Why do we need to add 'equivalence' to the focal length and aperture of mobile phones?

Several recent articles have been recommended by the platform and have successfully added many new subscriptions. At the same time, some netizens also expressed confusion (and bad comments) about the concept of “equivalent aperture”. As I said before, the concept of "equivalent aperture" should be discussed at most once a year, so let's use this year's quota today.

Focal length classification of 50mm lens

On cameras with different formats, the focal length of 50mm lens is classified as follows:

1. Full-frame camera: standard lens
2. 4/3-frame camera: telephoto lens
3. Portable camera/mobile phone : Super telephoto lens
4. Medium format/large format camera: Wide-angle or ultra-wide-angle lens

Calculation of equivalent focal length and aperture

Equivalent focal length and aperture need to consider the frame factor.

• Equivalent focal length: Convert the focal lengths of different frames into focal lengths based on 35mm full frame.
• Equivalent aperture: Convert apertures of different frames to apertures based on full frame.

Calculation method:

• Equivalent focal length = lens focal length × equivalent coefficient (depending on the frame)
• Equivalent aperture = lens aperture × equivalent coefficient

Influence of frame

Frame size affects focal length and aperture Categories:

• Focal Length: Smaller formats require smaller focal lengths to get the same angle of view.
• Aperture: A smaller frame requires a larger aperture to achieve the same blurring effect.

The concept of equivalent

• Equivalent focal length: Provides comparison of viewing angles under different frames.
• Equivalent aperture: Provides comparison of blur and low light performance under different frame sizes.

Note:

• The physical clear aperture of the lens will not change.
• Cropping the image cannot change the focal length and aperture of the lens.

  

  Always remember, aperture = focal length ÷ clear aperture. When a lens is designed and produced, its maximum clear aperture is determined. If you want to multiply the focal length by an equivalent coefficient, you must also multiply the aperture by an equivalent coefficient, so that the equation can be maintained.

There is no such thing as making money without losing money. One side became longer and the other side became thinner.

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