PEAK EXPOSURE
1
g
o to r a
Ronald Turnbull helps you get your head around the histogram
r • w ri t
P
hotographer Ansel Adams (I think it was him but it
could have been some other famous photographer,
the Outdoor Focus editor will know*) had a
principle of tones and shades. One eighth of the black-
and-white image should be black, one eighth should be
white. One eighth should be very dark grey, one eighth
should be very pale grey. One eighth should be quite
dark grey, one eighth quite pale grey. And one eighth
each of pale mid-grey and dark mid-grey.
Picture rights for Adams photos are pricey, so I insert
one of my own taken, where else, in the Ansel Adams
Wilderness. It’s the place where every image of Cathedral
Peak naturally falls into the Ansel shade arrangement.
Or does it? Today, the computer can do this for us
digitally, by graphing how much of my pic falls into each
of the shade ranges. We see that the distribution isn’t
quiet as Adams would have it. I have rather too much
pale-pale greys – that’ll be the lower sky. And I’m a bit
lacking in the mid-pale-grey zone.
In the cairn picture (right), the big spike represents the
middling-pale tones of the mist and sky. The small spike
at far left measures the darkest shadows, the unlit areas
of rock like those directly below the cairn. The other
small spike at the right is the sunlit snow. The histogram
reveals, what’s not obvious to the eye, that there are no
areas of pure white or even of near-white in the image.
So what’s it for?
In outdoor sunlight, it’s very difficult to tell from your
camera screen whether you’ve got the exposure or
not. In very low light, the brightness of the camera
screen can, contrariwise, convince you of a nice bright
image when it’s actually underexposed. A peek at the
histogram tells you straight away. Just supposing you a)
* It was Ansel Adams (with Fred Archer) who developed the Zone
System described above.
autumn 2018 | Outdoor focus 15