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Digital SLR Camera Basics

Maximum Aperture (Minimum f-number)

The maximum diameter of the lens opening is referred to as its maximum aperture or minimum f-number. The minimum f-number is the smallest f-number that can be selected with the lens. The maximum aperture varies from lens to lens and is included in the lens model name.

AF-S NIKKOR 50 mm f/1.4G
AF-S NIKKOR 50 mm f/1.4G
AF-S NIKKOR 24-70mm F2.8G ED
AF-S NIKKOR 24-70mm F2.8G ED
AF-S DX NIKKOR 18-55mm F3.5-5.6G VR
AF-S DX NIKKOR 18-55mm F3.5-5.6G VR

Examples

Lens name
Maximum aperture
Lettering on lens
AF-S NIKKOR 50mm F1.4G
F1.4
1:1.4
AF-S NIKKOR 24-70mm F2.8G ED
Fixed at f/2.8 regardless of focal length selected with lens
1:2.8
 
AF-S DX NIKKOR 18-55mm F3.5-5.6G VR
Varies with lens focal length, progressing from f/3.5 to f/5.6 as lens is zoomed in from 18 mm to 55 mm
1:3.5-5.6
 

Lens with small maximum aperture

AF-S DX NIKKOR 18-55mmF/3.5-5.6G VR

AF-S DX NIKKOR 18-55mm F3.5-5.6G VR

Lens with wide maximum aperture

AF-S NIKKOR 24-70mm F2.8G ED

AF-S NIKKOR 24-70mm F2.8G ED

The maximum aperture indicates the brightness of the image that the lens creates on the image sensor : lenses with wider maximum apertures (lower minimum f-numbers) create a brighter image on the image sensor than lenses with small maximum apertures (higher minimum f-numbers) . Lenses with wide maximum apertures are referred to as “fast” lenses because they create a brighter image on the image sensor, allowing faster shutter speeds. In some cases, a lens with a wide maximum aperture can be used for blur-free photography of subjects that might be blurred when photographed using a lens with a small maximum aperture. In addition, wider maximum apertures allow smaller depths of field that soften backgrounds, meaning the wider the maximum aperture the greater the softening effect and the more the subject appears to be separated from the background.

Maximum aperture and depth of field

Lens with small maximum aperture
Click image to enlarge.
Lens with wide maximum aperture
Click image to enlarge.

The same subject photographed with two lenses with the same focal length. Both photographs were taken at maximum aperture, the one on the left with a lens with a small maximum aperture and the one on the right with a lens with a wide maximum aperture, showing the softening effects of reduced depth of field.


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