Back to Basics: What are those numbers on my lens?

Andrew Beck Andrew 4 Comments

Given how many people would have either been given or bought themselves a camera over the festive season I thought it would be a great idea to run a “Back to basics” series of posts on the blog.

In this first post I’d like to look at, as a recent guest so eloquently put it, “those numbers on my lens”.

Focal Length

The first set of numbers mentioned in the lens specifications refers to the focal length of your lens and is represented in millimetres. These have nothing to do with the actual size of the lens but rather how much zoom you have. Very technical I know but remember, we are going back to basics here.

Smaller numbers yield a wider field of view as can be seen with the Canon 16-35mm lens

Canon 16-35mm Lens at 35mm

Larger numbers, such as those offered by the Canon 100-400mm yield a narrower field of view and allow you to get in closer to your subject.

Canon 100-400mm lens @ 400mm

The first number represents the widest possible field of view (minimum focal length), whilst the second number represents the narrowest field of view or maximum zoom (greatest focal length).

Not all lenses have the ability to change focal lengths e(eg from 16 to 35mm or 100-400mm) and are referred to as prime lenses as they operate at a fixed focal length (eg 50mm, 300mm, 400mm).

Generally speaking, the field of view of the human eye is equivalent to 50mm and anything smaller than 35mm would be considered a wide angle lens whilst anything with a focal length greater than 85mm is a telephoto lens.

Aperture Range

The second set of numbers represented as something along the lines of ” 1:3.5-56″ or “1: 2.8” refers to the aperture range of the lens.

In the example above, the focal length of the lens is clearly marked as 80-400mm.

This if followed by “1:4.5-5.6”.

These maximum aperture values are linked to the foal length values and in essence can be read as follows:

“When I am at a focal length of 80mm my maximum aperture will be F 4.5, however, when I zoom in to 400mm my maximum aperture value drops to F5.6”

Not all lenses are created equal though, some have a fixed maximum aperture throughout the range of the focal length. The canon 70-200mm F2.8 and 16-35 mm F2.8 lenses are great examples of this.

The specifications of “70-2mm 1: 2.8” can be read as follows:

“Regardless of whether I am at a focal length of 70mm or 200mm, my maximum aperture value will still be F2.8”

This brings us to the next question, and the next post in the series: What is Aperture and how can I use it in my photography?

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About the Author

Andrew Beck

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Very few people can tell you what their passion in life is. Even fewer will be able to tell you that what they do for a living is in fact their passion. My love for the bush and conservation took me on journey which would not only allow me to explore the continent which fascinates me so much, but to share my passion for photography and conservation with others. Be sure to check out my my website and instagram account.

Comments 4

  1. Pingback: Back to Basics: What are those numbers on my lens? - Africa Freak

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  4. Anne-Marie Hiscock

    Hi there, thank you for your email, please can you confirm what the cost is for subscribing to your “Back to Basics Online Course”

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