The T mount, also know as T2, T-mount, Taisei mount, or Tamron mount, is a standardized mechanism developed in 1957 by Taisei Kogaku (later known as Tamron) for attaching threaded lenses to cameras. Most camera manufacturers used proprietary mounts which worked only with their cameras and lenses. The T mount was unusual in that the use of an open standard allowed the possibility of a single lens mount that inter-operated between cameras and lenses from different manufacturers. The standard calls for lenses to have a male M42x0.74 metric thread with a flange focal distance (FFD) of 55mm. The term T thread is sometimes used to refer to this type of lens threading. T mounts should not be confused with the M42 mount which also uses a 42 mm metric thread but has a pitch of 1 mm rather than 0.74 mm. T mount and M42 mounts cannot be used interchangeably without damaging the threads.
Cameras generally do not have T mounts. Instead a T adapter or T2 adapter are used between the camera and the lens. On the rear side a T/T2 adapter has a mount appropriate to the brand and model of camera it will attach to. On the front of the T/T2 adapter is a female threaded connector matching the T thread of the lens.
The T mount is a mechanical-only mount, meaning it does nothing beyond physically connect the lens to the camera. It does not transfer electrical signals, autofocus information, or aperture settings.
The T adapter, sometimes called a T-ring, is a single mechanical part. Once the lens and T adapter are mated, it is sometimes necessary to tighten one or more lens barrel set screw. Because of slight differences in thread length between the adapters and the lenses from different manufacturers it was found the T adapter was inadequate because the lens would not always be in an upright position with the markings and controls aligned with the top of the camera.
The T2 adapter, sometimes called a T2-ring, was created to overcome the alignment flaw of the T adapter. A T2 adapter is made from two concentric rings. The outer ring includes the camera-specific mount. The inner ring attaches to the T thread. The two rings are connected by three set screws. When these set screws are loosened, the inner and outer rings can rotate, changing their respective orientation. To use a T2 adapter, the user normally attaches the adapter to the lens; then mounts the lens and adapter on the camera. Once mounted, the set screws are loosened, the lens is rotated into the correct orientation, and the set screws are tightened again. Because of the time required, it was typical for a user with multiple T mount lenses to buy a T2 adapter for each lens so that it would not need to be readjusted with each use.
One last innovation was the second generation Vivitar Series 1 T adapter. It was similar to a T2 adapter but in place of the three set screws it included a mechanical interlocking mechanism between the two rings that could be adjusted instantly by pressing an unlock button. When the button was pressed, the inner and outer ring rotated freely and when the button was released the two rings locked into place. The second generation Vivitar Series 1 T2 adapter was designed for use with the Vivitar Series 1 450mm mirror lens and the ring's packaging called it the "Vivitar Series 1 450mm T-mount Adapter". The original and more common Series 1 T Adapter is the standard T2 variety. While significantly more expensive than a T2 adapter, it allows users with many lenses to use a single adapter rather than needing one for each lens.
Only T2 adapters are commonly available today. Old style T adapters and Vivitar Series 1 T adapters can only be found in the used equipment market.
Note to collectors - Care should be taken when removing a T adapter from a newly obtained vintage lens. While most will be T2 style adapters that can be unscrewed, some may be the older variety that had lens barrel set screws. If the mount will not unscrew, it may be necessary to loosen or remove all lens barrel set screws in order to remove the T adapter without damaging the lens barrel. Once removed, a modern T2 adapter without lens barrel set screws can be used on the lens.
Sigma's YS mount is a variant of T-mount that adds an aperture control pin. YS mount uses the same threads and flange focal distance as T mount, so T-mount adapters can be used on YS mount lenses, though on some lenses there will be an issue of finding a way to keep the aperture pin pushed down so that the manual aperture control works normally. YS mount lenses were available from Sigma, Upsilon, Accura, Polaris, Sun, and other brands.Spiratone sold YS mount lenses and adapters in the U.S. Like T2 adapters, YS adapters have set screws that allow the mount to be rotated. YS mount lenses are often labeled 'YS-AUTO' on the mount.
Japanese company Taisei Kōgaku Kōgyō K.K. (泰成光学工業㈱) introduced the T mount in 1957 with their first interchangeable camera lens, a 135mm f/4.5 (model #280). The company later changed their name to Tamron and still exists today. According to the company, the "T" stands for Taisei. It is often erroneously speculated that the "T" stands for Tamron, but Taisei did not change their name to Tamron until many years after the mount was introduced. Taisei also introduced the original T adapter. Another company, currently unknown, developed the T2 adapter.
Taisei and later Tamron went on to develop a series of interchangeable mounts that included more advanced features. The T mount, however, outlasted the company's later mounts, and continues to flourish even today. Despite being a mechanical-only connector, it finds uses not just for camera lenses but as a standardized method of adapting cameras to use a variety of optical equipment such as telescopes, microscopes, bellows, and slide duplicators.
- Category:T mount - a list of T mount lenses
- Lens mounts - a list of lens mount types
- Tamron - our main article on Taisei Kogaku / Tamron