T3.1 in samyang is equivalent to what aperture in canon and nikon?

T3.1 in samyang is equivalent to what aperture in canon and nikon?

3.1. Aperture is aperture regardless of manufacturer.

But T-stops are not exactly the same thing, http://en.wikipedia.org/...ber#T-stop shows that this lens probably has an f-stop of f/2.8 or so.

A "t/stop" reflects the actual amount of light that reaches the film or sensor and is necessary when using an external incident lightmeter (lenses, especially zoom lenses, eat some light) An f/stop is a theoretical number which reflects the size of the lens opening as a fraction of the focal length of the lens.

If you are using an internal lightmeter, then it does not matter if the lens has simple f/stops or calibrated t/stops

I have a feeling that the answer is more complicated than one may think. I would assume that the size of the sensor will have an affect on the relationship between a T & F stop.