by Guy Lerner
November 30, 2003
A few months ago I came across an ingenious device that looks to solve the problem of inconsistent and inaccurate white balance and exposure in digital cameras: the Expo/Disc.
The color of color
Before I delve into a review, however, some backtracking is necessary to "set
the scene" - so to speak. Accurate exposure is possibly one of the hardest
photographic skills to master. Admittedly though, camera technology has advanced
to such a degree that today exposure is far less hit-and-miss than it was in the
past. Digital photography has narrowed the margin of error even further, with
most cameras able to show you a detailed preview of your photo seconds after it
was taken, allowing for fast and accurate adjustments to exposure on the spot.
But
digital photography brings with it its own set of challenges. For professional
photographers, one of those is white balance. The problem is simple
enough: photographers want to capture a scene as accurately as possible, and
that means getting the correct exposure and white balance (the color temperature
reflected off the main subject, measured in degrees Kelvin) so that the colors
in the final print match those in reality.
Most digital cameras allow you to set the white balance of a scene in
different ways, from basic (an automatic setting guesstimated by simple sensors
in the camera), to advanced (custom adjustments to the color temperature).
Unfortunately, even with professional SLR digital cameras, the automatic white
balance reading can be fooled by the type, amount and even direction of light
falling on a scene, and tampering with temperatures can be time consuming and
unintuitive.
A clever solution to the problem is basing the white balance setting on a
custom setting, normally a scene exposed at 18% grey. This solution is based on
the design of built-in camera meters that try balance the exposure of a scene to
“neutral” (without exposure adjustment, most camera meters will expose a pure
black or pure white scene as 18% grey, which is considered neutral). This is
done by capturing a neutral scene, typically a card printed at 18% grey, or a
neutral-toned scene (some types of vegetation for example photograph as
neutral), and using the resulting photo to set the custom white balance
in the camera. (This assumes, of course, your camera has this feature. If it
doesn’t, consider buying a new camera).
While this is clearly the best way of balancing colors in a controlled scene,
it’s not always easy to fill a frame with a grey card. In the field, it’s also
not always possible to get the light falling on the grey card equal to the light
falling on the subject.
Enter the Expo/Disc
Designed by the late George Wallace (a student of Ansel Adams and other
photography masters), the Expo/Disc was created to simulate a perfectly-balanced
grey card in almost any situation. The Expo/Disc looks like an oversized lens
filter, and it does in fact attach onto the front of the camera lens like a
filter (actually it pops onto the front of the lens more like a cap, but the
principle is the same). It consists of a white plastic lens enclosing a series
of “diffusion” filters that are stringently calibrated to allow no more or less
than 18% of the light reflecting off a scene to enter the lens. Attach the
Expo/Disc to your lens, point at the subject, and shoot. The result is a perfect
grey frame which can then be used to set the custom white balance for shooting
the subject.
What
if the light changes, or you switch subjects? Simply repeat the process. It’s
quick and incredibly effective. You can even use the Expo/Disc to check the
calibration of your camera meter. As a rule, an accurate meter will record
direct sunlight at f/16 and 1/125 at ISO 100 (also called the “Sunny 16” rule).
With the Expo/Disc attached, set your camera to ISO 100, point at the sun, and
check the meter reading. Anything less or more than the above exposure is how
much you should be adjusting your meter down or up for any scene (for example,
if the meter reads 1/250 at f/16, you should overexpose your shots by one f-stop
(because your meter is underexposing by one f-stop).
Without getting too technical, any photographer who understands the basics of
exposure will be right at home with the Expo/Disc with minimal practice. If
you’re on the learning curve, the Expo/Disc is a great tool to carry along with
you whenever you’re setting up a scene. As a reference tool, I’d go as far as to
say it’s invaluable, certainly incomparable.
More than practical
But how valid the Expo/Disc is for your photography is something only you can
answer. It will certainly help you nail your exposures and set the correct white
balance. But many photographers (myself included) don’t subscribe to the letter
of the law when it comes to setting creative exposure or white balance. Digital
photography in particular has introduced an era of experimentation that lends
itself to creative freedom with very few limits. Technology is so advanced that
getting the right exposure is as easy as reading a graph on the camera screen,
and more expensive digital SLRs are making white balance considerations
secondary.
Sometimes “accurate” white balance is also less desirable. For instance, late in the day, the sun can paint a scene in warm, rich colors that you’d hardly want the white balance setting to counter. These “color casts” are usually the first thing many photographers try to eliminate, either in-camera with filters on the PC. But I’ve found that in many cases, my photographs lose the emotive tone I wanted to capture when the cast (be it warm, cool or artificial) is removed. Of course, there are instances when accurate white balance is imperative, such as when recording the skin tones for a portrait or the subtle nuances in a lilywhite wedding dress. Weddings, in fact, are made for the Expo/Disc; I can’t imagine a digital wedding photographer without one.
A final consideration, but a critical one, is the raw file. Any
digital camera worth its price is able to record photos in a proprietary or
“raw” format, which is basically a dump of the information collected by the
imaging sensor before any processing is done to it. In other words, it’s the
light reading as the camera saw it, without any extrapolation made for, among
other things, white balance. Software that reads and “develops” raw files allows
the photographer to set the white balance of the scene using by selecting a
white/black or grey point, with all other color values falling in place around
the selection.
Using raw files is the preferred method for professional photographers, so
the Expo/Disc has limited value if you primarily shoot raw. However, by using an
accurate custom white balance reading from the Expo/Disc, processing raw files
can be sped up significantly, and speed is something the professional
post-processing photographer can never have enough of.
Get one, but...
Should you buy an Expo/Disc? If you’re new to photography or want to start
working from a point of technical accuracy, then without question. Beginners and
amateurs may find the price of the Expo/Disc prohibitive, but the return in
accuracy and speed more than compensates – especially if you’re not
shooting raw. Professionals could well be grateful for a quick and simple way of
finding the right white balance for a scene, and checking the accuracy of their
camera meters. Even raw users will find value in getting the white balance right
first time.
Personally I don’t leave home without the Expo/Disc in my bag. I don’t always
use it, but when I need to, I’m sure glad it’s there.
The Wallace Expo/Disc is available in various filter sizes from www.expodisc.com. It scores four out of five Go Inside Magazing Review Lights.
(four green, one red)
Copyright © 2003