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What Is Focal Length?
Focal length is the measurement of distance (in millimeters) between the point of convergence of your lens and the sensor recording the image. Focal length is expressed by a number, and that number tells you how much of the scene your camera will be able to capture. Smaller numbers have a wider angle of view and show more of the scene; larger numbers have a narrower angle of view and show less.
How Does Focal Length Affect an Image?
There are multiple ways focal length impacts image:
- Field of view. The focal length determines how much of a scene is portrayed in an image. Smaller focal length lenses are called wide-angle lenses because they have a wider field of view. Lenses with a large focal length are called telephoto lenses and have a smaller field of view.
- Depth of field. Telephoto lenses also have a large depth of field, which means they can focus in on object that’s very far away.
- Perspective. The focal length changes the perspective and scale of your images. A Smaller focal length will give you a wider perspective and greater scale for your images. A larger focal length will narrow your perspective, zooming in on a tight shot on a smaller, more detailed scale.
- Image shake. Image shake is the blurriness and reduction in image quality that occurs from the vibration of pressing the shutter release down. When using a lens with a large focal length and tight perspective, the lens and camera become sensitive to the slightest motion. Image shake can occur if you are not using a tripod.
Two Primary Types of Camera Lenses
There are two main types of camera lenses.
- Prime lenses, or fixed lenses, have only one focal length available to them. “Fixed” means that the focal length of the lens does not and can not change. Prime lenses are easier to manufacture, and tend to be more inexpensive than zoom lenses.
- Zoom lenses have a range of focal lengths. Zoom lenses are more complex to build, since they contain multiple lenses that allow the photographer to adjust focal length, usually by twisting the grooved ridges on the outside of the lens. While they are more expensive, they are also more versatile; you would need two or three different prime lenses to get the range of focal lengths that you would get with a single zoom lens.
Focal Length Comparison in Camera Lenses
There is a wide variety of camera lenses, and therefore focal lengths, available to budding photographers. Certain lenses are better suited to certain types of photography; for example, ultra-wide angles are great for landscape photography whereas telephotos are a better option for wildlife photography.
- Ultra wide angle: Focal length between 8mm and 24mm
These lenses are sometimes called fisheye lenses, which have a very wide viewing area. While they can take an image of up to 180 degrees around the lens, they distort the image quite significantly, making everything appear almost as if inside a sphere.
- Standard wide angle: Focal length between 24mm and 35mm
Smaller focal lengths and a wider angle can distort images. With a lens of this size, distortion is minimal and the image appears more natural. Pretty much everything is in focus unless your subject is very close to the camera and there is less spatial distortion than a very wide lens, but it still makes things seem farther away than they actually are.
- Standard lens: Focal length between 35mm and 70mm
These versatile lenses are good for just about any type of photography, from portraits to landscapes. These all-in-one lenses render images roughly the way the human eye sees the world., and easily adjust to a shallow or deep depth of field, depending on aperture.
- Telephoto: Focal lengths between 70mm and 300mm or more
These lenses are ideal for picking out a distant subject, the way a telescope does. Good for compressing your subject and the background, which makes the background appear much closer to the subject. These lenses quite often have a shallow depth of field unless everything you’re shooting is far away
How to Select a Camera Lens
Since different camera lenses produce different focal lengths, a good photographer tends to keep several options in their arsenal. Here are a few things to keep in mind when selecting a new lens:
- Check crop factor. The focal length of a lens is determined by using 35mm film, or with a standard 35mm camera sensor. Check your camera’s sensor size to make sure it’s in line with the standard; if not, the lens will present a slight skew towards telephoto (so, for example, if your camera has a crop factor of 1.5 and you opt for a 100mm lens, your image will actually capture at 150mm). Both Canon and Nikon produce cameras with smaller sensors.
- Understand your subject. Using a telephoto lens for portraits would be as awkward as trying to photograph a hippo from afar, using only a fixed ultra-wide angle. Make sure you’re clear on what you’re photographing before jumping in and purchasing a new lens. Check this handy guide on the best camera lenses for each situation and subject:
- Best Beginner Camera Lens. The 50mm is by far the most popular starter lens, as it strikes a nice balance between field of view and depth of field, and doesn’t require any tinkering with the focal lens to produce a crisp image.
- Best Lens for Travel Photography. Travel photography is unique in that you’ll want to travel light, but want to have the option of capturing a lot of detail. A standard zoom lens should provide you with enough flexibility to get each shot.
- Best Lens for Sports Photography. Telephoto zoom lenses are ideal for action-packed scenarios you’re going to witness from afar.
- Best Lens for Landscape Photography. Before heading out on an outdoor adventure, consider grabbing two lenses: a wide-angle (or ultra wide-angle) as well as a standard lens. With landscape photography, you want to have the flexibility to capture both scale and detail.
- Best Lens for Portrait Photography. Fixed, standard lens between 35mm and 70mm are great portrait lenses; the lack of zoom options ensures clarity of image (so no fuzzy or blurry faces).
- Best Lens for Macro Photography. A telephoto lens of at least 200mm is best for macro photography. This powerful lens can capture subtle details from afar.
- Best Lens for Architecture Photography. A standard wide angle lens features a decent field of view to capture most, if not all, of a building.
- Best Lens for Street Photography. As with portrait photography, street photography benefits from the unique, clear look that standard fixed lenses produce. If you want to get creative, however, opt for a standard zoom lens to play with your subject’s size in relation to the background.
- Best Lens for Wildlife Photography. Telephoto zoom lenses come in handy for potentially dangerous situations, or scenarios in which you want to capture a scene without disturbing the subjects. Wildlife can be unpredictable, and a telephoto lens helps ensure you can keep enough distance between yourself and the animals while still getting the shot.