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Tuesday, June 8, 2010

One Lens To Shoot Anything

Big-range zooms (10x and more) aren’t just for travel anymore. With good sharpness and contrast across their focal lengths, today’s models are some of the most advanced optics on the market and they’re designed for digital.

Labels: Lenses
Designed For Digital

For years, camera and lens manufacturers designed lenses for 35mm cameras. When digital imaging developed, most 35mm SLR manufacturers produced digital SLRs by adapting their 35mm bodies. This offered a number of benefits, including cost savings, familiar bodies for current SLR users and a wide range of existing lenses. Digital sensors require light to strike them at a more direct angle than 35mm film so results weren’t always optimal when lenses designed for 35mm film were used for digital imaging.

The Four Thirds System was introduced in 2003 (in the Olympus E-1) to eliminate this problem. Instead of adapting existing 35mm SLR bodies to digital imaging, Olympus started from scratch and designed a DSLR to be digital from the outset. The sensor size, lens-mount diameter and lenses were all designed with digital imaging in mind. The lenses send light to the pixels at a more direct angle, enhancing performance.

Non-Four Thirds manufacturers soon introduced lenses designed specifically for their APS-C image sensors (which, at around 23.6x15.8mm, are considerably smaller than 36x24mm “full-frame” 35mm film and sensors, but larger than 17.3x13.0mm Four Thirds sensors). This improved performance and reduced lens size, since the lenses didn’t have to cover the 43.2mm image circle required by 35mm film (and full-frame image sensors). Note that the higher-end APS-C lenses provide excellent performance, while the low-priced “kit” lenses are aimed more at the budget-minded user.

Along with lenses designed specifically for the smaller image sensors, the film-camera companies and independent lens makers also have been upgrading their full-frame lenses by improving the antireflection coatings and internal light baffling (digital sensors are much “shinier” than film, and poorly coated lenses can cause reflections and flare to appear in digital images).

Note that lenses designed for APS-C sensors generally can’t be used on DSLRs with larger sensors—vignetting would result, and in some cases, the rear lens element would interfere with SLR mirror operation. However, when a Nikon DX lens is attached to a Nikon full-frame DSLR, the camera automatically switches to cropped DX mode (DX lenses shouldn’t be attached to 35mm Nikon film SLRs, however). Canon’s EF-S lenses can’t be mounted on larger-sensor Canon DSLRs, and Sony’s DT lenses can be mounted on Sony’s full-frame DSLRs, but vignetting will occur.

Testing Your Superzoom

Each superzoom has one or more “sweet spots,” combinations of focal length and aperture where it produces its best image quality. Each also has one or more “sour spots,” combinations of focal length and aperture where it doesn’t perform so well. So it’s a good idea to test your superzoom at each of its marked focal lengths and each of its apertures to find out where these spots are for your specific lens. See the article on testing lenses in this issue, “The Certainty Of Sharpness,” for details on how to do it. It’s nice to know what to expect with your lens, so you can work around sour spots and favor sweet spots when possible.


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