The first number after the brand name (measured in millimeters) is the focal length. This is not to be confused with focal distance. The focal length refers to the distance between your camera sensor (or film) and the “rear nodal point” of your lens. Defining a “rear nodal point” usually takes a master’s degree in optics and a couple of textbooks, so for our purposes, just think of it as your lens’ sweet spot.

Types ofcamera lensesand their uses

A camera lens works the same way, collecting and bending the light onto your digital sensor (or film, if you’re a time traveler from 1995). This is  why you never want to point your camera directly into the sun. It can fry your sensor — and possibly your eye, depending on the camera.

So far the calculation we have done above is about the horizontal FOV, however, often FOV should be considered in 3-dimension. Vertical FOV could be calculated given the Aspect Ratio of the senor, expressed in the equation below.

An average lens might have as many as six or seven elements in it. Thus, more expensive and complicated lenses may have as many as 15 to 20. Different-shaped elements can make for different effects, which is how you get specialized glass like macro, wide-angle, fisheye, apochromatic (“APO”) or telephoto lenses.

By varying the distance between the two lenses, you can change how much the light gets straightened. This changes the focus of the light and changes how blurry the picture is. That’s why when something is blurry, we call it “out of focus”.

Optics is a very complex field of physics and engineering, but camera lenses don’t have to be complicated to use and understand. The best way to learn is through experience. Here’s your homework: buy (or borrow) a short-length lens, somewhere between 16 and 25mm.

Your lens will arguably have the most important impact on your final image — far beyond the rest of the camera hardware you’ll ever own. Still, how does it actually work to produce a focused image? Plus, what do all the numbers and letters in a lens name mean? Let’s take a look.

As shown in figure 3, the 1/2 of the accessible length that an optical instrument, with a given angular FOV, is able to capture, could be seen as the base of the triangle with a vertex angle equal to 2/FOV, and the height of approximation equal to the distance from the object to the mechanical front the lenses, which is the Working Distance (WD).

Thus, a single object that bends light is called a simple lens. Similarly, a set of two or more lenses working together is called a compound lens.

However, it is worth noting that the equation for accessible length is not accurate, since it was a rare occasion that the entrance pupil (which is precisely the point at which the vertex of our triangle model in the equation should locate.) is positioned at the mechanical front of the lenses.  And the equation becomes invalid for applications with short working distances because the portion of deviation has increased. This is the reason for the fact that computer simulation data are utilized when it comes to the actual designing and planning of the lens architecture.

Now assume, for the sake of the argument, there is an object at an infinite distance from a Biconvex lens, hence the image is formed at the sensor which is one focal length from the lenses. The focal length is f, and the vertical length of the sensor is h.

Cameralens size chart

First, you use another lens–one that straightens the light a little. In fact, that’s how simple telescopes work —  they have one lens to bend the light to make things look larger, then another to bend it again to make it look clearer. In fact, this is how two simple lenses become elements of a compound lens.

Comparatively, if you’ve ever tried to light a leaf on fire with a magnifying glass on a sunny day, you understand exactly how bending light works. You collect and bend the light from the sun onto a specific point, which is the point of focus on the leaf.

The focal plane of a lens is controlled by the size of your aperture. The bigger your aperture, the narrower your focal plane. Most modern lenses have an adjustable aperture. Aperture is usually measured in f-numbers or f-stops, though on some video-specific lenses they’re called T-stops instead.

Howdocamera lenses workphysics

Now that we have a basic idea of how a lens works, let’s get into some of the technical nitty-gritty. When you buy a lens, it usually comes with a bunch of numbers and letters in the name, like “Nikkor 20mm f/1.8 AF”. The first part of that name is simple: Nikkor is the brand name.

Camera lensesmm Explained

In general, it’s important to note that focal length and focal distance are not always related! Two 20mm lenses from different manufacturers may have very different focal distances. Focal distance is not usually in the name of the lens, so you will have to check the tech specs to find it.

In short, the farther away you need to be from your subject, the higher the focal length should be. A 300mm lens is great for shooting wildlife, because you can be far away from your subject. It takes a narrow shot so your subject takes up more of the frame.

Similarly, if you have a wide focal plane, their entire face — nose, eyes, ears — is in focus at the same time. In general, you don’t usually want to shoot with a very narrow focal plane. That said, sometimes it’s necessary because of lighting conditions or because you want a specific artistic effect.

Diagonal FOV measured in length unit could be seen as the hypotenuse of a right triangle with two sides equal to the horizontal FOV and the vertical FOV, hence:

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In comparison, there is also a convex lens with a focal length of 2f, given that the sensor size is the same, now the FOV of this imaging device is:

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The smaller the number, the bigger the aperture. Yes, this seems backward. It isn’t really, but that’s a different article. Aperture is usually in the lens name, and typically indicates the maximum f-stop for that lens. It’s the “f/1.8” in “Nikkor 20mm f/1.8 AF”.

The letters at the end of a lens name can stand for a bunch of different things, which vary from manufacturer to manufacturer. While “AF” almost always means autofocus, there is no standard guide for other letters.

Shoot a subject with it at a low aperture, then a high aperture. Then, get a longer lens (at least 80mm) and shoot the same subject again at a low and high aperture. Lastly, compare the images. Let us know how it turns out on the Videomaker forums.

Focal length is a measurement of the extent to which the light converges or diverges in an optical system. For a Biconvex lens, Focal length is defined as the distance from the optical center and the point where lights parallel to the optical axis converge (the focal point). In more practical terms, given that the object is at an infinite distance away from the optical lenses, the focal length is the distance between the sensor/detector and the optical center of a lens module (This, however, is only an approximate measure, since in real life object at an infinite distance away is only a theoretical concept that does not exist, lights emitted from the objects, entering the lenses, could never be genuinely parallel, but always incident at a certain angle to the optical axis. Therefore, to obtain the most lucid image, the distance between the sensor and the optical center of the lens module will scarcely be identical to the focal length, but rather varied to a minute degree.)

Comparatively, if you want to get up close to your subject, a 20mm lens might be what you need. In brief, this will take a wide shot–so your subject takes up less space in the frame. Zoom lenses, which have a movable sweet spot, will have two focal lengths listed. They’ll have minimum and a maximum like “80mm-200mm”. Furthermore, lenses that can’t zoom are called prime lenses.

Now consider objects at finite distances from the lenses. We use the term Working Distance (WD), the interval between the lens front and the object.

Difference ofcamera lenses

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It is also perceptible from the figures and equations above that a larger sensor will also produce a wider field of view and vice versa.

Focal distance is the closest you can be to your subject and still have it in focus. In other words, focal distance is your minimum focus distance.

To start, imagine a magnifying glass, which is a simple lens. If your magnifying glass is the right distance from whatever you’re looking at, the refraction will make your subject look bigger. This is because the lens gathers light from a wide area, bends it at the right angle, then shoots it into your eye. This functions similarly to the way a funnel might gather and redirect rainwater.

Camera lensesExplained for Beginners

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On the whole, very few professional shooters use manual-only lenses anymore. In fact, autofocus has been standard on most lenses for 40 years. However, most lenses or cameras will have the option to turn autofocus off.

Therefore, conversion between the horizontal FOV, vertical FOV, and diagonal FOV could be deducted using the trigonometric functions:

Types ofcamera lensespdf

In general, camera lenses are almost always compound lenses. To reduce confusion, when we talk about the simple lenses inside a compound lens, we refer to them as elements.

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Filmcamera lensesexplained

Field of View (FOV ) is an important factor needed to be taken into consideration when you buy or design an optical imaging device or component. FOV describes the maximum scope at which an optical instrument could capture visible lights or electromagnetic radiations in the case of infrared thermal imaging. Field of View is measured in terms of the sensor size which forms the image and the focal length of an optical imaging device. Therefore, for beginners, before we start to discuss the field of view, we have to understand focal length first. Incidentally, if you are interested, you can also learn more in our other Optical Basics Series, which is still progressing and might update in the future. If you like these small pieces, you could continue to follow our updates:

As shown in figure 1, FOV, as an angular parameter measured in degrees, is labeled as angle α, and we could see that angle α equals to angle β according to the law of vertical opposite angles. And the value of beta could be solved using the trigonometric functions of the triangle ABC.

Oftentimes, instead of an angular measurement of FOV, there are also circumstances that require a certain viewing scope in terms of distances. For, example, a client purchasing thermal lenses for monitoring production would expect the camera could capture the whole scene of the specific workshop or a certain machine, and it is more tangible to use measurements of length rather than angle.

Likewise, to get even clearer and less distorted images, we add even more elements to unbend and rebend the light exactly right. Plus, we add a mechanism to move those elements around to adjust the bending, and therefore your focus and/or magnification.

Additionally, you might hear about focal plane. Focal plane (also called depth of field) is how deep your area of focus is. It can be hard to explain, but imagine you’re taking a portrait of a person. If you have a very narrow focal plane, if your subject’s eyes are in focus but their nose won’t be, and neither will their ears.

Autofocus means that the lens has tiny, extremely precise motors in it that, in concert with your camera sensor, will adjust the distance between elements and focus your picture automatically. However, some lenses are manual focus only, which means you have to adjust the lens by hand to focus it.

Simply defined, a lens is something that bends (or refracts) the light that passes through it. As you can imagine, lenses are everywhere in our world — from a drop of water on a car’s windshield, to your eyeglasses, right down to your actual eyeballs.

An object viewed through a magnifying glass looks bigger, but it’s usually distorted and fuzzy as well. How do you reduce the distortion of the image and make it sharper?

When you are selecting optical lenses or cameras, these equations about the calculation of FOV and its accessible length could be helpful. You might ascertain the FOV or the length first according to your requirements, and then estimate the focal length, and the sensor size using the equations. Also, you could adjust the FOV of the lenses via changing the focal length, the sensor size, and the working distance. For zoom lenses, the observer could obtain variable fields of view, zooming the lenses and continuous changing the focal length of the lens assemblies. For dual FOV lenses, there is a double focal length resulting in double FOV. These lens modules with variable focal lengths have the advantage of changing the field of view without the location-shifting of the observer, this is of extreme usefulness in the case of LWIR lenses and MWIR lenses, as thermal cameras operating at the aforesaid wavebands are often applied for warfare. For Fixed Focal Length (Prime Lenses), since the focal length is constant, one needs to change the working distance to procure a different FOV, moving toward or away from the target object.