FOCAL LENGTH AND LENS TYPES

Introduction

A photographic lens is an optical lens that is used in conjunction with a camera body. It is also a mechanism to create images of objects either on a photographic film or on any other media that is capable of storing an image chemically or electronically.

Focal length is a term used to describe the size of the lens. It is an optical measurement that refers to the shape of the lens and not its physical dimensions. In more technical terms, lens size is the distance between the rear nodal point and the lens focal point. This is while the lens is focused to infinity.

In other words, the focal length is determined by the distance between the lens and the image sensor. That is when the subject is in focus. Usually, the focal length is generally represented in millimeters, usually abbreviated as mm.

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This information tells us the angle of view for a given lens. Also how much of a scene will be captured using that lens. The focal length determines how “zoomed in” your images appear. The smaller the focal length, the wider the field of view and vice versa.

Lenses are classified based on their focal length and we will be discussing that later in this article. Based on their focal length, lenses are often referred to as a wide-angle lens, normal lens, telephoto lens, long focal length lens, short focal length lens, or as a zoom lens.

Wide-Angle Lenses

A lens with a short focal length is called a wide-angle lens. It is generally characterized by a wider than normal field of view, also called the angle of view.

At very wide focal lengths, an image can appear distorted and fish-eyed. However, carefully placing your subject can eliminate or limit distortion effects. The focal length of a wide-angle lens ranges from 8mm to 35mm on a full-frame camera.

Although wide-angle lens with a focal length of 35mm, 28mm, or even 24mm won’t look particularly wide.

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Normal Lenses

Normal lenses are lenses with a focal length equal to the focal length of the human eye. This is about 50mm when compared to a lens on a 35mm camera. A normal lens works in such a way that the focal length gives a natural perspective and field of view to our images.

A normal lens for any format is equal more or less to the diagonal measurement of the image format. So for a 35mm full-frame format, the image sensor (or film) area is a rectangle 24mm by 36mm. This means that technically, the “normal” lens would about 43mm but a 50mm lens is close to that length. It is easy to manufacture.

Telephoto Lenses

Technically, the term telephoto applies to a specific design of long focal-length lenses, but as of now, the term has broadened and is now essentially synonymous with any long focal-length lens. So a telephoto lens is a long, focal-length lens that will narrow the angle of view and cause apparent image magnification i.e. it brings the subject closer.

For most people, zooming in on a subject generally means using a longer lens. For a full-frame 35mm camera, the focal length of a telephoto lens is any length greater than the normal 50mm.

Typically, the focal length of a telephoto lens can range from 85mm to 2000mm or even greater. The most popular lenses in this range include 85mm, 100mm, 105mm, 135mm, 200mm, or longer. Zoom lenses typically range from 70-200mm and 150-500mm.

Portrait Lenses

Lenses used for capturing a person’s head and shoulders is called a portrait lens. Usually, portrait photographers will opt for a short telephoto lens in the 85mm or 105mm range.

Although a normal or wide-angle lens can also be used for portrait photography, the slight foreshortening of the narrower angle of view, coupled with the ability to blur the background makes the short telephoto lens a perfect choice for a head and shoulders portrait.

Landscape Lenses

For landscape photography, a lens of any focal length can be used just like in portrait photography but for those majestic, sweeping vistas we seek out while traveling cross country, many photographers choose to go for shorter focal-length lenses, preferring their wider angle.

This is because a wide-angle lens allows you to fit in more of the scene into the image area, and it is easier to create an impressive depth of field. So focal lengths such as 20mm, 24mm, and 28mm are common choices for this type of photography even though a normal lens will also work.

Macro Lenses

Macro lenses are a special breed of lenses designed optically for ultra-close focusing. With a macro lens of longer focal length, a photographer can achieve the same magnification ratio of a shorter lens, but from a greater camera distance.

This makes it much easier to add lights if necessary. Typical macro lenses commonly used have focal lengths such as 50mm, 60mm, 100mm, and occasionally 200mm. Some macro lenses are even designed with a built-in flash to aid in exposure.

It is important to state that many zoom lenses have a feature known as macro focusing, but only a few zoom lenses can focus as close as a true macro lens.

Zoom Lenses

Do not be confused as a lot of people tend to be when it comes to differentiating between a zoom lens and a telephoto lens. To many people, a zoom lens is a telephoto lens, since it allows you to “zoom in” on a subject but in simplest terms, a zoom lens can change focal lengths, while a telephoto lens simply cannot.

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A zoom lens is designed in such a way that it can adjust its range to be wide-angle or long telephoto. Although it is not enough to simply say “wide-angle” because the term encompasses a wide variety of focal lengths ranging from 16mm to 35mm.

Also, a zoom lens may not be telephoto at the longest focal length, but it can still achieve wide-angle under 50mm of the normal lens. Zoom lenses come with a lot of differences between them which makes their focal lengths ambiguous.

This is why many manufacturers and photographers will use additional words to accurately describe the zoom lens to avoid confusion. A normal-range zoom lens may range from 24-85mm or 28-105mm.

A telephoto zoom lens could be described as a lens ranging from 70-200mm, 70mm or 100-300mm, or 70-150mm while ultra telephoto zoom could be 150mm, 200-500mm, or 650mm.

All-In-One Lenses

All-In-One lenses are a very popular type of zoom lens, especially for crop-sensor digital cameras. An All-In-One lens allows the photographer to take almost any type of photo using a single lens.

The All-in-one lens can range from significantly wide-angle, to long telephoto, and it can even approach near-macro focusing ability. The focal length for a full-frame format typically ranges from 24-200mm or 35-300mm.

For the crop-sensor camera format, the lens can have even more range and still be of reasonable size, weight, and cost. They come mostly in the 18-300mm range for most crop-sensor cameras. All-in-one lenses, however, are limited. In order to keep size, weight, and cost down, they are unlikely to be very fast which means that they won’t have a large aperture.

Even though they may produce a good quality image, images they produce are generally not as sharp as those produced by other lenses across the focal lengths.

Prime Lenses

A prime lens simply has only one focal length. It can be wide-angle, telephoto, normal, or macro. Photographers who opt for a prime lens are looking for ultra-high image quality or very fast f-stop. As said earlier, it is not unusual to see prime lenses of virtually any focal length.

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A fisheye 8mm is an example of a prime lens, so is a 24mm f/1.4 and a 50mm f/0.95. Some other prime lenses may be telephoto lenses such as a 500mm f/2.8 lens or a 2000mm f/11.

A common feature of all prime lenses is superior image quality, a fast aperture or f-stop, and a very high price. Some modest prime lenses such as a 50mm f/1.8, 35mm f/2.8, or 135mm f/3.5 are smaller, lighter, and cheaper than premium prime lenses, and are able to still deliver some very fine results.

What Is a Crop-Sensor Camera?

I’m sure you must be wondering by now what a crop-sensor camera is. Questions such as how is it different from a 35mm full-frame sensor and how does it behave in relation to focal length and lenses which is our focus for this article must have formed in your mind.

Hold on a second, I will clarify. Simply, a crop-sensor camera just as the name implies has a smaller or cropped sensor than its 35mm full-frame sensor counterpart. The most noticeable difference between the two sensors is in the “crop factor”.

The crop factor is the magnification of the field of view when looking through the viewfinder. Crop-factor digital cameras are some of the most heavily produced DSLR. Also ILC cameras on the market and are generally cheaper than their full-frame counterparts.

A very common crop-sensor format is the APS-C format with a crop factor of 1.5x. Another highly popular crop-sensor format for digital cameras is the 4/3rds or micro 4/3rds (MFT) format with a 2x crop factor.

Let us compare the difference between a crop-sensor camera using the 1.5x crop factor model and a full-frame sensor. A 50mm lens on a full-frame sensor camera will have a field of view of 50mm. Also a 50mm lens on a crop-sensor camera has an apparent field of view of 75mm, i.e. 50mm x 1.5 = 75mm. Simply, your 50mm lens on a 1.5x crop factor camera will “feel and act” like a 75mm lens.

Conclusion

Lenses are classified based on their focal length. Next time you hear of wide-angle lens or telephoto lens, I’m certain you will understand what it means. Also what such a lens is capable of doing since you have read this article.

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Author: Arinze

A Photography enthusiastic. I work with a group of other professional photographers to provide you tips on photography

About Arinze

A Photography enthusiastic. I work with a group of other professional photographers to provide you tips on photography

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