Re: Congratulations Canon for the 5D "Best Professional Camera" at TIPA

On Thu, 27 Apr 2006 10:40:56 GMT, ½ Confused
<somebody@xxxxxxxxxxxxxxxxx> wrote:

On Wed, 26 Apr 2006 21:26:23 -0400
In message <sa7052hlojl0v4cg2401huc3hqejbp1itv@xxxxxxx>
Rich <none@xxxxxxxx> wrote:

He said lenses don't vignette unless near wide open. I showed him
proof that they can vignette when not near (f4.5 lens stopped to f8)
wide open.
Wide open means wide open. Near wide open means what?
Say the lens is an f2.8. Would "near" wide open be f4 or would it
extend to f8?

FWIW... the only "fall off" I've noticed at 17mm (wide open at F4) and
24mm (wide open at f2.8) is what the eye sees as light changes over
such a wide area. One funny optical illusion I noticed was a colorful
room with a window on the right wall (relative to the camera
position). The upper left corner had light falling off, and the lower
right corner had light falling off. Well, the area below the window
on the right DID have light falling where the corner of the frame was
located (ie accurate exposure). The upper left ceiling corner was
accurate also... there was no direct window or electric light up there
and the result was a darkened corner in a photo of a darkened corner.

If there is a minor lighting problem I haven't encountered in my short
time with the camera/lens combination, it's going to be cropped out at
print time anyhow. Regardless, I too would like to have Skip and his
wife weigh in on this one... they are using it the most under various
conditions in a commercial environment and delivering prints to
clients weekly.

I need to upgrade DxO to the YouFinallyGotAFullFrameSensorCamera
version... if there is a natural fall off, it should be noticeable in
their corrections (assuming they have the camera+lens combination 100%
accurately modeled).

Jeff

Light fall-off is most apparent when shooting broad expanses of blank
areas that are underexposed or dark to being with. Thats why if
you shoot a picture of a deep blue sky it is more apparent than if you
give the image some more exposure.
But fall off is due to one thing only, the inability of the lens to
fully illuminate the entire frame. It can be remedied by using a lens
that has a larger circle of illumination than the sensor area and this
avoids the fall off. Unfortunately, for cost, size, etc, other
considerations, camera companies only build the lenses to "just" cover
the frame which means you experience visible attenuation at the
corners. There may also be a contribution to this when using older
SLR lenses on digital cameras. But, if you were to slap a medium
format lens on a 35mm camera, you would avoid the effect because the
circle of illumination more than covers the 35mm frame..
.

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