T-mount

As a common mechanical interface, the T-mount allows components of various manufacturers to be interchanged and assembled.

Electrical or mechanical connections (such as for autofocus) are generally not provided, although Sigma's YS Mount featured an automatic diaphragm coupling.

Besides cameras, T-mounts are used in optical breadboard prototyping components as well as telescope and microscope attachments.

The T-mount is also a standard way to mount a camera to a microscope to photograph pathological specimen slides or to a 1.25-inch (32 mm) telescope eyepiece.

Since some DSLRs won't meter without electronic lens data, some adapters are now sold fitted with a Dandelion chip which can be programmed to identify the focal length and aperture limits and enable metering and in some cases focal confirmation.

[1] The thickness of the external ring on an adapter is equal to the difference of the flange distance between the T-mount and the corresponding lens mount in order to achieve infinity focus.