what is focal length

Here is a diagram to help you understand what is focal length. An understanding of focal length and zoom range will help you when you are considering buying a camera or a lens.

In layman's terms, the definition of a focal length is the distance from the center of the lens to the focused image on the sensor. A longer length would mean that it is more of a telephoto lens. A shorter length means it's more of a wide angle lens.

diagram of lens focal lengthNormal Focal Length Lens

In the diagram below, if you can imagine a longer lens (the space marked in red) with would give you a narrower angle of view of the subject. In other words a smaller amount of the subject would be focused on the sensor. Longer focal lengths are good for shooting sports, wildlife, and portraits of individual people.

Diagram of long focal length lensLong Focal Length Lens

A shorter lens would give you the wider view of a wide angle lens. Shorter focal length lenses are great for shooting landscapes, architecture, groups of people, and inside photos where space is limited.

Most cameras come with a zoom lens, which means you can essentially change the focal length of the lens. Zooming in narrows you angle of view and brings your subject closer. Zooming out widens the camera's view, includes more things in your viewfinder and make them smaller.

The chart below is for a full frame or 35mm size sensors. Point and shoot cameras have smaller sensors and so the actual distances in "mm" millimeters is smaller. Usually the camera maker will give you the equivalent numbers for the zoom.

chart of different focal lengths

Here is a basic chart of a few typical zoom lenses and their range of focal lengths.  The numbers in this chart are for a camera with a full-frame sensor.  With smaller DSLRs and point and shoot cameras, the actual mm numbers will be smaller, but the equivalents can easily be calculated using the crop factor number which is one of the specs of the camera.

The actual numbers are not as important as knowing the best lens or zoom setting to use in certain photographic situations.  These are the "common uses" in the chart below.

Cahrt of sizes and uses fro different focal length lenses

If it says it has a 4x zoom, it's range may be the 35mm equivalent of 25-100mm zoom. A 10x range might mean a 28-280mm zoom range of magnification.

why focal length matters

Focal length is important for several reasons. This is what really matters over anything else you read about focal length numbers.

  1. It affects how much of the scene you've included in your photo. You get to control exactly what you want included within your frame.
  2. You can change your perspective, the relative distance you are from the subject, and the relationships of different subjects within your photo. Wide angle lens setting exaggerate perspective. Long focal lengths "flattens" perspective.
  3. Focal length affects the depth of field. Used along with your aperture setting, focal length affects the range of things within your photo that are in sharp focus. Long telephoto focal lengths give you shallow depth of field. Short, wide angle focal lengths give you deep depth of field.

Another article that might deepen your understanding of what focal length numbers mean is here: Camera Lens Comparison.  I included sample photos showing 4 different focal length settings while using a Canon 5d, a DSLR with a full-frame sensor.

These are not strict guidelines to follow, just typical uses for certain lens types. If you have any questions, feel free to ask and I'll write an article when I get a chance.

What is a Prime Lens. A zoom lens gives you many focal lengths to choose from while having to use only one lens. What is a prime lens and why would anyone want to use one .Have fun as you discover more digital photography tips on this site.

Keep shooting. Keep learning. Keep improving.

Bruce Lovelace signature

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