moving on let's cover four technical terms that will come up a lot.
: The first is a
"stop". Stops are a photography reference to a measured amount of light
that is consistent throughout the range of light and in all equipment.
is shutter speed. This is how fast the shutter opens, exposes the
sensor to light and closes. The faster it moves, the less light the
sensor receives. Faster shutter speeds stop action but don't let in
very much light. Slower shutter speeds expose the sensor to much more
light, but moving objects will blur. As a general rule of thumb I
consider 1/500 the absolute minimum while trying to freeze action. I
try to keep it from 1/800 to 1/1250, and don't find added benefit in
going much faster, it's rarely if ever bright enough to warrant doing
so while shooting kayaking.
The size of the
opening in the lens. It is adjustable just like your shutter speed and
the second means of controlling the amount of light reaching the
sensor. The numbering seems backwards at first, because the smaller the
number, the larger the opening (letting in more light) and the larger
number is of course a smaller opening. Your maximum aperture will vary
depending on the lens, the chosen Aperture is often referred to as
F-stop or F plus Aperture number. For example F5.6.
Previously known as
ASA, ISO speed is the digital equivalent to film speed. This is
the third way of adjusting your exposure. Lower ISO speeds absorb less
light than higher ISO but retain better detail and less noise. As
a rule of thumb keep your ISO as low as possible for the situation. On
stop of ISO is from 200 to 400, or 400 to 800.
If a shot is under exposed you can either slow down your
by one stop, or open your aperture one stop, or speed up your ISO by
one stop. Choosing which to do is what's key. Doing any one of
these three will increase your exposure the same exact amount. For fine
tuning, modern digital cameras can adjust in 1/3, 1/2 or full stops
depending on user preference.
So we have our three methods of adjusting exposure, now
what is the right exposure? Any bright day on the river has a large
dynamic range. This means that there is a vast difference from light to
dark. Our eyes are amazing at taking in large dynamic ranges of light,
while cameras are quite limited. Traditionally digital cameras have
less dynamic range than their film counterparts, making shooting
whitewater with digital tougher to some degree. So if you can only
capture some of the dynamic range, what part do you want to capture?
The most natural look to the human eye is the classic "expose for the
right" technique. Welcome to the world of the histogram. Leave your
camera on auto and this is what you will generally see while shooting
whitewater where the dynamic range is too big. Look in the top right
and you'll see the labeled histogram.
Shot with Nikon D200 and Sigma 10-20mm @ 17mm.
The meter in the camera is trying to average out the whole
scene, and in doing so over exposes the water. The histogram is a graph
that shows the dynamic range that is covered by the camera, and where
the light is in that range. The left side is the dark, shadow end of
things. To the right is the bright side of things, like white water.
The most natural look for a scene where the dynamic range is too large,
is to adjust the exposure so the graph does not go past on the right.
It's ok if detail is lost in shadow, this looks natural to the eye, but
if it's lost in the highlights it looks "washed out" and unnatural.
Here is the shot as it was taken, the light is close to the right edge
of the histogram, but does not pass it. Note how the shadows do go past
the edge of the histogram. With a dynamic range this large you have to
lose some of the range on one end or the other.
Lose it in the shadows and it looks natural to the eye...
In the first example I used photoshop to make the original
over-exposed, but trust me, leave your camera on auto and this is what
you'll get in most circumstances. Now we know what we're trying to
achieve with the histogram. Every camera has one, turn it on so that it
pops up every time you review an image, or shows in live view.
Next Up: Getting the right
#2: What is the right exposure?
#3: Getting the right exposure.
Photography Tutorial #4:
Low Light Action
Photography Tutorial #5:
Photography Tutorial #6:
Photography Tutorial #7:
Photography Tutorial #8: Wide Angles
Photography Tutorial #9: Panning
Photography Tutorial #10: Post-processing
Photography Tutorial #11: Sequencing