f-Stop Calculator
Calculate f‑stop (aperture number) from focal length and aperture diameter, or find diameter from f‑stop. Also compare exposure stops.
Find f‑stop (N)
Find Aperture Diameter (D)
Exposure Change (stops)
mm
cm
mm
cm
f‑stop N = f / D. Example: 50mm / 25mm = f/2.
Common Lenses
Presets set focal length and f‑stop. Adjust as needed.
f‑stop (N)
f/2.0
N = f / D
Wide
Medium
Narrow
f/1.4 f/4 f/11 f/22
Formula Used
N = f / D
Equivalent Stops
-
Depth of Field
-
Photography Formulas
N = f / D
ΔEV = log₂(N₂² / N₁²)
N: f‑stop (aperture number)
f: focal length (mm, cm)
D: aperture diameter (same unit as f)
ΔEV: exposure change in stops (positive = darker)
Common stops: f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22
Each stop halves/doubles the light area.
People Also Ask
🤔 What is f‑stop in photography?
f‑stop (f‑number) = focal length ÷ aperture diameter. It controls how much light enters the camera. Smaller f‑number = wider aperture = more light.
🔍 How do I calculate exposure change when changing f‑stop?
Exposure change in stops = 2 × log₂(N₂/N₁). Each full stop (e.g., f/2.8 to f/4) halves the light.
⚡ Why are f‑stops numbered like 1.4, 2, 2.8, 4, 5.6…?
Each stop multiplies the previous by √2 ≈1.414. Because area is proportional to (1/N)², halving area needs N multiplied by √2.
📏 How does f‑stop affect depth of field?
Smaller f‑number (wider aperture) gives shallower depth of field (blurry background). Larger f‑number (narrow aperture) gives deeper focus.
🎯 What is the fastest lens ever made?
The fastest commercially available lens is the Carl Zeiss Planar 50mm f/0.7, used in NASA missions. Very few exist.
🔥 Real‑world applications of f‑stop?
Portrait photography (wide aperture for bokeh), landscape (narrow for deep focus), low‑light shooting (wide aperture), and controlling exposure.
What is f‑stop?
f‑stop (also called f‑number) is the ratio of the lens's focal length to the diameter of the entrance pupil (aperture). It is written as f/N, e.g., f/2.8 means focal length divided by 2.8 gives the aperture diameter.
Why f‑stops matter
- Exposure: A smaller f‑number lets in more light (faster shutter speed possible).
- Depth of field: Smaller f‑number = shallower depth of field (blurred background).
- Diffraction: Very small apertures (high f‑number) cause diffraction, reducing sharpness.
Standard f‑stop scale: f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32. Each step halves the light (one stop).
Common f‑stop Values & Light Ratios
| f‑stop | Relative Light (compared to f/1.4) | Stops from f/1.4 | Typical Use |
|---|---|---|---|
| f/1.4 | 1× | 0 | Very low light, shallow DOF |
| f/2 | ½× | 1 | Low light, portrait |
| f/2.8 | ¼× | 2 | General, zoom lenses |
| f/4 | ⅛× | 3 | Kit lenses, landscape |
| f/5.6 | 1/16× | 4 | Typical daylight |
| f/8 | 1/32× | 5 | Sharpest for many lenses |
| f/11 | 1/64× | 6 | Landscape, deep DOF |
| f/16 | 1/128× | 7 | Maximum DOF, diffraction starts |
| f/22 | 1/256× | 8 | Diffraction visible |
Common Questions
What does "f‑stop" stand for?
The "f" stands for focal length. So f/2 means the aperture diameter is focal length divided by 2.
How many stops between f/2.8 and f/8?
From f/2.8 → f/4 is 1 stop, f/4 → f/5.6 is another, f/5.6 → f/8 is another: total 3 stops. So f/8 lets in ⅛ the light of f/2.8.