Smartphone Camera: Aperture & F Number are more important than Megapixels

The smartphone camera aperture – not the sensor size or the thing called MP – controls much of your photo’s sharpness, exposure, brightness and focus. Here is why. The f-value is the ratio of the camera’s focal length to the diameter of aperture opening. So the focal length of a camera is another factor to consider when weighing in on the image quality of your smartphone camera. 

Read also Forget about megapixels, your smartphone’s sensor quality is what matters

For comparison, I listed below some high-end smartphones along with their corresponding focal length and aperture:

  • Samsung Galaxy S7/S7 Edge: 26mm, f/1.7 (INR 41000 +)
  • Apple iPhone 7/7+: 28mm, f/1.8 (INR 50000+)
  • Samsung Galaxy S6 Edge: 28mm, f/1.9 (INR 35000+)
  • Apple iPhone 6S: 29mm, f/2.2 (INR 37000)

The recently launched Oppo F3 Plus (INR 31000) and Moto G5 Plus (INR 17000) also have f/1.7 aperture which may be a competitive value add to these mid range devices. 

From this comparison, we can see that the Samsung Galaxy S7 gathers more light than the rest of the competitors. The size of the aperture opening is also responsible for the depth of field, which results in more or less bokeh: the isolation of the subject from the background. 

The f-number of an optical system such as a camera lens is the ratio of the system’s focal length to the diameter of the entrance pupil. It is a dimensionless number that is a quantitative measure of lens speed, and an important concept in photography. It is also known as the focal ratiof-ratiof-stop, or relative aperture. The f-number is commonly indicated using a hooked f with the format f/N, where N is the f-number.

A lens with a greater f-number projects darker images. The brightness of the projected image (illuminance) relative to the brightness of the scene in the lens’s field of view (luminance) decreases with the square of the f-number. 

Depth of field increases with f-number, as illustrated in the image here. This means that photographs taken with a low f-number (large aperture) will tend to have subjects at one distance in focus, with the rest of the image (nearer and farther elements) out of focus. This is frequently used for nature photography and portraiture because background blur (the aesthetic quality of which is known as ‘bokeh‘) can be aesthetically pleasing and puts the viewer’s focus on the main subject in the foreground.

Comparison of f/32 (top-left corner) and f/5 (bottom-right corner)

Shallow focus with a wide open lens

Image sharpness is related to f/number through two different optical effects: aberration, due to imperfect lens design, and diffraction which is due to the wave nature of light.The f-number of the human eye varies from about f/8.3 in a very brightly lit place to about f/2.1 in the dark. 

In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane.If an aperture is narrow, then highly collimated rays are admitted, resulting in a sharp focus at the image plane. 

A device called a diaphragm usually serves as the aperture stop, and controls the aperture. The diaphragm functions much like the iris of the eye – it controls the effective diameter of the lens opening. Reducing the aperture size increases the depth of field.

When it comes to photography, aperture and f number are more important than the mega pixels the companies advertise. Whatever the no. of pixels a camera boasts, image clarity depends mainly on aperture and f number completely.So the next time you choose which smartphone best suits your taste when it comes to photography, look at the full specs of the device and head directly to the f-value.


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