Do a noise test
What is surprising to me is how often people are surprised by
the amount of noise in their images. They crank up their ISO
speed to 1600, shoot at 1/4 second, and are surprised by the
amount and size of the noise. If you like to shoot available light
images—and we have to assume that you do, or you wouldn’t
be reading this book—one of the first things that you should do
with a new camera is make a noise test. Don’t freak out. It won’t
take long and the information will be invaluable.
Set up a situation that will produce longer-than-normal shutter
speeds and use high ISO speeds. Don’t use just one ISO—shoot
at 400, 800, 1600, and whatever else your digital SLR can
produce. Be sure to bracket exposures. Even though digital
capture is not subject to exposure shifts under slower shutter
speeds, bracketing exposures might tell you that slight over- or
underexposure in a given lighting condition might increase or
decrease the effect of digital noise. Be sure to include a known
color target such as a Macbeth ColorChecker (
www.gretagmacbeth.
com). Color won’t usually shift, but it provides some smooth
patches that will show noise better than textured ones, and there
are cameras whose color fades as ISO increases.
Open the files and use your image-editing program’s magnifying
tool to look at the noise and determine the optimum settings to
produce the least amount of noise. Take your time and compare
over- and underexposed examples. Although this process won’t
eliminate noise, it will make you aware of what switching from
ISO 400 to 800 will cost you. You may be able to live with the
amount of noise, but if you can’t, you’ll now know that you’ll
need a tripod so you can use a lower ISO speed. Be aware that
longer shutter speeds and any underexposure will exacerbate
digital noise. By taking the time to make these tests, you will
have the information needed to make the right choice for the
lighting conditions you are working under.
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Shutter speed vs. ISO speed
This is a balancing act based on achieving the best balance for
minimizing noise. Basic rule of thumb is that he always
shoots at the lowest possible ISO setting (in order to minimize
noise) depending on the working conditions.
If you have a tripod,
shoot at long shutter speeds to minimize noise because
digital capture is not subject to exposure or color-balance reciprocity
problems that plague traditional film capture.
Reciprocity refers to the inverse relationship between the intensity
and duration of light that determines the correct exposure
of film. During long exposures, fi lm responds much more slowly
than usual, and this affects both the color and the light sensitivity
of film. This is why color fi lm that is “pushed” in the photo lab
to higher ISO settings than what it was designed for sometimes
exhibits a color shift in a certain direction. The film’s light sensitive
grains must be hit by a certain number of light photons
within a certain time frame in order for the latent image to form.
Breakdown in the linear relationship between aperture and
shutter speed is known as reciprocity failure. Each different film
emulsion has a different response to long exposure. Some films
are susceptible to reciprocity failure and others less so. Some
films that are very light sensitive at normal illumination levels
and normal exposure times lose much of their sensitivity during
long exposure times, and some films that have low ISO ratings
Better available light photography/Focal press
