Which surface is going to show more spread? This is how
diffraction works!
That's only part of how diffraction works!

It is independent of the aperture, per se.
No it isn't. The amount of angular divergence caused by diffraction is
inversely proportional to the aperture size. A smaller aperture
diverges the light over wider angles.

It depends
more solely on distance.
No it doesn't. The projection of the diverging light over a surface is
proportional to the distance of that surface from the aperture.

BOTH aperture and distance have EQUAL and inverse effects on how much
the light spreads over the surface. Increase both the aperture and the
distance by the same amount and the amount the light spreads on the
surface stays EXACTLY the same.

f/# is the ratio of that distance to the aperture!

Do none of you know what diffraction really is? I'm starting to think so.
The above, projecting a point-source of light onto a razor's edge is a 1st
year's physics experiment. Physics 101.

That is diffraction from an edge. This is diffraction through an
aperture. The two are related but NOT the same. Diffraction through an
aperture is a rotationally symmetric variation of diffraction through a
slit - which is two OPPOSITE edges. The diffracted light rays from each
side of the slit (or opposite sides of the aperture) interfere,
destructively in some cases, constructively in others. The intensity of
the diffraction pattern through an aperture is simply the interference
sum of all the rays through the aperture to any point on the image.
Physics 101.

Thanks for showing everyone what a perfect idiot you are.

Kennedy is correct it is you who are the ill educated Moron.

Why do you think that we make large aperture telescopes to obtain high
resolution images? The focal ratio or photograhic f-stop number is what
determines the diffraction limited length scale on the sensor at focus.
The diameter of the aperture determines the maximum angular resolution
that is possible if the system is truly diffraction limited.

The angular scale for diffraction at a circular aperture is
1.22lambda/D
and after multiplying by the focal length the point spread function for
a lens focussed at infinity is
1.22lambda*f/D

The laws of optics are well defined. The linear scale of the point
spread function at focus depends on the focal ratio. A reasonable
description of diffraction as it applies to photography is online at:

http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

It even deals directly with Morons clueless misunderstanding.
(see the bottom paragraph)

Regards,
Martin Brown

LOL!!!!!!!! Citing the main and most often misleading website that has
consistently explained it wrong all these years. GOOD GOING! LOL!!!!!!!!

Idiots parroting idiots. I love it!

ROFLMAO!

.

Relevant Pages

  • Re: Diffrection limit for APS-C DSLRs
    ... Reminding the Morons wrote: ... Diffraction spreads as a linear function of distance ... from aperture to recording media. ... That is precisely what he said - the distance involved is the focal length, since that is the distance that the physical aperture is from the focal plane to produce an in-focus image of an object close to infinity. ...
    (rec.photo.digital)
  • Re: Diffrection limit for APS-C DSLRs
    ... Diffraction spreads as a linear function of distance ... f/stop is focal length divided by aperture diameter ... year's physics experiment. ...
    (rec.photo.digital)
  • Re: Diffrection limit for APS-C DSLRs
    ... Diffraction spreads as a linear function of ... f/stop is focal length divided by aperture diameter ... since that is the distance that the physical aperture is from ... year's physics experiment. ...
    (rec.photo.digital)
  • Re: Diffrection limit for APS-C DSLRs
    ... Diffraction spreads as a linear function of distance ... f/stop is focal length divided by aperture diameter ... year's physics experiment. ...
    (rec.photo.digital)
  • Re: Diffrection limit for APS-C DSLRs
    ... Diffraction spreads as a linear function of ... f/stop is focal length divided by aperture diameter ... since that is the distance that the physical aperture is from ... year's physics experiment. ...
    (rec.photo.digital)
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