Online Tool Store
Aperture F-Stop Converter
Compare two apertures to get the stop difference, light ratio, and an estimated T-stop — calculated live in your browser, no uploads.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
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Enter either as "f/2.8" or "2.8" — a smaller f-number always means more light.
- Aperture A
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- Aperture B
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How it works
- Enter two apertures to compare, as "f/2.8" or just "2.8" — either works.
- Choose whether to show the stop difference, the light ratio, or both.
- Read the stop difference, which is the number that matters for exposure compensation.
- Turn on the T-stop estimate and adjust the assumed transmission if you want a rough sense of real transmitted light — remember it is an estimate, not a measured spec.
Why a cut cannot always land where you asked
F-numbers follow a geometric series where each full stop halves the light, so the numbers go up by a factor of the square root of two.
[K] � � � � � � [K] � � � � � � [K]
f/1.4, f/2, f/2.8, f/4, f/5.6, f/8 are consecutive full stops — each admitting half the light of the one before.
FAQ
What is the difference between an f-stop and a T-stop?
An f-number is a geometric ratio of focal length to aperture diameter. A T-stop measures light actually transmitted, accounting for absorption in the glass. A T-stop is always a slightly higher number than the f-number of the same lens.
Why is the f-number sequence so odd?
Because each full stop halves the area of the opening, and area scales with the square of diameter. That gives a sequence multiplying by the square root of two, which produces 1.4, 2, 2.8, 4 rather than round numbers.
Does aperture affect anything besides exposure?
Depth of field and diffraction. Opening up reduces depth of field; stopping down past a lens's optimum softens the whole image through diffraction, usually somewhere around f/8 to f/11 on full frame.
Can this tool give me an exact T-stop for my lens?
No — T-stop is a measured property of a specific lens (its coatings, element count, and how much light they absorb), not something derivable from the f-number alone. The T-stop estimate here lets you enter an assumed transmission percentage and shows roughly where the T-stop lands, which is useful for a ballpark but not a substitute for a manufacturer or bench measurement.
What does the light ratio number mean?
It is how many times more light the wider aperture lets in compared with the narrower one. A 3-stop difference is an 8× ratio — f/2.8 lets in 8 times the light of f/8 at the same shutter speed and ISO.
How we compare
| Feature | Online Tool Store | split-video.com | VideoKit |
|---|---|---|---|
| Compare two apertures for stop difference | ✓ | ✓ | ✓ |
| Light ratio shown alongside the stop count | ✓ | ✓ | Stops only |
| T-stop estimate from an adjustable transmission | ✓ | ✗ | ✗ |
| Nothing to upload, no sign-up | ✓ | ✓ | ✓ |
Aperture F-Stop Converter gives the stop difference, which is the number you actually apply to shutter speed or ISO.