IMAGE IS EVERYTHING PHOTO COURTESY OF THEIA TECHNOLOGIES
Looking at two images produced using two different wide-angle lenses on the same camera in the same setting, the difference between a recti- linear lens (left) and a fisheye lens (right) is observable.
tion. “Often a wide-angle straight lens is rounded out because of the distortion of the lens,” he says. Until recently, the only option for a wide-angle camera was a fisheye lens. So these lenses were used almost exclusively despite their tendency to lose resolution at the edges of the field of view, creating a distorted image. The problem arises in attempting to provide a two-dimensional represen- tation of the three-dimensional world around us. Think of the difference between a globe and a map of the world. On a globe, continents appear in the correct proportion based on their position on the Earth and their relative sizes compared with other continents. Depending on the type of projection that’s used to translate that 3D sphere into a 2D map, some countries and continents appear dis- torted and out of proportion.
In a rounded representation, objects located at
either pole are squished and it may be difficult to read any print that appears on them. This is the same kind of effect a fisheye lens produces. With a fisheye lens, the farther an object is from the center of an image, the more narrow (distorted) it becomes. This can be overcome with software, Peterson says, but because of the required time and
Do You Need a Megapixel Lens?
When using a megapixel camera, you have two choices: use a megapixel lens or use a standard lens. Both will technically work, but a megapixel lens will work much better, and as a result is more expensive. Todd Pinnell, product manager at Amityville, N.Y.-based Speco Tech- nologies, cautions against using price as a determining factor. Rather, he suggests that if you require a high-resolution image, quality matters. So you should be looking at a higher-end lens from a trusted manufacturer, even if it’s more expensive. After all, he says, you get what you pay for. “The smallest imperfection on a megapixel lens will cause the shot to look terrible,” he describes.
Although you can use a standard lens with a megapixel camera, Pin- nell warns against it. However, if you must to go that route, be aware of the potential for image deterioration at the outer ridge of the shot. Megapixel lenses, he says, correct the issue.
82 November 2010
processing power, that may not be the best option. Additionally, he says, those objects at the edges of the image already have been compressed and the information lost as it traveled through the lens. Another possible solution is to use a newer kind of lens called a rectilinear lens. Revisiting the globe-to-map example from above, the effect produced by a rectilinear lens is the same as a world map on which objects at the poles appear proportionally larger than they should be. Think of the monstrous size of Antarctica and Greenland on some maps and you’ll have an idea of this. However, unlike on a map, enlarging objects at the edges of an image is actually a good thing, Peterson says. The 3D “stretching” created by the lens cre- ates increased resolution at the edges of the image, making it more valuable from a security standpoint. Unfortunately, says Glenn Wolk, president of
Tekstar Optical, based in Kings Park, N.Y., distor- tion isn’t just limited to wide-angle lenses. Aside from pairing the wrong type of lens with the wrong type of camera, Wolk points to light levels as one of the main culprits. According to Wolk, a lot of installers or integra-
tors don’t think about the variation of the camera’s aperture across the full range of the lens. When they look at the f-number (which compares the length of the lens to its diameter), they look for the lowest number — assuming, naturally, that a lower f-number indicates a faster aperture and brighter light. However, he cautions, that’s not always the case because that f-number — and hence the lens’ light quality — is achieved only at the widest angle. So if you think you can judge a lens’ performance by looking at the spec sheet, think again. The varia- tion in performance across the entire lens — and the way it’s reported — has become somewhat of a frustration for many in the industry, Bard says. “A lot of times, it’s hard to even find what’s being disclosed as far as specs,” she thinks. A specific piece of information Bard says is often conspicuously absent is the pixel count between the camera and the lens. Because some manufacturers bundle the two, it’s easy not to have that listed on the data sheet, she explains, but that means an installer has to call the manufacturer to get that in-depth infor- mation — if they’re even aware of its importance. “You really have to put your faith into your
manufacturer,” Bard relates. “There’s a lot more information available now than a year ago, but it’s still not all there.” In the same vein, Iniguez points to the claims lens manufacturers make about resolution, which
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