"oj" wrote:
Celcius wrote:
Why is the sky washed out while my wife with a point and shoot gets blue
skys?
....
While everyone is intent in pointing out the sky is overexposed, they
For a reader with sufficient experience, pointing out that the
sky is over exposed tells pretty much the whole story. Of course
if the whole significance of a washed out sky is *not*
understood, then it isn't half enough of the story!
However, you have pointed out something that, at least to techie
types, is even more interesting. Newer cameras might use
computer analysis of the data to automatically adjust exposure
in much the same way that a photographer would... or not,
depending... :-)
That confuses the issue, because instead of getting the results
one would expect from a simple metering system, the results are
what one would expect when the photographer chooses some rule of
thumb to compensate for a simple metering system.
missed the point of the question, and I've thought the same thing
sometimes. I can point my old Canon Powershot P/S at a scene, and the
sky is blue and white shirts aren't overexposed, but my DSLR doesn't
seem to be able to capture the same range. Either the sky is blown
out, or the subject is dark.
Weird, huh.
Nah, just the expected results of the toys we like to play with!
Back in the good ol' days, Through-The-Lense light meters were
simple and there were just three kinds. It was either 1)
average a reading from the whole screen, or 2) from a small spot
on the screen, or 3) use a weighted response that gave more
emphasis to some known area, like the center.
With that kind of a meter we can set the exposure for the whole
scene, for example, but the bright sky will skew the average and
cause the desired part of the image to be in deep shadows. That
will still work /if/ the photographer manually sets Exposure
Compensation to +1 or +2 in order to cause more exposure. Hence
you get your "Either the sky is blown out, or the subject is
dark."
Another way is to use a spot meter or weighted area to eliminate
or greatly reduce the effects of the bright sky on the metered
value. This is essentially just another manual method of
correcting the exposure as above, and the results are typically
the same.
Given the above, an older or less complex camera when simply
pointed at the scene and the shutter released, will under expose
the shadow areas and allow for at least some texture in the sky,
which would allow it to be blue. (The OP's wife's P&S...)
However, a modern DSLR might well have a much more complex light
metering system, and will make the manual corrections described
above automatically! Instead of averaging the entire screen or
just a spot or some set weighting pattern, the meter might take
readings from several spots in the scene, do a computer analysis
to decide what is appropriate, and then adjust the weighting
pattern to match what it assumes the image most likely is.
In this case it can tell that 1/2 of the upper part of the image
is very very bright (it might even know it is blue!), while the
rest seems to be just the right amount less to be a shaded area.
In particular the center appears to be a shaded area. The
camera's computer program decides this is a sunlight scene with
bright sunlight and deep shadows with a lot of sky. So it
compensates by calculating the exposure based *only* on the
lower half of the image... which results in totally washing out
all of the sky, but providing a fairly good exposure for areas
in the shadows in the center of the image.
Don't want that? Use spot metering or turn off the
"multi-segment" metering mode to get a full scene average, and
use your own Exposure Compensation to get the exposure desired.
--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)