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Focal Length Explained

This information is an extension to the LEARN article in the Winter 2020 Newsletter. If you are starting here, do go and check out the newsletter, too. 

Many photographers do not use the full creative potential of their lenses. And many don’t realize what the controls of the lens are. I believe that one thing that contributes to this confusion is that the lens adjustments are accessed through the camera body. This creates a disconnect. For instance, to auto-focus you press slightly on your shutter button on the camera body, and to change your aperture you adjust your f-stop selection with your main control wheel also on the camera body, while all along these mechanisms are actually in the lens.

All lenses have 3 controls; aperture, focus, and focal length. Each of these controls offer the photographer different options in how they record their scene. They are the creative controls of the lens. The following information only addresses the focal length as I find that it is often misused or underused for creativity.

Focal length – In technical terms the focal length number, in millimeters, is determined by the distance between the point in the lens where the light-rays converge and the point at which the light reaches the digital sensor or film while focused at infinity.

It is not the actual length, or size, of the lens barrel. The focal length number is the basic description of the lens and how we usually refer to it. We also talk about lenses in regard to their angle of view which also relates to the focal length.

 

 

Wide Angle gives, just as it implies, a wider angle of view. And in doing so, it makes all the objects in your scene smaller than how they look to the naked eye. There are many applications for using wide-angle lens. Two good basic ones are for shooting indoors and landscapes.

 

Telephoto lenses have a narrow angle of view, and as the name implies, it magnifies like a telescope, or optically brings objects closer to you. This, like the wide-angle lens, is distorting reality by making the objects different from how the eye sees them. Telephoto lenses are often used when you can’t get close to your subject, like a sports game or wildlife.

 

The normal lens is the only lens that will record the objects truly as the eye sees the scene. The objects will be accurate in their relative size and in their relation to their distance to each other. But the angle of view is not how the eye sees.

 

In the above 3 images I stood in one place and simple used the three options on my lens to illustrate angle of view and background-foreground relationship. 

Fisheye Lens – The only lens that comes close to matching the angle of view of the human eyesight, which is basically 180°, is a fisheye lens. A fisheye lens is an extreme wide-angle lens that will drastically distort your image and give you a circular rather than rectilinear image.

Fisheye Lens, Rockport Harbor

 

Fixed or Prime Lenses – When a lens has one focal length number (ex: 28mm) it is a fixed focal length lens, also known as a prime lens. These lenses could either be a wide angle, normal, or telephoto lens.

 Zoom Lens – If the lens has a range of numbers (ex: 18mm-55mm), it is not a fixed or prime lens, it is a zoom lens that has a range of focal lengths in one lens and the numbers represent the minimum and maximum focal lengths of that lens. In the above example it has a wide-angle range, the normal position, and a telephoto range in one lens. Not all zoom lenses have this. Some are only wide-angle zoom lenses in that they don’t even reach the normal position (ex:10mm-22mm) or only telephoto zoom lenses (ex:70mm-300mm).

Wide Angle Fixed Lens
18mm-55mm Zoom Lens

 

 

 

 

 

 

 

What’s important about the focal length numbers, is that you understand that the lower, or smaller, numbers are wide-angle lenses and the objects will look smaller. We also refer to these as short lenses. (15mm, 18mm, 24mm)

I had to move in very close to the shed to get the same framing as the next image.

Wide Angle

  • Short lens
  • Small focal length number
  • Small objects

 

 

 

The higher, or larger, numbers are telephoto lenses and they make the objects look larger. We refer to these as long lenses. (70mm, 105mm, 200mm, 300mm, etc.)

Notice how this telephoto lens brings the background closer to the shed.

Telephoto

  • Long lens
  • Large focal length number
  • Large objects

 

 

 

If you want your background to be less interactive with the foreground, use a wide angle lens. If you want the background to relate to the foreground, use a telephoto lens.

While there are many options for a wide-angle lens or a telephoto lens, as mentioned above, your normal lens is only one number. If you are shooting with an SLR camera then your normal lens is probably either a 35mm or a 50mm. It depends on your sensor size. Any number lower than your normal is wide-angle. Any number higher is a telephoto. Simple!

EXAMPLE: If you have a cropped sensor and you are using the “kit lens” (the one that comes with the camera when you buy it) and it is a zoom lens. The focal length numbers on this zoom ring will probably look something like this 18 – 24 – 35 – 55. The 35 is your normal, any position lower is wide-angle, any position higher is telephoto, and that even includes the areas between the numbers.

 

Point-n-Shoot Cameras

All of these cameras and others that have zoom lenses that are permanently attached to the camera are always in their most wide-angle position when you first turn the camera on. In order to find your normal position you have to zoom out slightly.

On Point-n-Shoot cameras you usually have a lever near the shutter button. Push it towards either side and it zooms in or out. There could be an indicator on either side that illustrates a rectangle with 1 or 3 trees in it. Towards the 1 tree is telephoto, towards the 3 trees is wide angle. Or you might just have a “W” and a “T” to indicate Wide and Telephoto.

Smart Phones & Tablets

Your phone or tablet has an extremely wide angle fixed lens. When you zoom in by spreading your fingers across the screen, you are actually just cropping the image in a similar way as if you had an image up on your computer and simply cropped down to the important part of the scene. Essentially, you are just throwing away areas of the image, and thereby, throwing away pixels. This is called a ‘digital zoom’, and you are losing resolution. Zooming on a phone or tablet is not a function of the lens.

To gain a better understanding for your lenses, try doing the exercises that are illustrated here and in the Winter 2020 Newsletter.

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