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Tuesday, March 1, 2005

Gadget Bag: New Lenses In A Digital Age


The latest designs bring true wide-angle capability and more to the digital format


The Sigma 18-125mm ƒ/3.5-5.6 DC offers an impressive focal length range running from moderate wide-angle all the way out to a strong telephoto. Along with Sigma's own line of digital SLRs, the lens comes in mounts for Canon, Nikon, Minolta, Olympus 4/3 and Pentax small-format D-SLRs. The equivalent focal lengths vary according to the magnification factor of the camera on which it's mounted—with Sigma's 1.7x cameras, it's approximately 30-212mm.

The Tamron SP AF11-18mm ƒ/4.5-5.6 Di-II LD Aspherical (IF) (available in Spring 2005) fits Nikon, Canon and Konica Minolta D-SLRs. It features an angle of view equivalent to a 17mm or 18mm lens on the wider end, depending on the size of the camera's image sensor, and zooming out to an equivalent of 27mm to 29mm.

The Tokina AT-X 124 AF PRO DX zoom fits Nikon and Canon small-format D-SLRs, providing a 12-24mm focal length range equivalent to 19-38mm for Canons and 18-36mm for Nikons. The lens has a constant ƒ/4 maximum aperture at all focal lengths.

The Pentax smc P-DA 14mm ƒ/2.8 ED (IF) gives *ist D and *ist Ds shooters the fast, wide equivalent of a 21mm ƒ/2.8 lens. Like other lenses with internal focusing, its front elements don't rotate—a real boon for users of graduated neutral-density filters and other position-dependent accessories.

Resources
Canon
(800) OK-CANON
www.usa.canon.com

Nikon

(800) NIKON-UX
www.nikonusa.com

Olympus
(888) 553-4448
www.olympusamerica.com

Pentax
(800) 877-0155
www.pentaximaging.com

Sigma
(800) 896-6858
www.sigma-photo.com

Tamron
(800) 827-8880
www.tamron.com

Tokina (THK Photo)
(800) 421-1141
www.thkphoto.c

Anti-Reflection Technologies
Another difference between film and digital is the relatively mirror-like surface of image sensors. In some cases, the sensors' smooth face can reflect light back through the rear lens elements, where the beams bounce around until re-exiting the rear glass and striking the imager as flare or a ghost image. The series of ƒ/2.8-speed, L-series zooms, such as its CanonEF 70-200mm ƒ/2.8L IS USM, have optimized lens element shapes and anti-reflection coatings to minimize or eliminate these ghosts. Unlike the special small-format digital lenses, this lens series is a part of the regular 35mm lineup and provides outstanding image quality on both film and digital cameras. The Tamron Di and Di-II-series lenses, such as its SP AF17-35mm ƒ/2.8-4 Di LD Aspherical (IF), feature improved multi-coating and interior light baffling to combat off-the-sensor reflections. The lenses offer improved resolution, contrast and freedom from flare with film SLRs as well. This also is true of Sigma's new Super Multi Layer Coatings now used on allSigma lenses.

Canon and Nikon also have taken care to subtly curve the protective front filters on their super-telephoto lenses. The filters' new meniscus shape disperses the reflections from the image sensor that would otherwise bounce off the rear of the filter and straight back onto the sensor's face. The curved filters now are standard on all Canon fast IS super-telephotos, like its EF 500mm ƒ/4L IS USM; Nikon has introduced a curved filter on its 300mm ƒ/2.8G ED-IF AF-S VR Nikkor.

Other Technologies
Digital photography still is photography, so other new lens technologies, not strictly for digital, are critical. Chief among them are the lenses that shift a group of their optical elements to compensate for camera shake. These lenses enable handheld photography at shutter speeds two to three stops slower than you'd use with a conventional lens of the same focal length. Look for Image Stabilizer (IS) lenses from Canon, like its EF 28-135mm ƒ/3.5-5.6 IS USM; Vibration Reduction (VR) lenses from Nikon, such as its 24-120mm ƒ/3.5-5.6G ED-IF AF-S VR Zoom-Nikkor; and Optical Stabilizer (OS) lenses from Sigma, like its 80-400mm ƒ/4.5-5.6 EX OS APO.

Another new technology, Diffractive Optics (DO), relies on applied physics, using a vastly different means to bend light rays than the curving glass elements we're used to. A special element within a DO lens directs light waves through a finely etched concentric lattice to achieve focus. By varying the lattice's spacing, the DO element can provide the advantages of an aspherical lens element and help control chromatic aberrations, too. Lenses with Diffractive Optics technology, such as the Canon EF 70-300mm ƒ/4.5-5.6 DO IS USM, boast improved image quality and can be made about one-third smaller than conventional lenses.

Nikon's Phase Fresnel lenses are similar, providing the same image quality and size advantages as Diffractive Optics. The Nikon TC-E3PF 3x telephoto converter lens brings this technology to its Coolpix 8400 advanced compact.


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