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What Is Focal Length in Photography?

The idea of focal length is misunderstood by many photographers. Contrary to popular belief, the focal length of a lens is not the physical dimension of the lens and has little to do with the total size of the lens. Now tell me, what is it. Answering that question and discussing how to choose which focal length is best for your style of photography will be covered in this article.

Focal Length is defined as the distance between two points.

Without entering without delving into the complexities of physics, the focal length of a lens is an optical characteristic of the lens. It measures the distance between the optical center of the lens and the sensor of the camera in millimeters (or film plane). It is calculated by focusing the camera on infinity. Lenses are identified by their focal length, which may be found on the lens’s barrel. For example, a 50 mm lens has a focal length of 50 mm and is used for portrait photography.

I discussed the “optical center” of a lens while discussing the notion of focal length. You might be asking what this is all about. A camera’s lens, on the other hand, is not constructed from a single piece of glass. rather than a single lens element, it is composed of many lenses and groups of lens elements. These combinations aid in concentrating the light and reducing distortions. The optical center of the lens is defined as the point at which all of the light rays converge to create a crisp image on the sensor.

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Focal Length

In contrast to the camera, the focal length is a characteristic of the lens. To clarify, I mean that a 50 mm lens is simply that: a 50 mm lens, regardless of whether it is used with a full frame camera, a cropped sensor camera, or a medium format camera. Nevertheless, there is a relationship between sensor size and field of vision for lens/camera combinations, which we will discuss in more detail later.

The Most Important Information

While the concept of focal length may be important to certain individuals, it is not something that you as a photographer should be concerned with remembering. What is more essential to grasp is what the focal length informs us about the situation. The focal length of a lens specifies the angle of view that it provides. That is, how much of the scene in front of us is captured by the lens. In addition, the size of the subjects within the frame is taken into consideration. Generally speaking, the greater the focal length of a lens is, the smaller its field of view is. When viewing objects with long focal length lenses, they look larger than when viewing them with our eyes. Lenses with short focal lengths, on the other hand, cover a significantly larger area of the scene than longer lenses. The items in the frame appear to be considerably smaller than they appear to our eyes as a result.

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Focal Length

Please have a look at this illustration. As stated by Nikon, its 500-millimeter f/5.6 lens has a field of view of 5 degrees, while its 50-millimeter f/1.4 lens has a field of view of 46 degrees. Finally, the camera’s 20 mm f/1.8 lens offers a field of view of 94 degrees. As you can see, the longer 500 mm lens captures a significantly narrower slice of the image than the shorter 400 mm lens. Consequently, just a piece of a single boat is visible in the photograph. The 50 mm lens, on the other hand, provides a more expansive field of vision. You may catch a considerably larger portion of the picture from the same point, including numerous boats and more of the far cliffs, by remaining in the same spot. With the 20 mm lens, on the other hand, you may catch the entire scene in a single picture.

Equivalent Focal Length as well as Field of View

The phrases “angle of view” and “field of view” are frequently used interchangeably in the scientific community. However, as previously stated, the angle of view is an optical characteristic of the lens and cannot be changed. Whatever sort of camera is being utilized has no effect on this phenomenon. A camera’s field of vision, on the other hand, is determined by the lens and camera it is using. The field of vision is determined not only by the focal length of the lens, but also by the size of the camera’s sensor.

An image sensor in a full frame camera measures approximately the same in size as a 35 mm film negative (36 mm x 24 mm). Digital cameras, on the other hand, are available in a broad range of sensor sizes, which vary based on the brand and camera type. Cropped sensors are those that have a sensor size that is less than the entire frame size. These smaller sensors view less of a scene than larger sensors, which is comparable to how cropping a photograph reduces the amount of information received from a scene.

For 35 mm sensors, the term “effective focal length” (also known as equivalent 35 mm focal length) is used to describe the distance between the lens and the 35 mm sensor. Because the majority of us, or at least those of us with a few grey hairs, are accustomed to working with 35 mm film cameras, the full frame format was accepted as the industry standard. The term “equivalent focal length” refers to the focal length of a lens that would be required on a full frame camera in order to capture the same field of vision as a given lens on a cropped sensor camera. Crop variables come into play at this point in the process. Calculating the equivalent focal length is accomplished by multiplying the focal length of the lens by the crop factor of the non-full frame camera. Nikon’s DX cameras feature a crop factor of 1.5, which is the same as the industry standard. Cameras from Canon’s EF-S series have crop factors of 1.6. Also of note is that micro four-thirds cameras have a crop factor of 2.0, while Sony and Panasonic’s 1′′ sensors have a crop factor of 2.7, both of which are significant.

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This photograph was shot with a 24-70 mm f/2.8 lens at 44 mm on my Nikon D850 full frame digital camera. In the same zoom range, if I had used this same lens on my Nikon D500 (cropped sensor), the focal length would have still been a 24-70 mm lens at 44 mm. However, because of the cropped sensor camera’s decreased field of view, it would not be able to observe the same amount of ground. In this case, I would only capture the portions of the image that are highlighted in red. My effective focal length on the D500 would be 44 mm x 1.5, or 66 mm, depending on the lens I use. To put it another way, if I wanted to capture what is highlighted in red on my D800, I would need to use a lens with a focal length of 66 mm or longer. Of course, I could also use my 24-70 mm lens to zoom in and out between 44 and 66 mm.

Focal Lengths Are Divided Into Several Types

The equivalent focal length of a camera lens is divided into five descriptive categories, each of which has its own classification. In full frame terminology, ultra wide-angle lenses have a focal length of less than 24 mm. Stunningly diverse perspectives are captured. In exchange for their skewed vision of the world, they frequently provide one. Because of their small minimum focusing distance and wide depth of field, they are a lot of fun to photograph with. When it comes to interior photography, these lenses are essential to have in your backpack.

In terms of equivalent focal length, wide angle lenses have equivalent focal lengths ranging from 24 mm to 35 mm. They nevertheless provide a wide field of vision and are frequently employed by photographers working in the landscape and architectural lenses. Try to add some foreground interest while photographing with a wide lens wherever possible. This will help to give your photographs a feeling of size and will assist visitors in entering your image more effectively. The fact that these lenses have extremely broad depths of field makes it simple to obtain crisp focus on both close and distant objects.

Lenses with focal lengths between 35 mm and 70 mm are considered standard. When they capture the world, they do it in a manner that is extremely similar to how our eyes view things. Photographers who specialize in portraiture like them because they produce the least amount of distortion possible. The ability to separate a subject from its backdrop using significantly smaller depths of focus than wide angle lenses is another characteristic of lenses in this focal range.

Telephoto lenses are defined as having focal lengths between 70 mm and 300 mm. Wildlife photographers utilize them frequently to get closer to their subjects while remaining undetected. Even at modest apertures, these lenses have narrow depths of field, making it important to achieve crisp focus.

Super telephoto lenses have focal lengths that are more than 300 mm in diameter. They are frequently employed for the photography of birds and other small distant things. Due to the fact that these lenses may be rather large and heavy, it is often necessary to mount them on a tripod. They’re also prohibitively costly! When I was writing this post, Nikon’s AF-S NIKKOR 800mm f/5.6E FL ED VR lens was priced at a staggering $16,300. There are several lots more affordable choices available now that allow photographers with typical budgets to get started in bird photography as well.

Every one of the figures I just gave is in terms of a full-frame frame of reference. If you use a crop-sensor camera, you will need to calculate your equivalent focal lengths by multiplying these values by 1.5, 2, or whatever your crop factor is.

What is the difference between zooms and primes?

Prime lenses feature a single focal length that cannot be changed. A zoom lens, on the other hand, has a focal length that can be adjusted. Zoom lenses with focal lengths ranging from 16-35 mm, 24-70 mm, and 70-200 mm are among the most common. A lens that can be used for both wide-angle and telephoto shots, such as an 18-200 mm lens, is ideal for traveling with your camera. With this method, you will not have to bring along as many lenses as you would otherwise, nor will you have to switch lenses between shooting wide views and close-ups of architectural features.

There is a disadvantage to zoom lenses, however: they are not always as optically crisp as prime lenses. Despite the fact that newer and better technology is narrowing the gap, it still persists, particularly when it comes to superzoom lenses such as the 18-200 mm zoom lens. Another disadvantage is that they have narrower maximum apertures than prime lenses, which is a disadvantage. While a top-of-the-line zoom lens could have a fixed aperture of f/2.8, prime lenses with a comparable focal length may open up much wider and allow in several more stops of light, according to the manufacturer. Prime lenses may be more attractive in low-light situations as a result of this. For additional detail on the differences between primes and zooms, please visit our more in-depth page on the subject.

Conclusion

Keep your attention away from the definition of focal length or even the distinction between an angle of view, a field-of-view, and the equivalent focal length of a lens. One thing to keep in mind is that lenses with long focal lengths, such as a telescope, bring distant things closer to the viewer. Wide angle lenses, on the other hand, are excellent for capturing expansive landscapes and views. If you need to go closer to your subject than you can physically get to it, a telephoto lens is the best choice for you. Consider carrying a wide-angle lens if landscape and architecture photography are among your favorite genres to photograph. You can’t go wrong with a nifty-fifty in your bag for portraiture, and it’s perfect for anything else in between.

Any questions or comments are welcome in the comments section below. Thank you for taking the time to read this article!

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