CCTV SYSTEMS CAMERA LENSES
CCTV SYSTEMS • A camera lens is more than just a piece of glass. • A lens is an optical device that collects reflected light and focuses the light on the cameras image sensor to construct an image.
CCTV SYSTEMS • Lenses have several attributes that are critical to it’s effective operation, these are: • SIZE • MOUNT TYPE • FOCAL LENGTH (FL) • FIELD OF VIEW (FOV) • IRIS • MAGNIFICATION
CCTV SYSTEMS • The lens size is partially determined by the type of camera. • Different sizes require different mounting requirements though they operate the same. • The lens size refers to it’s form factor. • The form factor is the physical dimension of the lens housing and mount.
CCTV SYSTEMS • Most out of the box systems have cameras that provide images that are the equivalent of what the human eye would see. • They’re not adjustable and provide no additional magnification or resolution options.
CCTV SYSTEMS • When considering the lens size, the focal length (FL) and field of view (FOV) are also important.
CCTV SYSTEMS • The lens mount connects a lens to a camera. • There are several standard mount types, the most common are the C and CS mounts. THE THREADED PORTION OF THE LENS IS THE MOUNT
CCTV SYSTEMS • The most common mount of the two is the C mount. • It is a 1 inch diameter hole with 32 threads per inch.
CCTV SYSTEMS • As a standard the C mount will accommodate all 1/4, 2/3 and 1 inch cameras. • the CS mount was created for CCD cameras and other smaller formats and it accommodates ¼, 1/3 and ½ inch cameras.
CCTV SYSTEMS • There is some degree of interoperability between a C and CS mount lenses, provided a 5mm spacer is used. • the spacer allows the correct positioning of the lens at the proper distance from the image sensor. • This distance is referred to as the pitch. CS TO C MOUNT ADAPTER
CCTV SYSTEMS • a CS mount cannot be mounted on a c mount camera, there is no way to compensate for the 5mm difference.
CCTV SYSTEMS • LENS FORMATS – Is the approximate size of a camera image detection device. • This term is used to determine the size of lens that can be used on various types of cameras. • A 1" format lens will work on a 1", 2/3", 1/2", 1/3", 1/4" (and down) size cameras.
CCTV SYSTEMS • A smaller format lens will not work well on a larger format camera. • Using a smaller format lens on a larger camera causes distortions ranging from tunnel vision to poor back focus. 1/3”Lens ¼” Lens ½” Lens
CCTV SYSTEMS • There are two standard lens types in use: 10mm and 12mm diameter formats, other lens mounts are typically non-standard.
CCTV SYSTEMS HERE IS A PHOTO USING DIFFERENT LENS FORMATS FROM THE SAME DISTANCE WITH THE SAME CAMERA 4.3MM LENS 6MM LENS 8MM LENS 12MM LENS 16MM LENS
CCTV SYSTEMS • Focal length (FL) is a measurement of the image sensing area and is measured in millimeters. • The focal length determines how much magnification a lens provides.
CCTV SYSTEMS • The focal length of the lens is determined by the focal center of the lens and the convergent focal point.
CCTV SYSTEMS • A shorter focal length lens will be able to see a wider angle of view on a scene. • A longer focal length has a narrower angle of view on the scene, but a higher level of magnification.
CCTV SYSTEMS • A fixed focal length (FFL) is used in most CCTV applications. • It is important to match the focal length based on the form factor for your camera. (1/4, 1/3, ½ or 1 inch)
CCTV SYSTEMS • Varifocal lenses have to be manually adjusted by the installer. • This requires a small test monitor while adjusting the focus of the lens.
CCTV SYSTEMS • Varifocal lenses have thumb screws to loosen the lens adjustment and can be tighten down to maintain the desired setting. THIS LENS HAS AN AUTO IRIS CONNECTOR TO ADJUST FOR INCOMING LIGHT.
CCTV SYSTEMS • The field of view (FOV) is the maximum angle of view, as the field of view increases, magnification decreases. • The same magnification as the human eye would have an FOV of M=1.
CCTV SYSTEMS • The iris of the camera lens adjusts the amount of incoming light that passes through the lens.
CCTV SYSTEMS • The parts of a camera lens iris.
CCTV SYSTEMS • An automatic iris opens and closes itself when the amount of light moves beyond a certain threshold. a manual iris is controlled by an operator. NOTICE THE “f” LISTED NEXT TO EACH PICTURE, THIS IS THE F-NUMBER.
CCTV SYSTEMS • The aperture is the "opening" of the lens, the size of which is controlled by the iris and is measured in F numbers. • Generally, the lower the F number, the larger the aperture and consequently more light can pass through the lens.
CCTV SYSTEMS • Cameras with automatic gain control (AGC) are able to use a fixed iris lens. • AGC is a camera feature that adjusts the incoming light much like an automatic iris. • Cameras with AGC increase the video signal under low light conditions.
CCTV SYSTEMS • Contrast AGC with automatic light control (ALC), a form of backlight control and ALC makes a brighter image to add detail in darker portions of the image.