Camera
T-Stop / F-Stop Converter
Convert between T-stops and f-stops with transmission loss.
Runs entirely in your browser. Nothing is uploaded.
How to use
- Set the f-stop marked on the lens.
- Set the transmission efficiency, how much light the glass actually passes.
- Read the true T-stop the lens meters at, plus the light lost in stops.
Examples
- A fast photo lens at f/1.4 with 90 percent transmission meters closer to T1.5.
- Cine lenses are marked in T-stops already, so two different lenses at the same T-stop expose identically.
- A complex zoom with more elements loses more light, so its T-stop sits further from its f-stop.
Frequently asked questions
What is the difference between f-stop and T-stop?
An f-stop is pure geometry, the aperture diameter against focal length. A T-stop measures the real light reaching the sensor after losses in the glass, so it is what you should meter by for consistent exposure.
Why do cine lenses use T-stops?
So that any two lenses set to the same T-stop expose the same, which keeps cuts matched across a set of lenses with different optical designs.
What transmission should I assume?
Most modern lenses pass 85 to 95 percent. If you do not know a lens, 90 percent is a fair estimate, which is roughly a sixth of a stop of loss.
