Understanding Lens Aperture Numbers

In this article we will try to understand the meaning of numbers in the lens aperture, and why the larger lens aperture (the smaller the f number) the more expensive the price of a lens?

Have you ever wondered, where the aperture unit is usually expressed in numbers like the f / 4, f/5.6 or f/22 (or too f4, f5.6 or f22) come from? and why the greater diameter of the lens and the lens the smaller physical size of the figure?

Photo above shows the physical size comparison between the Nikon 50mm f/1.8G lens and 50mm f/1.4. Aperture scale figures stated above comes from the comparison between the lens and the focal length of the lens diameter:

For example, if we had a 50mm lens and an optical diameter of the front lens is 25mm, then we have a lens f / 2 (or also often expressed as f2)

aperture = 50:25 = 2

If the focal length of a 50mm lens and a 50mm lens diameter, meaning the lens maximum aperture is f / 1. In figure f / 1, the diameter of the lens is 2 times larger than f / 2, and there are 2 stop difference between f / 1 and f / 2. And lens f / 1 can be passed 4 times more light than the lens f / 2 aperture so that the greater the faster and more good use in low light conditions.

It also helps explain why there is a big difference in the way the price of the lens focal length is the same but different maximum aperture. For example, try to compare the Canon 85mm f/1.2 lens and Canon 85mm f/1.8. Canon 85mm f/1.2L lens sold at prices above USD 20,000 while the 85mm f/1.8 lens costs about USD 40,000. If we return again from the formula above, then to produce a 85mm lens with f/1.8 aperture, with a 47mm diameter lens enough (85/1.8 = 47.2). While to get the f/1.2 aperture, 85mm lens diameter had to be about 70 mm, almost twice as big is not it? The more material, the more optical and made ​​it harder = more expensive.


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