Terminology	Explanation
Backfocus	The distance from the rear end of the lens to the camera’s sensor plane.
C mount	A standard for lens mounting threads and flange back distance. It features an outer diameter of 25.4 mm, 32 threads per inch, and a flange back distance of 17.526 mm. Defined by JEITA (Japan Electronics and Information Technology Industries Association).
Image Circle	The maximum image circle in which the lens delivers acceptable image quality on the sensor plane. The image circle size is equivalent to the image sensor’s diagonal dimension.
Image Size	The dimensions of the image sensor, specified by its width, height, or diagonal length.
Imaging Lens	A lens that forms the image produced by an infinity-corrected objective lens onto the sensor of an industrial camera. Also known as a tube lens.
Infinity-corrected objective lenses	An objective lens designed with an infinite image distance (infinity-corrected). It forms a complete image when used in combination with a tube lens.
Köhler illumination	An illumination method in which the image of the light source is focused at the aperture diaphragm position (the front focal plane of the condenser), and the image of the field diaphragm is focused on the specimen plane. This method provides uniform and bright illumination across the specimen.
Microscope	An optical instrument that allows the naked eye to observe a magnified image of a microscopic specimen, first enlarged by the objective lens and then further magnified by the eyepiece. There are various types of microscopes, including stereo microscopes, biological microscopes, and metallurgical microscopes.
Microscope	A type of microscope in which the image captured by a built-in industrial camera is viewed by the observer through a display monitor.
MTF	Modulation Transfer Function This value is typically represented by the Modulation Transfer Function (MTF), which describes how well an optical system can reproduce the shape of an object in terms of spatial frequency and contrast.
Numerical Aperture(N.A.)	An index indicating how efficiently a lens gathers light. A higher numerical aperture results in a brighter image and greater resolution.
Objective lens	The optical system in an optical instrument that first forms an image of the object. In telescopes, a reflective version of this system is referred to as an objective mirror.
Working Distance	The distance from the front end of the lens barrel to the object plane where focus is achieved.