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Tuesday, January 31, 2012

The New Breed Of DSLRs

Canon, Nikon, Sigma and Sony are pushing into new territory with their latest high-end camera models

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The D4 can use all current AF and AF-S Nikkor lenses and most old ones. If DX Nikkor lenses, which are designed specifically for DX/APS-C format, are used, the camera will automatically crop to DX format. Currently, the lens lineup comprises 71 (including manual-focus and DX lenses), from a 14mm ƒ/2.8 super-wide-angle and 16mm ƒ/2.8 fisheye to a 600mm ƒ/4 supertelephoto, including macro and tilt-shift lenses, plus 1.4x, 1.7x and 2x teleconverters.

Sigma SD1
Sigma's DSLRs have always been unique. Besides having a reputation for simplicity, the Sigma DSLRs exclusively use the Foveon X3 image sensor. Thephotosensitive "pixels" in image sensors detect how much light strikes them, but can't detect its color. To get color information, conventional sensors are covered with a grid of red, green and blue filters, so each pixel records light of one primary color. The other colors for each pixel are produced via sophisticated interpolation using data from neighboring pixels. This process (known as demosaicing) creates image artifacts, which are mitigated by placing a low-pass filter over the sensor. The Foveon sensor (Sigma bought Foveon in 2008) takes advantage of the fact that light penetrates silicon to different depths, depending on wavelength: short (blue) wavelengths penetrate the least, green wavelengths somewhat deeper and red wavelengths the deepest.

The Foveon sensor stacks three layers of pixels, the top layer recording (mostly) blue light, the middle layer, green, and the bottom layer, red. Thus, each pixel site records all three primary colors, so there's no need for a filter grid, demosaicing or a low-pass filter. As a result, Sigma maintains that the Foveon sensor delivers a resolution equivalent to that of a conventional sensor of a somewhat higher pixel count. Exactly how much more is subject to debate, but around 2x is a common figure. This would give the SD1's sensor a lines-per-image-height resolution roughly equal to that of a conventional 24- to 28-megapixel sensor. The Foveon sensor also delivers a unique color rendition. Sigma's TRUE II (Three-layer Responsive Ultimate Engine) image processor optimizes output from the X3 sensor.

Camera-wise, the SD1 is a solid, pro-oriented, magnesium-alloy body that's sealed against moisture and dust. It has a 3.0-inch, 460K-dot LCD monitor (but no live-view or video capabilities), and the eye-level SLR finder shows 98% of the actual image area. There's an 11-point AF system with twin cross-sensors (you can select any of the points manually, if desired), and a 77-segment evaluative metering system with center-weighted and spot capability, as well. The single card slot takes Type 1 CompactFlash cards (UDMA-compatible).

Twin control dials provide direct access to exposure modes (program, shutter-priority, aperture-priority and metered manual), drive modes and user-chosen custom settings—and you can even activate mirror prelock without going into LCD monitor menus. There's also a built-in flash, which is a rarity on a pro DSLR. The hot-shoe takes dedicated external flash units, and a PC connector attaches to studio flash systems. Maximum flash-sync shutter speed is 1⁄180 sec.

Sigma offers more than 40 lenses for the SD1, from a 4.5mm circular fisheye and 8-16mm superwide zoom to an 800mm supertelephoto, including macro lenses. With the SD1's 1.5x focal-length factor, this gives you access to focal lengths equivalent to 12-1200mm on a 35mm camera, not counting the circular and full-frame fisheyes. Teleconverters of 1.4x and 2x are available.


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