The ExpoDisc; A White Balance Tool

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
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