Thanksgiving week, while placing an order for a big box of letter size paper for digital proofs, I broke down and forked over the $110 for a 72mm ExpoDisc. This device was developed more than a decade ago by a fellow named Wallace who thought that what every small format photographer desperately needed was a tool to convert his 35mm SLR into an incident light meter. Why, I was never clear about, though he did send me one in 52mm to try on my Nikons, hoping for a write-up in Photo Techniques. I found that the interesting design, with a white Plexiglass plate facing the lens and a honeycomb of lenses facing the world, did indeed give incident readings that matched a good hand-held meter. They even were, as advertised, identical to readings with a ping pong ball style receptor, not a flat white receptor, thanks to the honey comb material. In a fit of what struck me as precision-without-purpose, the vendor was adamant about how the device was perfectly color neutral--they even enclosed with each unit an individual test report showing how close its transmission was to 18% for density, and also how extremely close to neutral it was in color. That sample I received, and the one I just bought more than ten years later, both have tests that are several decimal points off perfection, in a context where 1/6th of a stop is several times farther away from the norm. Since in-camera meters are notoriously not so hot at color perception, I didn’t see the point of the perfectly neutral color for a device meant to convert a Nikon F3 into an incident light meter.
Enter digital capture. The biggest problem with shooting jpg files in-camera (the issue of RAW vs. JPEG I will set aside for another time) is that if you seriously miss your white balance, there isn’t enough margin to get back to correct color since you are dealing with an 8-bit file that has already been compressed once. Suddenly that excessive attention to color neutrality, which I still say made no practical sense at the time, makes the ExpoDisc a perfect tool--now--for shooting digital captures in JPEG mode.
Shooting in JPEG, you’ve got to get the exposure right, which should be simple for anyone who grew up shooting chromes, though a bit more challenging for photographers whose brains have become hard-wired for negatives. However, you’ve also got to get the white balance right. This is much more difficult. Auto white balance varies from really good to really awful on various high-end digital cameras, but even the really good ones aren’t reliable enough at it. You can do a custom white balance by setting off a WB button instead of the shutter button while aiming at a white (or gray, depending on the camera) card. But that’s incredibly ridiculous procedure. Unless you always work with long lenses, even a card a foot across isn’t big enough to fill the frame. Where do you carry it? Even if you have a pocket for it, you must be sure to wear neutral gray clothing or the light reflecting from your clothes will ruin the color balance.
It was snowing in western Connecticut Thanksgiving Day morning, so I went out to see if I could find this year’s Christmas card. In the past, snowstorm conditions have proven to be a monster for digital capture white balance. Shooting RAW last winter, I found I had to fiddle with the white balance of every snow shot in post processing because the Auto setting leaped about like a ping pong ball, and neither 5300 nor 6000 degree Kelvin manual WB settings looked right. So I used the disc to set custom WB for each scene and my snow was neutral to within 2-3 points out of 255 across the three channels every time. In the week gone by since, I’ve been out on several walkabout shoots and made several hundred captures with my Olympus E-1 using the disc. Each time the light changes or I turn a corner from sun to shade, I snap a new white balance so the camera is ready if a subject turns up. Result? Prettiest color you ever saw.
So, a silly, nobody-needs-it-in-the-first-place, over-engineered product has been transformed into a valuable, perhaps indispensable, tool. You never know.
Posted by CARL WEESE