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Calculate aperture diameter, relative light transmission, and understand f-stop relationships
Aperture Diameter
17.86mm
At 50mm focal length
Relative Light
12.76%
Compared to f/1.0
| F-stop | Diameter (mm) | Relative Light | Stops from f/1.0 |
|---|---|---|---|
| f/1 | 50.0mm | 100.00% | 0 stops |
| f/1.4 | 35.7mm | 50.00% | 1 stop |
| f/2 | 25.0mm | 25.00% | 2 stops |
| f/2.8 | 17.9mm | 12.50% | 3 stops |
| f/4 | 12.5mm | 6.25% | 4 stops |
| f/5.6 | 8.9mm | 3.13% | 5 stops |
| f/8 | 6.3mm | 1.56% | 6 stops |
| f/11 | 4.5mm | 0.78% | 7 stops |
| f/16 | 3.1mm | 0.39% | 8 stops |
| f/22 | 2.3mm | 0.20% | 9 stops |
Aperture is one of the three pillars of photography exposure (along with shutter speed and ISO). Understanding how f-stops work is essential for controlling depth of field and exposure.
An f-stop (or f-number) is the ratio of the lens focal length to the diameter of the entrance pupil (aperture). It's expressed as f/N, where N is the f-stop number. A lower number means a larger aperture opening and more light entering the camera.
The standard f-stop scale follows a geometric progression where each full stop either doubles or halves the amount of light. The sequence is: f/1.0, f/1.4, f/2.0, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, and so on. Each step in this sequence represents exactly one stop of light.
The amount of light transmitted through a lens is inversely proportional to the square of the f-number. This means f/2.8 lets in exactly 4 times more light than f/5.6, because (5.6/2.8)² = 4. Understanding this relationship helps you quickly calculate exposure adjustments.
Because the f-stop is a ratio (focal length divided by aperture diameter), a smaller number indicates a larger aperture opening. Think of it like a fraction: 1/2 is larger than 1/8.
Most lenses perform best optically when stopped down 1-2 stops from their maximum aperture. For an f/2.8 lens, this would be around f/4 to f/5.6, where you get optimal sharpness and reduced aberrations while maintaining reasonable light transmission.
More aperture blades generally create smoother, more circular bokeh. Modern lenses typically have 7-9 blades. Lenses with 9 or more rounded blades produce the most pleasing out-of-focus areas, especially important for portrait photography.
Diffraction is the softening of images that occurs when using very small apertures (f/16 and smaller). Light waves bend around the aperture blades, reducing overall sharpness. This limits how small you can stop down before image quality degrades.
Indirectly, yes. Changing aperture affects the shutter speed needed for proper exposure. A larger aperture allows faster shutter speeds (reducing motion blur), while a smaller aperture requires slower shutter speeds (potentially introducing motion blur if handheld).