Better Available Light Digital Photography : How to Make the Most of Your Night and Low-light Shots

Digital noise 59

Shutter speed vs. ISO speed

This is a balancing act based on achieving the best balance for

minimizing noise. Joe’s 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 he has a tripod,

he’ll shoot at long shutter speeds to minimize noise because

digital capture is not subject to exposure or color-balance reci-

procity problems that plague traditional fi lm capture.

Reciprocity refers to the inverse relationship between the inten-

sity and duration of light that determines the correct exposure

of fi lm. During long exposures, fi lm responds much more slowly

than usual, and this affects both the color and the light sensitivity

of fi lm. 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 fi lm’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 fi lm

emulsion has a different response to long exposure. Some fi lms

are susceptible to reciprocity failure and others less so. Some

fi lms that are very light sensitive at normal illumination levels

and normal exposure times lose much of their sensitivity during

long exposure times, and some fi lms that have low ISO ratings

After 40 years of using another
brand (read about it in the fi rst
edition of this book), Barry
recently switched camera systems
to Canon. One of the main reasons
for the switch was Canon’s ability
to produce better-quality image
fi les at higher ISOs with less noise.
Nowadays, he confi dently sets the
camera ISO to 800 and higher
without worrying about image
quality. © 2007 Barry Staver.

example, if the chip’s base area is fi ve times the average, then

light-gathering and light-storage capacities also increase fi ve-

fold. In the extreme case of low-light photography and ISO

ratings of 800 or faster, high signal-to-noise ratios give full-

frame sensors a greater advantage.