The ExpoDisc; A White Balance Tool
George Schaub, May, 2007
Today’s digital photographers have more ways to control color than you
can shake a stick at, with programmed White Balance (WB) options, custom color
temperature bracketing, and even color maps through which you can toggle to
attain any color bias you want, and that’s just in the camera. It’s
almost as if all the designers thought everyone needed a color temperature meter
and the filtration to control color cast, bias, and neutrality to the nth degree.
Add to that the controls in software—especially raw converters—and
you have controls to satisfy even the most color obsessed among us.
ExpoDisc, Front And Back |
|
 |
The front of the ExpoDisc is composed of a diffusion grid that will
turn most any light source into a diffusion light source. The back
is a flat, diffuse panel, much like a softbox. The collar does not
contain threads and is not intended to screw into a lens. Rather,
you place it entirely over the lens collar and make your Custom
WB readings. A handy lanyard is attached to the device, making it
easy to carry around and use. |
|
This is not meant to demean the impulse to control color for good balance
and pleasing rendition. But given that you are a reasonable sort who wants fairly
neutral color rendition (true to how your eye adapts to the light source) that
you can, of course, tweak later, you want to check out a handy device known
as an “ExpoDisc.”
Designed to work with D-SLRs (and I suspect other cameras) with a Custom WB
preset control, the ExpoDisc Pro Digital White Balance “filter”
is a round disc within a rigid collar that can be slipped over various lens
diameters. (Prices are in the neighborhood of $100, depending on lens filter
thread diameter.) Once the disc is laid over the lens all you need do is pick
“Custom” on your WB control, make the measuring exposure by pointing
at the light source and then shoot away in that light source safe in the knowledge
that you will have a neutral color rendition.
ExpoDisc Sees |
|
Using the ExpoDisc is quite similar to doing Custom WB using colored
sheets of paper, except here you bias (and neutralize) color balance
by aiming directly at the light source (except of course bright
sun). Here’s what the ExpoDisc “shows” the WB
setup in the camera (here with an incandescent light source). Seeing
this the WB will make a setting to neutralize the color bias (here,
add blue). |
|
It’s really quite simple, as I found out when using it with a Nikon
D40. On the D40 you get to WB via the menu only (many cameras have a WB button
right on the camera body). After choosing PRE (WB preset) I placed the ExpoDisc
over the lens and pressed the shutter release while aiming the camera at the
light source. This created a reference color bias for the image processor. I
then removed the ExpoDisc; the WB setting remained for all subsequent shots
under that light source. The folks from ExpoImaging stress that you should not
aim the lens at the sun when measuring WB presets outdoors; this is just common
sense but worthy of reiteration here. The best bet is to aim it slightly off
to the side of the sun.
Diffuse Light |
 |
|
These shots were made inside a greenhouse on a bright day. Light
is coming through a diffuse ceiling, the white painted glass panels
of the greenhouse. The first shot (top) was made with the AWB (auto)
setting on a Nikon D40. The ExpoDisc-aided white balance shows a
cleaner white and truer colors overall (above).
All Photos © 2006, George Schaub, All Rights Reserved |
|
|
