Wide Angle Lenses
| By: Mark Peterson and Andrea Iniguez
HD and megapixel cameras have many advantages as long as you have the right lens for the job. When that includes covering large areas or reducing cost by installing fewer cameras, that lens is a wide angle lens. Wide angle lenses are not a panacea, but there are many applications that benefit from their use. For applications requiring large areas of coverage, an ultra-wide angle lens on a megapixel camera is a cost saving opportunity that should be considered. Wide angle lenses can
- reduce the number of cameras required to cover an area, reducing cost of installation, maintenance and monitoring,
- be used in place of a PTZ camera when post-incident digital PTZ is desired,
- effectively monitor large areas like parking lots, schools, and construction sites, and
- be used in close-up applications such as ATMs, card-locked garage entries, and multi-door entryways where both high image detail and wide fields of view are required.
Until recently only fisheye lenses were available for an ultra-wide field of view. Fisheye lenses have the well-known barrel distortion seen in almost all wide angle lenses with fields of view greater than 80 degrees. This distortion causes the image to look curved and resolution to be reduced as the object moves farther from the center of the image. The distortion effect can be eliminated with software (creating a rectilinear lens image), but at a cost in time or processing power. Objects at the edges of the image are compressed and detail information is lost. The information was already lost travelling through the lens and software is not able to recapture the information (contrary to Hollywood’s view of video surveillance).
By contrast, Theia Technologies has developed a family of rectilinear lenses giving a different ultra wide view without the barrel distortion or loss of edge resolution of fisheye lenses. Rectilinear lenses keep straight lines in the real world straight on the image sensor. This creates an effect called 3D stretching or lean-over in which objects at the image edge seem to be stretched because they are being “flattened” onto a plane. The wider the field of view (for rectilinear lenses), the more noticeable is this effect. Rectilinear lenses possess an additional benefit in providing increased resolution at the edges of the image because of 3D stretching.
HD and megapixel cameras need high performance wide angle lenses that can display high-resolution images of large areas. Fisheye lenses create barrel-distorted curved images requiring software image correction whereas rectilinear lenses correct distortion optically in the lens, an elegant and efficient solution.
October 10, 2013