What Does Focal Length Mean In Cameras
Many photographers misunderstand the concept of focal length. Reverse to what some people recall, the focal length of a lens is not the lens's physical dimension and it has lilliputian to do with its overall size. And so, what is information technology and so? In this article, I will respond that question and discuss how to determine which focal length is right for your style of photography.
Definition of Focal Length
Without getting into an in-depth physics discussion, the focal length of a lens is an optical property of the lens. It measures the distance, in millimetres, betwixt the optical heart of the lens and the photographic camera'southward sensor (or pic plane). It is determined with the photographic camera focused to infinity. Lenses are named by their focal length, and yous can find this information on the barrel of the lens. For example, a 50 mm lens has a focal length of 50 mm.
In the definition of focal length, I mentioned the "optical centre" of a lens. You lot may be wondering what this is. Well, a camera's lens is not made from a unmarried slice of glass. Instead, it is a combination of lens elements and groups of elements. These combinations aid to focus the calorie-free and cutting down on distortions. The location where all the calorie-free rays converge to form a sharp image is known equally the optical centre of the lens.
Focal length is a property of the lens itself, non the photographic camera. What I mean past this is that a fifty mm lens is a 50 mm lens, regardless of whether on a full frame, cropped sensor, or medium format photographic camera. However, the size of the sensor does play a office in the lens/photographic camera combination's field of view, but more about this in a infinitesimal.
The Important Stuff
While the definition of focal length may exist relevant to some people, as photographers, it is non something you need to recall. What is more important to understand is what focal length tells us. Focal length describes the angle of view of a lens. That is, how much of a scene before us the lens captures. And in add-on, how large subjects within the frame appear. The longer the focal length of a lens, the narrower its bending of view. Subjects announced larger using long focal length lenses than they do viewing them with our eyes. On the other hand, lenses with short focal lengths take in a much wider angle of view. Thus, elements seem much smaller in the frame than they do to our eye.
Take a wait at this illustrative sketch. According to Nikon, its 500 mm f/five.six lens has an bending of view of 5o, while its 50 mm f/i.4 lens has an angle of view of 46o. And lastly, its 20 mm f/1.8 lens has an angle of view of 94o. As y'all can see, the longer 500 mm lens takes in a much thinner slice of the scene. As a upshot, merely a portion of a unmarried gunkhole is captured in the shot. On the other mitt, the l mm lens has a wider bending of view. Standing in the same location, you can capture a much broader department of the scene, including several boats and more of the distant rocks. Withal, with the twenty mm lens, you can capture the entire scene in a single frame.
On a recent trip to Lake Tahoe, I came beyond 2 fellows rock climbing while I was hiking. Although I did not have my photographic camera on a tripod, I was sitting down on the rocks and captured all 4 shots from the same spot. Find how my images narrow in on the scene as I zoom in on the climber. At a 25 mm focal length, y'all tin can barely spot the men. Alternatively, at 140 mm y'all can see the expression on the climber's face up. Incidentally, he managed to climb some other iii m up the face earlier he lost his grip, slipped off the rocks, and repelled safely back down to the basis!
Field of View and Equivalent Focal Length
The terms "bending of view" and "field of view" frequently get used interchangeably. Nonetheless, as I said higher up, the bending of view is an optical property of the lens. It does not change regardless of what type of camera is existence used. Field of view, on the other hand, is a outcome of the lens/camera combination. Field of view non just depends on the focal length of the lens merely as well the camera'south sensor size.
A total frame camera has a sensor that is the same size equally a 35 mm picture show negative (36 mm x 24 mm). However, digital cameras today come up with a broad variety of sensor sizes depending on the manufacturer and camera model. Sensors that are smaller than full frame are considered cropped sensors. This term comes about from the fact that these smaller sensors see less of a scene, in a like manner to what cropping an image does.
The phrase "effective focal length" (also known as equivalent 35 mm focal length) is used to equate what a lens captures in 35 mm sensor terms. Because most people are used to working with 35 mm film cameras, at to the lowest degree those of u.s.a. with a few grey hairs, the total frame format was adopted as the standard. Equivalent focal length describes the focal length of a lens y'all would need to put on a full frame photographic camera to capture the same field of view as a given lens on a cropped sensor camera. This is where crop factors come into play. The equivalent focal length is found by multiply the focal length of the lens by the non-full frame camera'southward crop factor. For Nikon, it's DX cameras have a crop factor of one.5. Canon's EF-S cameras take crop factors of 1.6. Additionally, micro four-thirds cameras have a crop cistron of two.0, and Sony and Panasonic'due south ane″ sensors take a crop gene of ii.vii.
This image below was taken with a 24-70 mm f/ii.8 lens at 44 mm on my total frame Nikon D800. If I had put this exact lens, at the aforementioned zoom, on my Nikon D500 (cropped sensor), it would still be a 24-seventy mm lens at 44 mm. However, the reduced field of view – due to the cropped sensor camera – would not see the same surface area. In this situation, I would just capture what is outlined in red. My effective focal length on the D500 would be 44 mm x ane.5 or 66 mm. In other words, if I wanted to capture what is outlined in crimson on my D800, I would take to put on a lens with a 66 mm focal length. Of course, I could besides zoom my 24-70 mm lens from 44 to 66 mm.
Nasim wrote an excellent article on Equivalent Focal Length and Field of View a few years back. For a much more detailed caption, check his article out.
Classifications of Focal Lengths
Camera lenses are classified into 5 descriptive categories depending on their equivalent focal length. Ultra broad-bending lenses accept a focal length of less than 24 mm in full frame terms. They capture incredibly broad views. Notwithstanding, because of this, they often present a distorted view of the globe. They are fun lenses to use and accept a very close minimum focusing distance and a large depth of field. If you lot photograph interiors, these lenses are well worth having in your bag.
Wide bending lenses have an equivalent focal length in the range of 24 mm to 35 mm. These lenses yet have in a wide view and are oftentimes used by landscape and architectural photographers. When you use a wide lens, it is a good idea to try and include some foreground involvement. This volition give your photos a sense of scale and help to pb viewers into your paradigm. Because these lenses have very large depths of field, it is easy to become both about and far objects in sharp focus.
Standard lenses have focal lengths between 35 mm and 70 mm. They capture the world in a manner very like to how our optics see. They cause minimal baloney, and then are a favourite of portrait photographers. Another feature of lenses in this focal range is their power to isolate a discipline from its background using much shallower depths of field than wide angle lenses.
The focal lengths betwixt seventy mm and 300 mm are considered telephoto lenses. They are regularly used by wild animals photographers to become closer to their subjects without being seen. These lenses have shallow depths of field, fifty-fifty at small apertures, so acquiring abrupt focus is critical.
Super telephoto lenses have focal lengths exceeding 300 mm. They are often used for photographing birds and other minor afar subjects. These lenses tin be very large and heavy and may crave the use of a tripod to support them. They are also very expensive! Nikon'south AF-S NIKKOR 800mm f/five.6E FL ED VR lens is a whopping $xvi,300 at the time of writing this commodity! Luckily there are some much cheaper options available now that allow photographers with normal pocketbooks to become into bird photography!
Again, all the numbers I simply mentioned are in full-frame terms. If you accept a crop-sensor camera, y'all will need to find your equivalent focal lengths by dividing these numbers by 1.5, 2, or whatever your crop factor is.
Zooms vs Prime number?
Prime number lenses have a single, fixed focal length. A zoom lens, on the other hand, has a variable focal length. Some popular zoom lens ranges include 16-35 mm, 24-seventy mm, and 70-200 mm. A great lens for travelling is one that covers both the wide and telephoto ranges, such as an eighteen-200 mm lens. The reward hither is that you lot will not have to carry a multitude of lenses with you, or change lenses to shoot wide vistas and close-ups of architectural details.
In that location is a downside to zooms, though: they are often not as optically precipitous as primes. Although this gap is endmost with newer and amend technology, it withal exists, specially when dealing with superzooms like xviii-200 mm lenses. Another drawback is that they tend to take narrower maximum apertures than prime lenses. While a top of the line zoom might take a fixed discontinuity of f/ii.8, primes in a similar focal length may open up much wider and often permit in several more stops of light. This can make prime lenses more than desirable in low low-cal conditions. For more data on primes versus zooms, see our larger article on the subject.
Conclusion
Don't get hung upwardly on the definition of focal length, or even the difference betwixt the bending of view, the field of view, and the equivalent focal length of a lens. What is of import to remember is that lenses with long focal lengths bring objects closer, like a telescope. And, on the flip side, wide angle lenses are bang-up for capturing big vistas. If y'all demand to get closer to your subject than y'all tin can physically, opt for a telephoto lens. If landscape and architecture are genres you enjoy shooting, then brand sure you comport a broad angle lens. For portraiture, and anything else in between, you can't go incorrect with a nifty-fifty in your bag.
If you lot have questions, delight drop me a line in the comments below, and thanks for reading!
Source: https://photographylife.com/what-is-focal-length-in-photography
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