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(Page 1 of 2 pages for this article 1 2 >) Filed under: Cameras •Production •Tips • Tiffen Goes Into Production on T1 Far Red FilterIf you own an EX1, EX3 or F35 then this is the filter you’ve been waiting for
As you may have noticed from previous articles, I’ve done a lot of research on which cameras allow infrared or far red to contaminate dark fabrics and change their color. There hasn’t been a satisfactory solution for the Sony EX1, EX3 and F35 cameras—until now.
Silicon is sensitive to infrared energy above all else, so camera manufacturers work hard to prevent their sensors from seeing anything but the visible spectrum. These three cameras don’t have a classic infrared contamination problem where they mistake heat energy, beyond the visible wavelengths of light, for actual visible light. Sony installs very effective hot mirrors in their cameras to prevent any IR from reaching the sensor(s), but as these cameras see what Sony calls “broad spectrum color” they tend to be very sensitive to red. This isn’t a bug, it’s a feature! This sensitivity to red can cause problems with dark fabrics that reflect not only infrared (which is cut very effectively in these cameras) but far red, which is red on the edge of the visible spectrum. Humans may have a little trouble seeing this hue of red but these cameras don’t, and sometimes it can be a bit much. The color red has, until recently, been the bastard stepchild of colorimetry because it’s very hard to reproduce properly—and thanks to Sony’s new broad spectrum color you’ll see beautiful hues of red you’ve never seen before. But there’s always a price to pay. A while back I tested a prototype filter for Tiffen that worked brilliantly. It cut through far red like a knife. Previously the only filter that worked on any of these cameras was the Schneider Tru-Cut 680, which worked exceptionally well except for vignetting on wide lenses: the dichroic hot mirror was so thick that when viewed at an angle the filter turned cyan, so wide lenses yielded an image that was cyan around the edges. Tiffen’s filter, originally known as T1 for “Test 1,” used dyes alone to absorb far red, completely avoiding the risk of vignetting. Their reasoning was this: if the camera’s hot mirror works fine, and since we’re cutting visible light instead of heat energy, it’s clear that we can use a dye, which doesn’t vignette, over a hot mirror, which will. (The more a hot mirror cuts, the heavier the dichroic coating has to be. When cutting non-visible infrared the dichroic layer can be fairly light, but cutting visible far red requires a very heavy dichroic coating, which causes off-axis vignetting on wide lenses.) While the T1 prototype worked marvelously, Tiffen wasn’t satisfied. The dyes used in the prototype weren’t stable and would fade over time. After trying a number of different formulas, all of which I’ve tested at one point or another, they settled on the current version which works exactly the way the original T1 did but without the original’s color instability. Having perfected it, Tiffen is now ready to release this filter into the wild. If you want to see how it does, travel with me to page two and cast your gaze upon my homemade far red/infrared test chart…
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