Field Test: Expodisc

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The disc is thick, feels very solid in your hands and is available in 58mm, 62mm, 67mm, 72mm, 77mm and 82mm filter sizes. On one side, you'll notice a micro prism-like pattern that gathers light from a 180 degree angle of view. When flipped over, you see a smooth, opaque white acrylic, similar in color and feel to white Plexiglas. The two circular discs are enveloped by a black, high-grade aluminum that has a perfect finish and texture. You'll also notice a string that attaches from the aluminum filter casing to the supplied neck strap. I found this combination to be smartly designed and convenient for me when I was shooting in scenes that had changing light conditions. I tend to wear shirts with pockets on them, so rather than allow the filter to dangle from my neck, it was easy to put the disc in my pocket and the strap around my neck, keeping it ready at a moment's notice. If having the disc in your pocket isn't your cup of tea, ExpoDisc also provides a well made holder that has a loop in the back for belts. My only complaint with the holder is that it's got a velvet lining. While this looks and feels great, the disc fits into the holder very tightly and rubs off the velvet, which attaches onto the ExpoDisc. I had to consistently wipe down the disc after storing the filter in the case because there was enough of this black residue on the disc that I felt it could have the potential of throwing off the color reading when I white balanced. Still, this is a minor inconvenience and I expect that the more I use the case, the less this will be an issue. If I were grading the build materials, the ExpoDisc would receive a solid "A."

I noticed three small golden stubs on the aluminum section of the filter, and after close inspection, realized that these are three very small spring-loaded balls which are used to hold the filter in place on a lens. This to me is groundbreaking in filter design and after I realized what they did, I found it very convenient to use. No screwing this filter on and off; the ExpoDisc simply pops into place and holds firm. Of course, this is assuming that you have the proper filter diameter for the lens in use. Not all of my lenses use the 82mm filter size though, but it was almost just as easy to hold the ExpoDisc in front of my lens and make my white balance readings. I also own a 14mm Nikkor lens that was too wide to use with the ExpoDisc. It showed uneven lighting through the viewfinder, and I think that wouldn't make an accurate measurement. To avoid this situation, I simply used another wide angle lens with a smaller diameter to make the light balance reading and then changed lenses. It's not a huge issue, but it would be nice to have a disc large enough to cover these types of lenses -- particularly since most lens makers now have ultra-wide angle lenses and super telephotos with large diameters for their digital cameras.

According to ExpoDisc's CD manual, the recommended procedure is to use a custom white balance -- this means that using an autoexposure mode (A, P or S) or a Manual Exposure (M) and then exposing the sensor to a pure white light. With a Nikon D200, which is the camera we used for the images in this story, you depress the WB button on the top left portion of the camera body and change the setting to "Pre" in the LCD. Once the "Pre" is flashing, point the camera, lens and disc toward your light source and depress the shutter. If the camera records a good white balance, you'll see a "Good" flashing on the LCD. No frame is actually recorded by doing this, so the best backup is to make an image with the Expodisc in place and use a RAW file format, which will not only allow you to convert several images at once, but save those conversion settings for future use. In the case of studio images, you need to determine a correct exposure first, then point camera, lens and Expodisc toward the strobe from the subject location and balance.

Every camera manufacturer has a slightly different method for setting a custom white balance, so be sure to consult your user's manual for brand and model-specific directions for setting a custom WB.

(If you're not able to use a custom white balance, simply shoot a properly exposed frame with the filter in place, then in Photoshop or other image editing program, pick any point on the image as a middle gray in Levels and process all like-lighted images with the same settings.)

Overall, I found the ExpoDisc to be one nifty little slice of imaging technology. I shot one commercial job, at a car show with lighting that was a mixture of strobe, Sodium and Mercury Vapor. The paint on the cars looks wonderful -- no green casts and absolutely no post-processing for color correction. I'm guessing that on the first job, this filter saved me an hour or two of Photoshop work. With that kind of time savings, I can easily justify its cost. I also found out that I tend to like warmer coloring in my images. I was a little surprised at the coloring when I first used the disc, and had to keep reminding myself that this disc is designed to produce neutral colors, which it does very, very well. I tend to think though that most photographers will gravitate toward the warmer toned ExpoDisc because of the warmth in skin tones and landscapes. And the design is just flat-out clever. I am amazed at the simplicity, yet high precision of this small device. George Wallace would be proud of his family for their continued pursuit of his dream. It's a welcome addition to my camera bag and I highly recommend it.

In the Box:
1 Expodisc (available in 58mm, 62mm, 67mm, 72mm, 77mm and 82mm filter sizes)
1 Neck Strap
1 Quick Start Guide
1 Instruction CD
Belt-loop carrying case

Specs:
Within 1% color accuracy

Website: www.expodisc.com

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