There has been much discussion recently of problems related to Infrared Contamination when photographing brightly sunlit scenes with Digital Cinema CMOS Sensor Cameras. Slower speed emulsions used to be the answer when shooting film in these situations, but with the fixed sensitivity of the digital sensor, (ASA 320 in the case of the RED One), it is necessary to add many stops of Neutral Density compensation.
Neutral Density filters effectively cut the exposure so we can remain in the sweet spot of the lens, maintaining maximum clarity, and avoiding excess depth of field. However, these “ND” filters do nothing to filter the undesirable effect of excess Infrared contamination, which can be seen in an overall lowering of image contrast, even making certain shades or textures of black, appear as brown.
I decided to set up the perfect storm for IR contamination, shooting in the middle of a sunny summer day in front of my Los Angeles area home. Schneider Optics graciously supplied one of their new True-Cut 750 IR Filters which have been developed specifically to deal with this situation. While this is a subtle problem that is only visible after adding 4 or more stops of neutral density, if you want vibrant tones and rich deep shades of black when using a CMOS sensor to capture strongly lit daylight scenes, you might want to consider using such a filter. I’ve prepared a .pdf with RED Camera frame grabs which offer a graphic side-by-side comparison both with and without this filter. You can download them here:
To the naked eye, the blacks in the car, equipment case, and my daughter Meghan’s blouse, looked about the same. However, the blouse almost looks brown in the frame without the aid of the filter, and overall everything is quite milky compared with the frame after the IR filter was added. The images were photographed with a RED One camera using Build 15 software, with an ND1.8 at F5.6. The 2K TIFF frames were created with RED Alert using identical output settings, which were then cropped for the purposes of the graphic. (Note: there was no exposure compensation for the later shot with the IR).