Terminology/Technical Reference Image sizes ia go na l:Ｄ There are several types of imaging elements for CCTV cameras, with different image sizes. The aspect ratio of CCTV camera is normally 4:3 (H:V). Imaging element D Product symbol 1″ 2/3″ 1/2″ 1/3″ 1/4″ Vertical:Ｖ Horizontal:Ｈ Image size（mm） Horizontal：H Vertical：V Diagonal：D C 1″ 12.8 9.6 16.0 H 2/3″ 8.8 6.6 11.0 D, S 1/2″ 6.4 4.8 8.0 Y, T 1/3″ 4.8 3.6 6.0 Q 1/4″ 3.6 2.7 4.5 35mm Camera Lens（Reference） 35mm Film 36.0 24.0 43.3 C/CS-mount CCTV cameras have either the C-mount or the CS-mount. Standard Flange back focal length（mm） C-mount CS-mount 17.526 ＊1 12.5 ＊1 Diameter of screw thread（mm） Interchangeability 1-32UNF C-mount camera CS-mount camera C-mount lens ○ ○＊2 CS-mount lens × ○ ＊1 Length in air ＊2 Will need a C-mount adapter ring（5mm）when fitting a C-mount lens to a CS-mount camera. TERMINOLOGY/ TECHNICAL REFERENCE Focal Length Flange back and back focal distance Flange back will be the distance between the mechanical mount surface and image plane. Back focal distance will be the distance between the rear end of the lens part to the image plane. The focal length will be the distance from the back principal point to the image plane. Lower the focal length the wider the image can be photographed. Back Principal Point Image Plane Image Plane Focal Length Back Focus(B.f) Frange Back(F.f) J-2 Terminology/Technical Reference Exit pupil position Distortion Distortion is an aberration where the geometric figure of the object is not reproduced faithfully at the image plane. It is normally represented by the level shift of an image point from its ideal position by a percentage of image height or width. Exit pupil is the image (virtual image) reflected by the lens located at the back of the lens diaphragm. Exit pupil position is generally represented with the distance between the image surface and the exit pupil. Exit pupil Barrel Distortion Image surface Pin-Cushion Distortion Lens Lens diaphragm Object Exit pupil distance Brightness of a Lens（F and T Numbers） The F number is an indication of the brightness of lens. The smaller the value, the brighter the image produced by the lens. The F number is inversely proportional to the effective diameter of the lens and directly proportional to the focal length. F No.＝ f d The scale on the iris ring of lens uses a ratio of 2, because the value of light incident on a lens is proportional to the cross section of luminous flux（square of diameter）. In other words, the brightness decreases by half each time the F number is increased by one F stop. The F number is a value determined on the assumption that the transmittance of the lens is 100%. Virtually all lenses however, have different spectral transmittance, and thus, the same F number can have different levels of brightness. To eliminate this inconvenience, a system has been developed to consider both F number and spectral transmittance, the T number. The T and F numbers are related to each other as follows: T No.＝ f：Focal length of a lens d：Effective diameter of a lens F No. Transmittance TERMINOLOGY/ TECHNICAL REFERENCE MTF（Modulation Transfer Function） 100 MTF（Modulation Transfer Function）represents the declining contrast rate when shooting a chart consisted of black and white line width. MTF % 80 60 40 20 0 Frequency MHz J-3 × １０ Terminology/Technical Reference 3CCD Camere Lens 100 80 MTF % Common 3CCD cameras have a ticker glass protection than a single CCD camera between the lens and the CCD because three CCDs are placed to correspond with the red, blue and green color separation. Therefore, if a lens intended for a single CCD camera is used on a 3CCD camera, the performance will not be as high as expected due to the efect on the optics structure inside of the camera. Fujinon 3CCD lens are designed to match perfectly with the common 3CCD cameras in the market today. The chart shown at the right explains the difference in MTF when a single CCD lens and a 3CCD lens is put on the 3CCD camera. 3CCD 60 Single CCD 40 20 0 Center Diagonal Image Height Fixed focal length lens corresponding to megapixel 100 80 MTF % We have realized a high resolution compact lens corresponding to mega pixel by adopting the high technical skills cultivated from broadcast lenses and optical beam splitters. The chart shown at the right compares MTF of an ordinary CCTV lens and a mega pixel corresponding lens. As the frequency increases, the disparity in MTF becomes bigger. 60 40 20 0 Frequency MHz Megapixel Lens Ordinany Lens The angle of view is the shooting range that can be viewed by the lens given a specified image size. Normally the angle of views is measured assuming a lens is focused at infinity. The angle of view is obtained by calculation if the focal length and the image size are known. Ｈ θ ：Angle of view Y'：Image size f ：Focal length θ Image surface Rear principle point Example The angle of view at the side of the image when the camera size is 1/2" and the focal length is 12.5mm: θ θ Front principle point Y'：6.4 f ：12.5 6.4 θ＝2tanｰ1 ＝28.72° 2×1 2 . 5 J-4 Image size Y' θ＝2tanｰ1 2f Ｄ TERMINOLOGY/ TECHNICAL REFERENCE Angle of view Terminology/Technical Reference Field of view If the object distance is limited then the field of view can be calculated from the following formula. Y L Y＝Y'・ f Y ：Objects size Y' ：Image size L ：Distance from lens to object f ：Focal length of the lens Y′ L f Example The horizontal size where the object can be fully projected on the monitor when the camera size is 1/2", the focal length is 12.5mm, and the distance from the lens to the object is 5m: Y'：6.4 L：5000 f ：12.5 5000 Y＝6.4× ＝2560mm 12 . 5 Depth of Field When focusing on, a certain area in front of and behind the deep object appears in focus. This area is called the depth of field. This is because the focus appears in sharp if the focus misalignment is under a certain quantity. This certain quantity is called the permissible circle of confusion. The depth of field can be calculated by the following formula. Backward Depth of Field Tr＝ δ・F・L 2 f −δ・F・L Forward Depth of Field δ・F・L 2 f ＋δ・F・L Tf＝ 2 2 The depth field has following properties. Depth of field ＝Tr＋Tf 1）The larger F number is, the wider the depth of field becomes. Focal Depth ＝2δ・F 2）The shorter the focal length is, the wider the depth of field becomes. f ：Focal Distance F ：F number δ：Permissible Circle diameter of Confusion L ：Object Distance 3）The longer the distance to the object is, the depth of field becomes. 4）The backward depth of field is wider than the forward depth of field. 1" Permissible Circle of Confusion（mm） 0.04 2/3" 0.028 1/2" 0.02 1/3" 0.015 1/4" 0.011 Tr Tf Depth of Field Focal Depth J-5 TERMINOLOGY/ TECHNICAL REFERENCE Image size Permissible Circle of Confusion

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