On Jun 22, 2019, at 10:31 AM, Robin Myers via colorsync-users <colorsync-users@lists.apple.com> wrote:
Perfect reflecting diffuser 100 Fluorilon FWS-99 2009 99.9 Spectralon SCS-99 99.7 Kodak Gray Card 1977 (3 specimen average) 95.0 ColorChecker Passport 2013-12 Neutral 9.5 52.2 ColorChecker Passport 2013-12 Neutral 5.0 95.2
Spectralon is great stuff, but damned expensive. Expect to pay as much for a Spectralon target as a Canon L series lens. There’re two homebrew-style options that are typically plenty “good enough” in photographic settings. The first, if you want 99%+ reflectance, as close to “pure white” as you’re going to get without spending lots of money: PFTE (Teflon) thread seal tape. Not very durable, and it’s got basically an eggshell surface that’s a bit more specular than ideal (Spectralon is close to ideally Lambertian)...but it’s dirt cheap and you can get it anywhere. Use a bit of creativity and you can figure out how to wrap several layers around a card to make a target. If it gets dirty or damaged or lost...no biggie; all you’ve invested is your time, so just make another. The second is a styrofoam coffee cup (or packing material, etc.) Its total reflectance is a lot less...in the 80% range. But it’s much more spectrally flat than the photographic tools (ColorChecker, gray card, etc.). Outdoors or in mixed lighting, its near-cylindrical shape lets you sample the illuminant from all angles, which can be creatively useful. And, with the right combination of lens and cup, you can fit the cup over the lens and get a near-ideal uniform sampling of all the light in the scene — much like those hundreds-of-dollars custom white balance tools that fit over the lenses do, but, again, with near-perfect spectral uniformity. (Put the cup over the lens, take a picture, and use it for your in-camera custom white balance. It’s probably pretty close to where you want to meter, too; experiment some and you could get that dialed in perfectly and consistently.) Coffee cups are pretty reliable spectrally; the more creative shapes you might find in a craft store (spheres, cubes, etc.) are more hit-or-miss. Visually compare with some thread seal tape (if you don’t have a spectrometer) if you’re unsure. Last note: read everything Iliah has on the Raw Photo Processor / RawDigger Web site and accompanying blog. You couldn’t ask for a better crash course on camera exposure, metering, development, etc., etc., etc. Cheers, b&