Glossary
Glossary lens| Telecentric optical system | An optical system in which the chief ray is parallel to the optical axis on either or both the object side and the image side. This has the advantage that the size of the captured image does not change even if the object position or image position on the side where the chief ray is parallel shifts in the direction of the optical axis. |
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| Distortion | Aberration in which the shape of an object on a plane perpendicular to the optical axis expands and contracts at the periphery of the image. There are three types: pincushion, barrel, and crooked.
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| optical distortion | The change in image height due to distortion is divided by the ideal image height assuming no distortion, and expressed as a percentage. The value shown in the catalog is the maximum value within the field of view of the compatible camera. |
| TV distortion | A percentage value that indicates the amount of curvature of a straight line image due to distortion on the long side of the image sensor. It is used to indicate the amount of distortion in CCTV lenses for surveillance cameras, projection lenses, etc. It is often about 1/3 of the optical distortion. |
| chromatic aberration | This is an aberration in which the position of an image formed along the optical axis and its magnification differ depending on the wavelength of light. The difference in the position of an image formed along the optical axis is called axial chromatic aberration, and the difference in magnification is called lateral chromatic aberration. |
| optical resolution | The minimum distance on an object surface at which two points of the same brightness can be distinguished using an optical system. Two points closer than the optical resolution are usually not distinguishable as a single point. Example: 10μm → 5μm black and 5μm white can be resolved within 10μm. |
| resolution | This value indicates how fine an image of equally spaced black and white lines can be distinguished, expressed as the number of pairs of black and white lines (lines/mm) that fit within a 1 mm width on the image plane. It is mainly used in CCTV lenses for surveillance cameras. |
| depth of field | The range in which the subject remains clear even if it moves back and forth along the optical axis. The range of depth on the object side. *Clear range = OPTART defines it as the range in which resolution is guaranteed. |
| depth of focus | The range in front of and behind the lens image plane in which an image can be captured clearly without blurring. This refers to the range of depth on the image side. |
| Numerical aperture NA | It is a quantity that indicates the brightness and optical resolution of an optical system. The larger the NA, the brighter and the higher the resolution. If the magnification is the same, it is brighter. When the angle that an object point on the optical axis in a medium with a refractive index of η makes with the radius of the entrance pupil is α, the numerical aperture (NA) is expressed as η sin α. Object-side numerical aperture = NA, image-side numerical aperture = NA'. *The NA listed in our catalog is all object-side numerical aperture (NA). |
| Vignetting | When a certain amount of light (object) is taken in by an optical system, it is expressed as the ratio of the brightness of the periphery to the central brightness of 100%. |
| Aperture ratio | The ratio of the entrance pupil diameter of an optical system to the focal length. |
| Working distance WD | The distance from the tip of the lens barrel to the object plane on which focus is achieved. |
| Image Circle | The circular area on the image plane where the image forming performance and brightness are considered to be good. Imaging circle size = CCD diagonal size. *Image size is a synonym. |
| Image size | The vertical and horizontal or diagonal dimensions of an image surface element. |
| permissible circle of confusion | A circle whose diameter represents the permissible blur of a point image. The diameter of the permissible circle of confusion is used to calculate the depth of field. |
| F-number | A value that indicates the brightness of a lens when photographing an object at infinity. The brightness of the image is inversely proportional to the square of the F-number, and the smaller the value, the brighter the lens. *Used for CCTV lenses and photographic lenses. |
| Effective F-number | A value that indicates the brightness of a lens when photographing a close-up object. Image brightness is inversely proportional to the square of the effective F-number, and the smaller the value, the brighter the lens. *Used for machine vision lenses. |
| MTF | A value that indicates the degree to which an optical system can reproduce the shape of an object. It is equal to the contrast response value when an object with a sine wave-like change in brightness is imaged. It may be substituted with the contrast response value obtained from the shooting results of a square wave chart with equally spaced black and white lines. *Spatial frequency = number of lines on a resolution chart |
| flange back | The distance from the camera mount's reference mounting surface (flange) to the image plane. The distance is specified depending on the type of mount. |
| back focus | The distance from the last refracting surface of a lens to the focal plane where an image of an object at infinity is formed. |
| C mount, JEITA standard | One of the standards for lens mounting screws and flange focal distances specified in JEITA TT-4506A (revised January 2014).
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| Difference between C mount and CS mount |
*When attaching a C-mount lens to a CS-mount camera, please attach a 5mm C-mount adapter. |
| Relationship between lens F value and brightness |  |
