IMAGE IS EVERYTHING PHOTOS COURTESY OF BOSCH SECURITY
A camera with an IR-corrected lens (left) maintains its focus in the dark, while a camera without an IR-corrected lens (right) experiences a focus shift.
they express in terms of line pairs. Unfortunately, that number refers to the performance of the lens “at the dead center” and may not represent its per- formance at the edges. “You could have a severe drop-off in image qual- ity at the edges,” she says. “You can’t believe all the claims out there, but unfortunately, it becomes a matter of buying and trying different lenses.” Iniguez adds that this only serves to underscore
the fact that there are no overriding standards for measuring and reporting lens quality. “There’s not a standard definition among manufacturers or within the industry about the true definition of what, say, a 5-megapixel or 3-megapixel camera really is,” she says.
DAY/NIGHT
In addition to megapixel lenses, day/night lenses are also gaining traction in the industry, Wolk says. The main issue around these lenses is ensuring that
What’s Old Is New Again
Combating image distortion doesn’t necessarily require the “latest and greatest” technologies, says Glenn Wolk of Tekstar Optical. Instead, you can “trade down” lenses by formatting a larger-format lens for a smaller-format camera. For example, he says, using a 1/2-inch lens on a 1/3-inch camera produces results that may be surprising to some.
“By hitting the center portion of the larger lens with the smaller chip, it allows the camera to hit the sweet spot of the lens,” he says. “With a megapixel camera, you’d be amazed at the quality of the picture.” Beyond being a more-than-adequate solution to the problem of dis- tortion, he says, using older, larger-format lenses is both cost-effective and timeless.
“When people are swapping out older cameras, I always tell them, ‘Don’t throw out the lenses. Clean them up and they’ll be absolutely amazing on a smaller camera,’” Wolk says. “Toss the camera but keep the glass; its shelf life is indefinite.”
84 November 2010
they have the proper infrared (IR) coating to reduce the focal shift between day and night. Day/night cameras are designed to “see” both visible light and IR light, both of which are present in most light sources. Without the proper IR coat- ing, the red, green and blue color filters that light passes through also allow IR light to pass through, creating an image that is clear at night but blurry during the day, Wolk says. “If you’re only looking 20 feet or so away, it’s not that big of a deal,” he claims. “But the farther out the view is, the more drastic the focus shift you’ll notice.” According to Peterson, a “true” day/night cam- era physically switches its IR filter out of the lens’ light path, enabling the camera to see IR light, whether naturally occurring or artificial. And because street lights, the sun, the moon, and other visible light sources include IR light, a day/night camera can easily capture and record its field of vision. The day/night lenses required by these cam- eras to maintain proper focus in all light are more complex and therefore more expensive. So when it comes to day/night, Peterson says that before investing in a more expensive IR camera and lens, installers should ask themselves whether their customer actually needs a day/night setup. The answer, he believes, is “not necessarily.” While a day/night camera has to be able to trans- mit IR light through the lens, day-only lenses have an immovable IR filter. Most security cameras, Peterson says, are designed for day-only use, so by keeping out the IR light, the IR filter improves an image’s color quality and sharpness. With this in mind, IR illumination could also
be used to augment that visible light found in the camera’s field of view. IR LEDs mounted to shine on the object or area the camera is covering can make it overkill to use a day/night camera and lens.
IF ALL ELSE FAILS… Considering the wide variety of lenses that are available, coupled with the lack of standards for measuring and reporting specs, Wolk says the best method for finding the right lens for the right situ- ation is an old-fashioned one. “I always tell people to try out lenses,” he says.
“All the numbers and specs in the world are no sub- stitute for a real-world, side-by-side comparison. Testing various lenses under the same conditions is still the best way to make a decision.” ■
www.sdmmag.com
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