How are stops between two apertures calculated?

Stops = 2 × log2(a / b), because light scales with the inverse square of the f-number. Opening from f/8 to f/4 is +2 stops and lets in four times the light.

What are the standard full f-stops?

The full-stop series is f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22 and f/32 — each step halves or doubles the light.

Does a smaller f-number mean more or less light?

A smaller f-number means a wider aperture and more light. f/2 lets in far more light than f/16, which is why low f-numbers are described as "fast" lenses.

How do I compensate one stop of aperture with shutter speed?

Each stop of aperture equals one stop of shutter speed or ISO. If you close the aperture by one stop (half the light), double the exposure time or double the ISO to keep the same exposure.

Why does light change with the square of the f-number?

The f-number is the focal length divided by the aperture diameter, so it controls the diameter of the opening. Light passing through scales with area, which is proportional to diameter squared — hence the inverse-square relationship.

What is a half-stop or third-stop?

Modern cameras let you adjust aperture in 1/2 or 1/3 stop increments for finer exposure control. A third-stop changes the light by a factor of about 1.26 (2^(1/3)) rather than 2.

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F-Stop Calculator — Gera Tools

F-stop calculator

How much brighter is f/2.8 than f/8? Photographers reach for an f-stop calculator whenever they change aperture and need to keep the exposure balanced — for example, opening up to blur a background, then compensating with shutter speed or ISO. Enter your starting aperture and your target aperture and this tool reports the difference in stops and the exact light-change factor between them.

How it works

The f-number is the ratio of focal length to aperture diameter, so light admitted scales with the inverse square of the f-number. The tool computes the stops between two apertures a and b as:

stops = 2 × log₂(a / b)

It then expresses the brightness change as a multiplier, 2^|stops|. A positive result means you are opening up (a smaller f-number, more light); a negative result means you are stopping down (less light). Each full stop doubles or halves the light.

Example

Going from f/8 to f/4: stops = 2 × log₂(8 / 4) = 2 × log₂(2) = +2 stops. The light factor is 2² = 4×, so f/4 delivers four times as much light as f/8. To hold the same exposure you would shorten the shutter speed by two stops (for instance 1/60 s → 1/250 s) or drop ISO by two stops.

Aperture change	Stops	Light factor
f/2.8 → f/2	+1	2× more
f/4 → f/8	−2	4× less
f/5.6 → f/2.8	+2	4× more
f/16 → f/4	+4	16× more

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