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Focal Length Angle of View F-Number Field of View Technical Information CCTV is widely accepted as an important and valuable tool in many areas. Manual iris lenses for constant, stable lighting conditions and auto iris lenses for variable lighting conditions. Select the best suited lens for optimum performance in each application. Focal Length Rays from infinitely distance objects are condensed internally in the lens at a common point on the optical axis. The point at which the image sensor of Secondary principal point the CCTV camera is positioned, is called a focal point. By virtue of design, lenses have 2 principal points, a primary principal point & a secondary principal point, the distance between the secondary principal point and the focal point (image sensor) determines the focal length of the lens. Primary� principal point Focal length Focal point /� Image sensor Angle of View The angle formed by the 2 lines from the secondary principal point to the image sensor is called the angle of view. Therefore, the focal length of the lens is fixed regardless of the image format size of the CCTV camera. Secondary principal point Conversely, the angle of view varies in accordance with the image size. The focal lengths in the catalog are nominal and the angles of view calculated by θ� D the formula referring to the focal lengths are approximate. D� θ＝2×tan-1� 2f Focal length f Image sensor F-Number The F number is the index for the amount of light that passes through a lens. The smaller the number, the greater the amount of light. The F number is a ratio between focal length and effective aperture as follows. f f�＝�focal length� F Number ＝ D D ＝�effective diameter Field of View he field of view varies along with the focal length of the lens as follows. W�：�width of object� H�：�height of object� w�：�width of format� ��1/2 format = 6.4mm, 1/3 format = 4.8mm,� ��1/4 format = 3.6mm� h�：�height of format� W/H w/h ��1/2 format = 4.8mm, 1/3 format = 3.6mm,� ��1/4 format = 2.7mm� f�：�focal length� L ：�object distance� L f � Example ： Full image of 4.5m-high object on a TV monitor w� h� f� ＝� ＝� camera: 1/3 format, Object distance: 10m� Technical Information W H L H = 4.5m = 4,500mm L = 10m = 10,000mm h f 3.6 f ＝� ＝� f＝8mm H L 4,500 10,000 Technical Information Close-Up Application 1）Extension Tube（Macro Ring）� When the rays originate from a finite object distance, the rays are condensed at a point further than the focal point, while the rays from infinite Infinite rays Image sensor distance are condensed at the actual focal point. The focus adjustment moves the lens barrel toward the object to shift the focusing point at the image sensor. However, the amount of focusing adjustment is mechanically limited as sees by the minimum object distance. Extension Tube (Macro Ring) is inserted in between the lens and camera to shift the focus point Finite rays further than the mechanical limit for close-up focus. 2）Close-Up Lens� The close-up lens has a positive meniscus lens as a supplementary lens. Generally, 3 types of close-up lenses are available, close-up lens No.1, 2 & 3 have 1,000mm (1,000mm/1), 500mm (1,000mm/2), 333mm (1,000mm/3) respectively. When an object is placed at the focal point of the close-up lens, Focal length� the rays from the object are converted by the close-up lens to be parallel of close-up lens rays against the optical axis as seen on the right. This lens is effective when wishing to come closer to an object than the min. object distance of a lens, or taking close-up pictures of small objects. Depth of Field When an object is focused, it is typically observed than the area in front and behind the object is also in focus. The range in focus is called Ågdepth of fieldÅh. When the background is extended to infinity, the object distance (focusing distance) is called Åghyper focal distanceÅh. Depth of field is calculated by using the following formula. F�=�F No.� 2 f � H＝ H�=�hyper focal distance� C × F f�=�focal length� B�=�object distance (measured from image sensor)� T1�=�near limit� B（H＋f）� T1＝ T2�=�far limit� H ＋ B C = circle of least confusion� 1/2 format = 0.015mm, 1/3 format = 0.011mm,� 1/4 format = 0.008mm B（H－f）� T2＝ Depth of field increases when:� H － B ＊Focal length is shorter� ＊F-number is larger (F/1.4 ＜ F/5.6)� ＊Object distance is longer CS and C mount CS mount as present CCTV market standard is specially designed for CCTV （flange back）� camera lens developed by PENTAX. This is to minuturize the size and to CS mount lens 12.5 CS mount camera improve the performance of lens by shortening the flange back by 5mm comparing to C mount.C and CS mount lenses are available in the present market, and CS mount is only applicable to CS mount camera.C mount lens is applicable not only to C mount camera but also to CS mount camera by using 5mm Adapter Ring (as C-CS-A ). CS mount camera Mount Surface C mount lens Focusing Plain Technical Information 5 spacer 17.5 TECHNICAL INFORMATION TECHNICAL INFORMATION Camera Format ANGLE OF VIEW The size of camera’s imaging device also affects the angle of view, with the smaller devices creating narrower angles of view It is important to know the angle of view of the lens to take in the object. Angle of view changes with focal length of lens and when used on the same lens. The format of the lens, however is irrelevant to the angle of view, it merely needs to project image size of camera.The focal length to cover the object can be calculated from the next formula. an image which will cover the device, i.e.; the same format of the camera or larger. This also means that 1/3” cameras can utilize the entire range of lenses from 1/3” to 2/3”, with a 1/3” 8mm lens giving the same angle as a 2/3” 8mm lens. The latter combination also provides increased resolution and picture quality as only the centre of the lens is being utilized, where ● Formula for calculation ● For example the optics can be ground more accurately. (1) in case of vertical size f : focal length of lens 1/2 inch camera v = 4.8mm V : Vertical size of object Vertical size of object V = 330mm(33cm) Distance from lens to object D = 2500mm(250cm) H : Horizontal size of object substitute these datas to formula (1) D : Distance from Lens to object v : vertical size of image (see the following table) h : horizontal size of image (see the following table) (2) in case of horizontal size 1/2 inch camera h = 6.4mm Horizontal size of object H = 440mm(44cm) D = 2500mm(250cm) FORMAT 2/3inch 1/2inch 1/3inch 1/4inch Distance from lens to object substitute these datas to formula (2) v 6.6mm 4.8mm 3.6mm 2.7mm h 8.8mm 6.4mm 4.8mm 3.6mm Focal Length ■ COMPARISON OF MONITORING IMAGES ※Images on 1/3"camera Object distance The focal length of the lens is measured in mm and directly relates to the angle of view that will be achieved. Short focal 2m 5m 10m 20m length provides wide angle of view and long focal length becomes telephoto, with narrow angle of view. A "normal" angle of Focal length view is similar to what we see with our own eye and has a relative focal length equal to the pick up device. The "computar" range calculator is simple device to use for estimating focal length, object dimension and angle of view, alternatively the VM300 view finder gives an optical way of finding focal length. f=2.8mm f=3.5mm f=8mm TECHNICAL INFORMATION TECHNICAL INFORMATION f=30mm F S t o p The lens usually has two measurements of F stop or aperture, the maximum aperture (minimum F stop) when the lens is fully open and minimum aperture(maximum F stop) just before the lens completely closes. The F stop has a number of effects upon the final image; a low minimum F stop will mean the lens can pass more light in dark condition, allowing the camera to produce a better image, and a maximum F stop may be necessary where there is a very high level of light or reflection, this f=50mm will prevent the camera "whiting out" and maintain constant video level. All auto iris lenses are supplied with Neutral Density filters to increase the maximum F stop. The F stop also directly affects the depth of field. 28 TECHNICAL INFORMATION TECHNICAL INFORMATION Camera Format ANGLE OF VIEW The size of camera’s imaging device also affects the angle of view, with the smaller devices creating narrower angles of view It is important to know the angle of view of the lens to take in the object. Angle of view changes with focal length of lens and when used on the same lens. The format of the lens, however is irrelevant to the angle of view, it merely needs to project image size of camera.The focal length to cover the object can be calculated from the next formula. an image which will cover the device, i.e.; the same format of the camera or larger.
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