T-mount

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T-mount is a standard lens mount for cameras and other optical assemblies. It is a screw mount using a male M42x0.75 metric thread on the lens with a flange focal distance of 55 mm, and a mating female thread on a camera adapter or other optical component. This thread form is referred to as T-thread. (This should not be confused with the M42 lens mount which is also 42mm, but has a 1mm thread pitch.)

The "T" is said to stand for Tamron, a Japanese manufacturer, who in 1957 made a line of aftermarket camera lenses all using T-mount as a universal fit to 35mm SLR cameras of various manufacturers. The proprietary lens mount of each competitive manufacturer was adapted to the T-mount thread with a simple adapter. Thus a retailer could stock a small number of expensive lenses that would fit a large number of camera brands using a selection of inexpensive adapters.

The T-mount connection is only a mechanical specification. Electrical or mechanical connections (such as for autofocus) are not provided.

Besides cameras, applications include optical breadboard prototyping components, and telescope and microscope attachments. As a common mechanical interface, T-mount allows components of various manufacturers to be interchanged and assembled.