Friday, February 29, 2008

Lenses: Designed For Digital

Far from simple marketing hype, the term "designed for digital" encompasses the entirety of lens technologies unique to the demands of image sensors and their various sizes.
By Harlon Mitchell Published in Lenses
Lenses: Designed For Digital

Smaller-Format Lenses

Even though a majority of lens manufacturers make high-quality lenses that can be used with full-frame sensors, sub-full-frame or 35mm film, they saw definite advantages in making a new line of lenses for smaller sensors. Olympus decided to do this exclusively with the Four Thirds System, so the smaller sensor and the lenses were matched perfectly from the start. Panasonic and Leica have since adopted the Four Thirds System in their cameras as well.

Chuck Westfall, Director of Technical Marketing for Canon USA, says, "The benefit of a lens designed for sub-full-frame sensors is a combination of things. By making a lens that has a shorter back focus, the glass is sitting in closer to the focal plane than a regular lens. That helps us actually reduce the size, weight and cost of the lens substantially compared to a conventional lens. The other thing that becomes an issue is, because of a smaller sensor, you need a shorter focal length than you would for a regular SLR."

If you have a telephoto zoom, you may like the fact that it has seemingly become more powerful because of the magnification factor. For your standard lens, though, you'll probably want to invest in one of the alternative short focal-length lenses that will give you back the standard focal length to which you're accustomed.

Steve Heiner, Senior Technical Manager for Nikon, says, "In creating lenses exclusively for Nikon's DX format digital SLR cameras, decreasing the size of a lens to two-thirds of what's necessary for the FX (full-frame) format wasn't all that simple. There are many obstacles that have to be overcome, otherwise it would only make the size of conventional lenses smaller, but not improve aspects of lens performance such as sharpness or eliminating vignetting."

Many DX Nikkor lenses have focal lengths similar to many non-DX Nikkor lenses says Heiner, but they're designed to present a smaller image circle to the DX format sensor, thus solving the restrictions of more conventional lens designs. The goal was to achieve a good balance between miniaturization in size and overall improvement in performance.

Digitally Optimized

But even before these smaller-format lenses, as of December 2000, manufacturers began modifying their lenses to improve performance with D-SLRs, without affecting their performance with 35mm SLRs. Vuslat Tatar, Sigma's International Division Section Manager, says, "When D-SLR cameras were first introduced to the market, several problems were experienced because the image sensor surface causes 'specular reflection,' which causes more flare and ghosting compared to the film surface in film SLR cameras.

"The other serious problem was light falloff in the corners, due to the micro-lenses located on the image sensors, which can't sufficiently capture the light coming from an oblique angle, thus causing vignetting. Therefore, lenses used with D-SLR cameras require a special lens coating that increases overall light transmission and a special design that aims to channel light at a more vertical incident angle that minimizes such problems."

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