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Filed under: Cameras •Production •Tips •Training •

EX1/EX3 IR Filter Shoot-Out

FOURTH UP: TIFFEN’S IR ND FILTERS

Here’s the setup I tossed together to test the Tiffen IR ND filters. I apologize for the text overlay on the EX1 image: I was recording HD-SDI out of the camera and was in too much of a hurry to turn all of that off. (I was prepping for a Porsche spec spot, to be written up in the very near future.)

These first shots are through a Schneider ND .9 filter:

You can see heavy red contamination in the DSC chart bag on the right side of frame. Now let’s try the Tiffen IR ND (non-Hot Mirror) filter:

And there’s the proof. This camera has the same problem the Sony F35 does: the chip has a Hot Mirror filter on it that starts cutting at 700nm and rolls off somewhere between 720nm and 750nm, which is why the Schneider Tru-Cut 680 works and the Tru-Cut 720 and 750 don’t. The Tru-Cut 680 cuts low enough that it eliminates any far red that sneaks through heavy ND filtration, because 680nm is the limit above which ND filters start passing light, but the dichroic coating that allows for such a low cut is too heavy to use with wide lenses as it causes cyan vignetting. The Tiffen IR ND filter appears to use a yellow-greenish dye that cuts the complement of far red, and since the cameras already have a very effective Hot Mirror built in there’s no need to use an additional Hot Mirror in front of the lens.

That makes the Tiffen IR ND filters the best choice for two reasons: the lack of a Hot Mirror means no worries about color vignetting on wide lenses, and the fact that there’s no dichroic Hot Mirror coating reduces the cost by about US$400 per filter. It’s also important to note:

These filters CAN NOT be used with conventional ND filters. The yellow-green dye that makes these filters work is proportional to the amount of ND in the filter, so an ND 1.2 filter will have much more yellow-green dye in it than an ND .3.

For example, a Tiffen IR ND .9 combined with a conventional ND .6 will still let through ND .6-worth of far red light. The proper solution would be to use a Tiffen IR ND 1.5.

That the EX1, EX3 and F35 have more than a little in common probably shouldn’t be a surprise considering that they all come out of the Cine Alta group at Sony. They appear to be using similar broad spectrum dyes on the sensors of both cameras, the result of which seems to be an increased sensitivity to far red at the edge of the visible spectrum. As you’ve read in my previous articles, silicon is most sensitive to wavelengths in the infrared range—and the fact that it is also sensitive to visible light wavelengths is pure gravy. The Hot Mirror filters on the sensors actually cut most of the light that silicon is sensitive to (silicon is most sensitive to light in the 1000-1100nm infrared range) in order to make it usable in the narrow band of visible light (380nm-750nm) that we can see. It only makes sense that these sensors should be more sensitive to red, because red is the closest component of the visible spectrum to the range where silicon is most sensitive.


The blue channel, on the other hand, is at the other end of the visible spectrum and has the least impact on silicon. That’s the reason the blue channel is always the noisiest: the weak signal from the blue photosites has to be “pushed’ to bring it into line with the red and green signals.

Thanks once again to camera assistant Rod Williams and to Chater Camera for their help in performing these tests. Any errors, if they exist, are solely my responsibility.

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Excellent test! Would the Tiffen IRND have to be the first filter light hits, or could it be used as a screw-in filter on the lens behind a matte box?

Posted by DR  on  02/26  at  10:20 AM

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It doesn’t have a reflective Hot Mirror so I don’t see a need for it to be the first filter in the matte box.

Posted by Art Adams  on  02/26  at  05:11 PM

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Test

Posted by Art Adams  on  03/05  at  04:20 PM

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where does one find a Schneider Tru-Cut 680?  i’ve looked everywhere.

thanks.

Posted by .(JavaScript must be enabled to view this email address)  on  03/14  at  12:02 PM

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I don’t know that they are commercially available. I got one to test when Schneider first brought IR filters on the market but I think the only one they’ve officially released is the Tru-Cut 750, which works great on the RED.

You should give them a call. They’re about the nicest people you’d ever hope to do business with.

Posted by Art Adams  on  03/14  at  12:23 PM

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Thanks Art.  yeah,i’ve gotta EX1.  i second that about Scheider.  I see many of their reps through the year.  very nice people.  i’ll call them monday.

Posted by .(JavaScript must be enabled to view this email address)  on  03/14  at  12:52 PM

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