Some CCTV cameras are sold by bundling together the cameras with lenses, housing, cable and other necessary accessories. But other cameras require separate selection and purchase of a lens, which can include fixed focal length, variable focal length, megapixel, pinhole and 360-degree lenses, among others.
How should security professionals identify the types of applications for which those lenses are best suited?
FIXED FOCAL & VARIFOCAL LENSESAmong the best-known lenses are fixed focal and varifocal. Fixed focal â€” an industry standard â€” is just what the name suggests: lenses with focal lengths of 1.3 millimeters up to 100 millimeters that are not adjustable.
John Moroney, product manager, CCTV lenses, for Wayne, N.J.-based Fujinon, reports that fixed-focal-length lenses are best suited for security applications where video is recorded and used after the fact in the investigation of a crime, or to defend a “slip-and-fall” lawsuit. “It’s not monitored live, so it’s never adjusted,” Moroney says.
Variable-focal-length lenses are another kind of lens used in the same applications as fixed-focal-length lenses, Moroney says. “But because they’re varifocal, they are flexible. A dealer can take a single lens and use it on a lot of different cameras in different applications, just by adjusting it. With a varifocal lens, you have this one lens and you just dial in the subject’s distance from the camera and forget about it. It then becomes a fixed-focal lens in the application. Varifocal has pretty much replaced fixed focal as the lens of choice for CCTV applications in which the video is not monitored.”
Prior to the development of the varifocal lens, an integrator had to go to the site with two to four types of lenses, screw on each lens and determine from the customer whether the resulting view was the one desired. By contrast, the varifocal lens lets integrators take one lens to the site, screw on and adjust the lens, and determine from the customer whether the view from the adjusted lens is the correct one.
In the early years of the varifocal lens, two factors prevented it from being widely accepted. One was its comparatively high cost, and the other that the early lenses’ 8- to 16-millimeter focal length dimensions made wider fields of view impossible.
By the mid 1990s, however, cost had decreased, and 3.5- to 8-millimeter varifocal lenses had rendered wider fields of view a reality.
“Many security applications call for a wide field of view, because security managers only want to see if any anomalous activity is occurring,” says Steve Beaulieu, national sales manager with Commack, N.Y.-based Tamron USA, whose industrial optical division makes lenses for the CCTV industry and factory automation.
Companies including Tamron and other manufacturers proceeded to develop new varifocal lenses. For example, there was a need for a telephoto lens, so Tamron unveiled a 5- to 50-millimeter lens in the late 1990s. The benefit of a telephoto lens is for making distant objects appear magnified. The longer focal length (50mm) corresponds to the telephoto aspect. In 2001, Tamron introduced a 2.8- to 12-millimeter varifocal lens that covers 80 percent of security applications, Beaulieu estimates. A 2.8-millimeter focal length provides a wider angle.
Also in the early part of this decade, camera manufacturers began introducing day/night cameras, which led to the need for infrared (IR)-corrected varifocal lenses for use with day/night cameras in outdoor applications.
Varifocal lenses have been the industry standard for 14 years, says Tom Harada, managing director, and Jonathan Barnthouse, account executive, with Pentax US Security for Pentax Imaging Company, Golden, Colo. Varifocal lenses are employed in all areas of security, including in the retail and financial services industries.
They are often used on box cameras, which banks prefer because they are visible and identifiable as cameras, and therefore act as a deterrent to crime. The range of 2.8 to 12 millimeters permits the adjustment of the camera’s field of view.
Megapixel lenses, which can be fixed-focal-length or varifocal, are designed for use on megapixel cameras. “To accurately describe each pixel, you need a camera and a lens equally rated to identify each of the pixels,” Moroney explains. “Your picture will only be as good as your weakest link.
“If you have a 5-megapixel lens on a 1-megapixel camera, you’ll get a great 1-megapixel image. If you have a 1-megapixel lens on a 5-megapixel camera, you’ll get 5-megapixel worth of data from the camera, but only one will be identified by the lens â€” the other four extrapolated from the software.”
To illustrate, Moroney notes that a purple spot on a blue background is more difficult to see than a black spot on a white background. If the spot is small enough or too similar in color to the contrasting background, the imager seeing through a lower-resolution lens will pick bluish/purple pixels, rather than select true blue or true purple pixels, depending on where the spot begins and ends. The imager’s ability to distinguish patterns and colors is limited by the lens. The imager will still create the number of megapixels its camera setting dictates. However, it will not have the clarity to accurately see the correct detail for each pixel that it would be capable of capturing were the optics of equal or greater resolution quality, Moroney explains.
MEGAPIXEL LENSES“What makes a megapixel lens is the design and quality of the optics that allow the rays of light of the spectrum to be focused to a point on a pixel; the better they are focused on the pixel, the crisper the image, the better the resolution,” notes Andrea Iniguez, vice president of business development at Theia Technologies, Wilsonville, Ore. “As you go up in numbers of pixels, they become smaller to fit into the same area. The challenge is to focus the rays of light on smaller and smaller (for example, 3 micron size) pixels. A poor-quality megapixel lens is one that is not able to focus the rays of light well on the pixel, resulting in blur, color aberration, or other distortion,” she says.
In actual application, using a varifocal megapixel lens is “like going from standard television to high-definition television,” Beaulieu says. “What it allows you to do is use fewer cameras. Say you’re covering a 90-degree angle. It could be in a bank where instead of using five cameras, you now only use two. You’re able to digitally zoom at a later time, and still see a clear image, as opposed to a pixelated image.”
If the angle being viewed is less than 70 degrees, conventional megapixel lenses are adequate. For wider viewing areas, a rectilinear megapixel lens is beneficial, say Iniguez and Jeff Gohman, president of Theia Technologies, which specializes in rectilinear lenses.
“When people want to see a wide area with high definition, they use a megapixel camera,” Gohman says. “But with a typical lens, as you move out on an angle, you get fewer and fewer pixels per degree of the field of view due to barrel, or fisheye distortion. The rectilinear lens corrects the barrel distortion with the optics, so you don’t lose information. You keep as many pixels per degree as you move out towards the edge.”
Applications for the rectilinear megapixel lens are in settings such as parking lots, intersections, warehouses, building egress and entry points, supermarket checkout scans, and the entire width of a jail cell where a wide angle can be viewed with one camera as opposed to three. “With fewer cameras they have a lower installation cost, lower cost of cameras, lower cost of cabling, and lower cost of monitoring and maintenance,” Gohman says.
PINHOLE LENSESA normal lens has a glass opening of from 3/8 to ¾-inch diameter, says Gary Perlin, vice president of video products for Amityville, N.Y.-based Speco Technologies, which makes lenses of all types for CCTV surveillance applications. By contrast, a pinhole lens is normally limited to 1/16 inch. The small opening allows users to easily conceal the camera on which the lens is attached, because it requires only a very small diameter hole to operate.
“The tradeoff is much less light is getting to the camera, so you have to compensate by adding more light to the scene, or by using a low-light-level camera,” he explains.
A pinhole lens might be used on a camera positioned to capture a hotel lobby. “There’s no expectation of privacy there, but you don’t want to hang a camera from the ceiling and give guests the impression they’re in a penitentiary,” Perlin says.
360-DEGREE LENSESAccording to Alessandro Gasparini, senior vice president of sales and marketing and chief commercial officer for Montreal-based ImmerVision, 360-degree lenses are used to see a wide area without blind spots (such as in the photo below). “For example, the guard can monitor a 10,000-square-foot area without blind spots to detect intrusions from any side, and to recognize the [nature of the intrusion],” Gasparini reports.
“Then he can use a good quality pan-tilt-zoom camera equipped with a high zoom lens to identify the intruder before sending in a patrol. In [settings such as] retail, banking, hospitals, universities and any public or private places where numerous CCTV cameras are already found, we see the use of 360-degree lenses with either standard analog/IP VGA or low-megapixel cameras to remove any potential blind spot and to relate events and people in one single coherent view.”
What’s more, 360-degree lenses are used to detect perimeter intrusions and threatening behaviors in high-security settings like utilities, airports, seaports and government buildings. Additionally, 360-degree lenses posted on high towers are invaluable in managing traffic and crowds. When accidents or incidents occur, police can rapidly reconstruct event sequences from that one view, Gasparini describes.
“Three-hundred-sixty-degree panoramic lenses are the only lenses that, when added to either existing standard analog cameras or new IP systems, provide users with complete situational awareness.”