Aperture F-Stop Converter
Compare two f-numbers in your browser. T-stop output is an estimate based on your assumed lens transmission, never a measured lens specification.
A QUICK WALKTHROUGH
How to use this tool
- Enter two f-numbers such as f/2.8 or 2.8.
- Review the stop difference and relative light ratio.
- Optionally enable the clearly labelled transmission-based T-stop estimate.
Formula
Stop difference = 2 × log2(B / A). Light ratio from A to B = (B / A)². The wider, smaller f-number is treated as the light reference.
T-stop boundary
Estimated T = f-number / √T, where T is the assumed transmission fraction. This is a rough assumption-based estimate, not a lens measurement; actual T-stop depends on the specific lens.
GOOD TO KNOW
Common questions
Can this give an exact T-stop?
No. It only estimates T-stop from the f-number and an assumed transmission percentage. Use a manufacturer specification or bench measurement for a real lens.