What's the Difference Between F-Stop and T-Stop?
Everyone has a general idea of what "f-stop" means, despite it also being known as "f-number," "f-ratio," "focal ratio," or "relative aperture." But then there's "t-stop" which is similar but slightly different from f-stop, in that it's a measurement instead of an equation. Richard Schleuning Of Zeiss explains, clearly and concisely, the difference between the two:
[via DV Culture]