FOV to focallength

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Some lenses will feature two maximum apertures (shown as 1:4-5.6). This means that, as you zoom, the aperture capability changes. So at the shortest focal length, you may be able to shoot at f4, but once you zoom to the longest focal length, the widest aperture you’ll be able to shoot at will be f5.6. Generally lenses with wider apertures are favourable due to their increased light-capturing capabilities.

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Aperture refers to the opening in the lens that controls how much light reaches the sensor. This is indicated in the format 1:2.8, for example, with the second set of numbers indicating the maximum aperture.

focal length中文

Lenses focus the light onto the recording medium, which allows an image to be recorded. As you’ll see from the illustration of a DSLR camera below, light enters the lens and passes through the front element (2) before reaching several lens elements (3, 5 & 6).

But then consider the geekier side of it. what does the millimeter actually stand for. To put it simply, it stands for the distance between the back element of the lens and the camera’s sensor or film plane. With a zoom lens, you can expect that to change accordingly. With an option like a 24-105mm lens, the back element of the lens starts out at 24mm and as you zoom further into the subject (increased the millimeter numbers) you move the back element further away from the sensor and film plane. Part of this is why we call them “longer focal lengths” or “shorter focal lengths” because longer lenses need to be made, well, longer in order to accommodate the design.

Focallengthformula

Throughout this course, we’re referring to six essentials of photography. However, it is important to mention that this could in fact be five! Why? Because images can be recorded without a lens on so-called pinhole cameras (or camera obscuras).

Lenses with shorter focal lengths provide a much wider angle of view and less magnification. This makes them better suited to landscapes than to product photography.

Typically, lens names are formatted like this: Canon EF 24-70mm f/2.8L II USM Lens or Nikon AF-S 50mm f/1.8G. Each of these numbers and letters relays essential information, such as focal length, maximum aperture, lens version and focusing motor. Other features specified can include stabilisation, filter diameter and focusing distances.

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Essentially, the wider the field of view, the smaller in focal length number. The more narrow (telephoto) views are larger in focal length numbers. So, a 14mm lens will give you a wider field of view than an 85mm lens. But then things become even more confusing as pretty much every standard of focal lengths are then more or less based off of 35mm film.

You see, there are things called crop factors–and they are created in regards to how much smaller or larger a sensor or film plane is to 35mm film. So on a Four Thirds sized sensor, there is a 2x crop factor. So a 12mm lens will give you the equivalent field of view of a 24mm lens on a full frame 35mm camera. But nonetheless, the standard stays the same. The smaller the number of millimeters, the wider the field of view and focal length. The larger the number, the more narrow it is.

focal length是什么

Zoom lenses provide a variety of focal lengths. This makes them very versatile and reduces the need for multiple lenses.

Longer focal lengths offer a narrower angle of view and more magnification, which means they are better suited to sport or wildlife photography than architectural photography.

Depth offocus

Focal distance vs focallength

If you’re into photography, you most likely know the answer to the question “What do the letters ‘mm’ on a lens stand for?” But for the uninitiated and for lots of Americans who don’t know the metric system or what millimeters are, it can be pretty confusing. I mean, we can understand that eight inches is larger than two inches, right? So bigger, must mean better, right? No, not exactly and that couldn’t be further from the truth.

These elements serve to direct the light to a single focal point so that it can accurately be recorded by the sensor (9) once the mirror (7) flips up (triggered when you press the shutter button). Mirrorless cameras work the same way, but do not have the mirror or prism.

Prime (or fixed) lenses feature a fixed focal length. Available in a range of focal lengths, these lenses are known for delivering high-quality images. They also generally offer much wider apertures than zoom lenses do.

Some lenses feature a fixed aperture. Catadioptric, or mirror lenses, which used to be fairly common, usually feature a longer focal length, such as 500mm at a fixed aperture of f6.3. Most telescopes are catadioptric.

However, recording an image without a lens is far more complex, and doesn’t afford the photographer the same creative freedom. Essentially, without a lens, you're shooting at a very small fixed aperture. Thanks to the variations in magnification they offer, lenses allow us to shoot many different objects, which simply wouldn’t be possible with a camera obscura.

Focal length is usually indicated both on the side of the lens barrel and sometimes on the front of the lens, along with the lens diameter.