An iris diaphgram diaphragm is used to regulate the aperture openings. It is a series of metal leaves that are accurately controlled by an intricate system of pins and linkages. It is located within a lens between the elements of ground and polished glass. Eight (8) metal leaves are used to make a typical iris diaphragm.
Iris Diaphragm
The numbers used to designate given apertures of f-stops are based on the diameter of the diaphragm opening and the focal length of a lens. For example:
Lens focal length = 50 mm
Maximum diaphragm opening = 35 mm
Divide the focal length by the maximum diaphragm opening to obtain the f-stop number. Only one (1) decimal place is used, otherwise it would become extremely confusing.
50 mm ÷ 35 mm = 1.429 thus f/1.4
As the diaphragm opening becomes smaller, the f/stop number becomes larger.
50 mm ÷ 0.25 mm = 8.0 thus f/8
The numbers used to designate given apertures of f-stops are based on the diameter of the diaphragm opening and the focal length of a lens. For example:
Lens focal length = 50 mm
Maximum diaphragm opening = 35 mm
Divide the focal length by the maximum diaphragm opening to obtain the f-stop number. Only one (1) decimal place is used, otherwise it would become extremely confusing.
50 mm ÷ 35 mm = 1.429 thus f/1.4
As the diaphragm opening becomes smaller, the f/stop number becomes larger.
50 mm ÷ 0.25 mm = 8.0 thus f/8
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