Frank Lloyd Wright's Rudin House: standard black and white image on the left, infrared on the right
No digital camera makes it as easy as the Leica M8 to use infrared light to create surreal pictures that stand out in radiantly bright green leafs in extreme contrast of a dark sky, for example. As is known, the barrier filter of the sensor cover glass is very weak for design-related reasons. Therefore an additional blocking filter is always recommended for normal photography to avoid a magenta cast of skin tones or black textiles.
For infrared photography nothing more is necessary than an infrared filter like the B + W IR 093 Black Red 830 F PRO. All B + W filters are made from high quality optically ground and finely polished, plane-parallel and streak-free glass.
The filter blocks out all visible light, resulting in pure infrared photographs. Light transmission starts at a wavelength of 800 nm with just 1 percent and rises at 900 nm to 88 percent.
Since infrared filters have a very large exposure factor and therefore require long exposure times, it is always recommended to use a stable tripod. Automatic exposure control should not be used because the exposure meter is calibrated for visible light only. The optimum exposure values can best be determined through a series of tests. The distance settings require some practice as well. As a rule of thumb for infinity focus under IR conditions multiply the focal length by 300. For example, for a 50 mm lens that is 15 meters.
These filters are available in sizes E39, E46, E49, and E55.
For other articles on this blog please click on Blog Archive in the column to the right
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Please make payment via PayPal to GMP Photography
Are there any lenses which don't require refocusing with infrared?
ReplyDeleteYes, but very few. For instance, the Leica 180mm f/3.4 Apo Telyt-R is such a lens. It is corrected for not just the visible spectrum but for infrared also. It does not need to be refocused when used with infrared.
DeleteCould that lens be used on an M8?
DeleteYes, with an adapter that converts the Leica R mount to the M mount. However, since the M8 has no live view provision, the lens would have to be focused manually. since there is no focus shift, it is relatively easy to focus the lens manually by utilizing the depth of field scale. However, since infrared photography usually results in relatively long exposure times because of the IR filter, it might be advisable to shoot the 180mm Apo Telyt R wide open to gain as short an exposure time as possible. That is no problem with this lens because by design, it reaches optimum performance already at maximum aperture.
DeleteCan I use the depth of field scale for correct focus?
DeleteYes, as long as you compensate for the focus shift. With a 50mm lens, for instance, you would set the 15 meter mark opposite the aperture you are using on the depth of field scale instead of the infinity mark. The same aperture on the other end of the depth of field scale will then indicate your minimum focus distance.
DeleteWhat would happen if I use a filter with not as high a cut off as the B+W filter that you describe in the article?
ReplyDeleteYou would get less of the infrared effect because part of your exposure would be from the visible spectrum.
DeleteWould that be the case with a dark red filter?
DeleteYes
DeleteIs 15 meters the same as 45 feet?
ReplyDeleteNo, it's about 50 feet.
DeleteIsn't the 300 times the focal length just a ballpark figure and is there a more accurate way to focus my lenses with infrared?
ReplyDeleteYes, it is. Of course the most accurate means would be to find out the focus shift of your lenses. Another means to increase focusing accuracy is to use the depth of field scale with the next larger aperture. For instance, if you are shooting at f/8, apply the focus settings on the depth of field scale for f/5.6 or even f/4. That should make up for any focusing errors that otherwise might occur.
DeleteBut f/5.6 or f/4 have less depth of field than f/8. Wouldn't that increase any potential focus errors?
DeleteNo. Please keep in mind that with the above example, you are actually shooting at f/8. You only apply the f/5.6 or f/4 depth of field scales.
DeleteGot it! Thanks
DeleteI am confused. Why can't you use the rangefinder?
ReplyDeleteThink back a bit to physics class in high school. When light transmits through a prism, it is split up into the spectral colors with red on one side and blue on the other. The same thing happens when light transmits through a single lens element, like a magnifying glass. With other words, regardless how you focus that lens, some of the "rainbow" colors will focus in front and some in back of the focal point, which is always your sensor or your film. Lens designers have learned to eliminate that problem by using more than one glass element in our lenses. This allows the lenses to focus all the visible light such that there are no out of focus parts. This is relatively difficult to do for light of the visible spectrum, and therefore infrared (and ultra violet) usually are being ignored. Films generally are not sensitive to infrared light and digital sensors are made such that they don't record infrared either. Since the Leica M8 has a certain infrared sensitivity, we can take advantage of that and take photographs with infrared light. However, since most lenses are not corrected for infrared light, we are faced with the problem that infrared light comes into focus in back of the plane of focus of the visible spectrum and thus would render out of focus images and since the rangefinder of the Leica cameras is designed for the visible light of the spectrum, it would render infrared images to be out of focus. Therefore we need to compensate for that with the above described methods.
Delete