If you're new to cine lenses you might be wondering about the T-stops and how they're different from f-stops. The T stands for “transmission” and the T-stop – also called a T-number – is a measure of exactly how much light is passed through the lens (i.e. to the sensor), taking into account the losses which occur in the optical system due to refraction, diffusion or reflection. In comparison, f-stops are determined mathematically by dividing the focal length of the lens by the diameter of the aperture… so they're a theoretical value rather than an actual value. The T-stop takes into account the number of elements in a lens's optical construction, the quality of the optics and the effectiveness of the anti-reflection coatings. So, for example, due to variations in…
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Camera (Digital) - 1 Issue, Issue 429