The drawback? Conventional digital cameras use Bayer-filtered sensors. The photodiodes (“pixels”) in image sensors can’t detect color; they detect how much light strikes them, but not what the wavelengths are. To obtain color information, most digital cameras use a grid of red, green and blue filters known as a Bayer array (named for the Kodak scientist who came up with the concept) over the sensor, so that each pixel receives light of only one of these primary colors. The missing colors for each pixel are then derived by interpolation, using data from neighboring pixels and complex proprietary algorithms in a process known as demosaicing.
Sigma’s digital cameras—the SD1 Merrill DSLR, the DP1, DP2, DP3 Merrill and the DP2 Quattro compacts—use a unique Foveon sensor, which doesn’t employ the Bayer filter grid used by most other sensors. Instead, the Foveon sensor takes advantage of the fact that light penetrates silicon to different depths, depending on wavelength: short (blue) wavelengths penetrate a little; medium (green) wavelengths, deeper; and long (red) wavelengths, still deeper. The Foveon sensor stacks three layers of pixels, the top layer recording mostly blue, the middle layer mostly green and the bottom layer mostly red light. It’s more complicated than that, but this simplified explanation makes the point: Unlike Bayer sensors, Foveon sensors record all three primary colors of light at every pixel site, so there’s no need for the array, demosaicing or an anti-aliasing filter. The result: better resolution than a Bayer sensor of similar horizontal-by-vertical pixel count provides. A side benefit is that monochrome images are sharper than those from a Bayer sensor of equal pixel count. And unlike the monochrome digital cameras, the Sigma bodies with Foveon sensors provide three color channels, allowing you to adjust each individually for optimum control over the final monochrome image. The drawbacks? There’s some light loss (i.e., high ISO performance isn’t as good as with monochrome cameras), and the Foveon sensors are all APS-C—smaller than the sensors in the monochrome cameras.
This system works well. Every Canon, Nikon, Pentax and Sony DSLR uses it, as do all medium-format cameras except the Phase One IQ260 Achromatic discussed in this article—pro-quality color images, for sure. (Sigma’s digital cameras with their Foveon sensors use a different approach; see the sidebar.) The problem is that each pixel receives light of just one primary color, which cuts down on resolution (because a portion of the data at each pixel is interpolated) and sensitivity (because the filters absorb some of the light that would reach each pixel otherwise). And the demosaicing process creates moiré and exacerbates aliasing that occurs when a pattern in the subject or scene conflicts with the pixel grid of the sensor. If you convert one of these images to monochrome, you still have the problems of reduced resolution and sensitivity, as well as aliasing.
To reduce the moiré and aliasing problems, most sensors have an anti-aliasing (AA) filter, or optical low-pass (OLPF) filter, which reduces those problems by slightly blurring the image at the sub-pixel level. Obviously, this further reduces resolution.
For the monochrome specialist, there are a few dedicated monochrome digital cameras. These omit the Bayer filter grid, since color data isn’t needed, just luminance (brightness) data, and therefore eliminate demosaicing and its problems. So every pixel receives all the light possible, improving sensitivity, and every pixel provides luminance data—there’s no demosaicing process, further improving resolution. And since there’s no demosaicing, there’s no need for the resolution-reducing AA filter—further enhancing sharpness. These monochrome cameras provide increased pixel-level sharpness, enhanced contrast, smoother tonal transitions and increased sensitivity (higher ISOs). Their primary drawbacks are cost (they start at $7,950) and the fact that you can’t shoot normal color images with them. You also lose the ability to adjust each color channel independently, as you can with color digital images—there’s just one channel. So you have to use color filters over the lens to produce black-and-white film-style tonal adjustments. (In black-and-white, a color filter lightens objects in a scene of similar color and darkens objects of complementary color, hence yellow and red filters are used to darken blue skies and make white cloud formations stand out dramatically, and green and yellow filters are used to brighten foliage, etc.)
|Black-and-white infrared film records images by infrared radiation alone, or by visible light and infrared, depending on which filter you use over the lens. A popular effect is with a deep red filter—white clouds and healthy green foliage stand out dramatically against black skies.
The sensors in most DSLRs have a filter that blocks infrared radiation to keep it from unduly influencing the images, so you can’t readily do infrared photography with these cameras. With Sigma DSLRs, you can easily remove the infrared-blocking filter, allowing infrared photography. There are companies that will remove the IR filter from your camera’s sensor (which voids the camera warranty, incidentally) to permit infrared photography. The Phase One IQ260 Achromatic doesn’t have the IR-blocking filter, so you can do infrared photography with it as-is (using the appropriate red IR filter over the lens). You also can rent infrared-modified DSLRs.
Note that lenses don’t focus infrared at the same plane as visible light, so you must focus manually and adjust for the difference.
There’s a small, some may say elite, group of dedicated monochrome cameras. These aren’t models with gimmicky firmware changes or cosmetic additions. These are true monochrome-dedicated cameras that have been built from the ground up to shoot the very best black-and-white images possible. If that’s what you need, this elite group is where you want to look.
Leica M Monochrom
Leica has been producing its splendid M-series 35mm rangefinder cameras since 1954 and digital versions since 2006. Among the current digital models is the first 35mm full-frame monochrome digital camera, the M Monochrom, introduced in 2012. It features an 18-megapixel CCD sensor that was designed specifically for monochrome digital imaging with legendary Leica M-series lenses. The 35.8×23.9mm sensor delivers 14-bit uncompressed or losslessly compressed RAW (DNG) files measuring 5212×3468 pixels or lightly compressed JPEGs measuring 5216×3472 pixels. A special layout of microlenses atop the sensor helps produce uniform exposure and excellent sharpness from corner to corner. A special glass sensor cover blocks infrared radiation above 700nm.
Because there’s no demosaicing, the M Monochrom can provide a histogram of the RAW data. This is very useful, and much better than conventional Bayer-sensor cameras, which can only display histograms for camera-created JPEG images from the RAW data because it shows actual clipping points, not JPEG clipping points. The camera also allows you to apply toning effects to JPEG images in-camera. Camera-wise, the M Monochrom is an M-series Leica, ruggedly and precisely constructed of magnesium alloy with brass top plates and baseplates. Focusing is manual, via Leica’s long-proven M-series rangefinder system. The camera can use all M-series lenses, which range from 16mm to 135mm. There’s a 2.5-inch, 230K-dot LCD monitor for reviewing images and camera-setting menus (but no Live View), and a microprocessor-controlled, vertical-travel focal-plane shutter with speeds from 32 to 1⁄4000 sec. (plus B, for exposures up to 240 seconds) and flash sync up to 1⁄180 sec. Maximum frame rate is 2 fps. Images can be saved on SD or SDHC (but not SDXC) cards. Dimensions are 5.5×3.1×1.5 inches; weight is 21.1 ounces (with battery). Estimated Street Price: $7,950. Contact: Leica, us.leica-camera.com.
Phase One IQ260 Achromatic
Phase One’s IQ260 Achromatic is a medium-format digital back with a huge 53.7×40.3mm, 60-megapixel (8964×6716-pixel) CCD sensor designed for black-and-white photography. Not only is there no RGB Bayer filter grid or AA filter on the sensor, there’s no IR cutoff filter, either, so the camera can be used for infrared and ultraviolet, as well as visible-light photography. The IQ260 Achromatic captures 16-bit IIQ losslessly compressed RAW monochromatic black-and-white files and outputs TIFF-RGB, TIFF-CMYK and JPEG. ISO range is 200-3200 (vs. 50-800 for the Bayer-array IQ260 in full-res mode), a two-stop improvement. Dynamic range is 13 stops. Maximum capture rate is 1 fps.
There’s a 3.2-inch, 1150K-dot touch-screen LCD monitor with Live View. You can save images to a memory card or shoot tethered to a computer via USB 3 or FireWire. You can connect the camera wirelessly to your iPad or iPhone via Capture Pilot for added operational functionality.
The back is made of aircraft-grade aluminum and sealed against the elements. It can be used on a wide range of medium-format and technical cameras, including the Phase One 645DF+, Mamiya 645DF+, Hasselblad H1, H2 and H4, Contax 645AF, and via FlexAdapter, 4×5-inch Arca-Swiss, Cambo Linhof, Toyo, Sinar, Plaubel and Horseman. Estimated Street Price: $45,000. Contact: Phase One, phaseone.com.
RED EPIC Monochrome
Maker of high-end pro DSMC (Digital Still & Motion Camera) models, RED offers monochrome versions of its EPIC camera. The EPIC-M DRAGON Monochrome ($31,500, body only) features a 6K (6144×3160-pixel) DRAGON monochrome sensor, and the EPIC-M Monochrome ($25,000, body only) and EPIC-X Monochrome ($20,000, body only) feature a 5K (5120×2700-pixel) Mysterium-X monochrome sensor. These are great devices for shooting professional black-and-white video, but they also deliver excellent still frames—6K is 6144×3160 pixels, or 19.4 megapixels (the DRAGON can record 6K at up to 100 fps); 5K is 5120×2700 pixels, or 13.8 megapixels (the EPIC-M and EPIC-X Monochrome can record 5K at up to 120 fps).
Dynamic range is 16.5 stops; for the others, it’s 13.5 stops. Focusing is manual, and mounts are available for Canon, Nikon, Leica and PL lenses. Contact: RED, www.red.com.