Camera Lenses Explained

It is not unusual to see someone taking selfies or snapping away photos using a mobile phone camera. Camera phones have become the camera of choice surpassing stand-alone cameras. Phone manufacturers have responded to this trend by making phones with cameras that rival traditional stand-alone digital cameras. One of the recent developments is multi-lens phone cameras. Mobile phones such as iPhone 13 or Galaxy s22 have three lens cameras: wide, ultra-wide, and telephoto. What do all these camera lenses do, and how can we use them to enhance our photography? Let us start by understanding what lenses are.

What is a lens, and how it works?

A lens is a piece of glass that alters the direction of light waves. Typically, light travels in a straight line, but its projection changes when it goes through a lens. Lenses change the direction of light because their surface is not flat. It’s curved. Lens curvature is essential because it bends light waves and hence affects light direction. When light rays pass through a lens, they will bend towards the thicker part of the lens curve. Therefore, the type of lens curvature determines where the light wave hitting the lens will end up.

There are two main types of lens curvature—concave curved inwards and convex curved outwards. Because concave lenses are thicker at the top and bottom, light waves passing through them will either bend upwards or downwards depending on where they hit the lens. Thus, light waves that hit the top half of the lens take an upward trajectory while those at the bottom half bend downwards. For this reason, we refer to concave lenses as diverging lenses. Note that light waves that pass through a concave lens will forever remain parallel because of the projection they take.

Convex lenses affect light waves differently. As mentioned above, light waves constantly bend towards the thick part; therefore, in convex lenses, which are thicker in the middle, light waves take an inward projection. By bending light this way, all the light rays passing through a convex lens will eventually intersect at a point. Because of this characteristic, the term converging lens is used to describe convex lenses.

Convex lenses have the ability to converge incoming light waves to a point. Concave lenses cannot. They affect the direction of light so that the light waves when they pass through the lens are perpetually parallel. Although this way of affecting light waves may seem counterproductive to photography, they are still very useful. For example, in a zoom lens, concave lenses are used to alter the size of the incoming light waves.

Concave and convex lenses are both essential to photography. Modern camera lenses, particularly zoom lenses, use both types of lenses. But the primary lens type which is also crucial to creating a photograph is the convex lens. This lens is essential because it converges all light waves at one place called the focal point.

Focal point is crucial because it is where light waves meet to form an image. When this point falls on the sensor/film, the camera records it as a sharp viewable image. Camera manufacturers, therefore, must calibrate the lens accurately so all the light waves converge on the sensor/film.

To achieve this, lens manufacturers measure the distance the lens will require to bring light waves to a point (focal point). This distance from the lens to the focal point, measured in millimeters, is the lens’s focal length. All lenses have a focal length, either a single number for prime lenses or a range of numbers for zoom lenses. Focal length is significant because it affects the lens’s angle of view, the basis of lens types.

Wide-angle and telephoto lens

As mentioned, lenses have different focal lengths. Some lenses require a short distance to converge light rays, and other lenses need a longer distance to do the same. The difference in focal length is very significant. It impacts how the lens views and interprets the scene. We will discuss this in more detail below. What we need to know, for now, is that we can group camera lenses into two general types based on their focal length—wide-angle and telephoto lens. To understand the two types, we must first discuss the human eye.

Lenses work by mimicking the human eye. But because of the eye complexities and stereoscopic human vision, they fall short. For example, having only one lens, a camera cannot fully imitate the stereoscopic view of human vision. The best a camera lens can do is represent a three-dimensional world in two-dimension. Therefore, we will limit the comparison between the two to the field of view.

Field of view is the amount of the scene a lens can capture. This includes both horizontal and vertical spans of view. Suppose, for example, you want to photograph a tall building. If standing close to the building, you will need a lens with a wide-angle of view so you can fit the whole building within the frame.

The human eyes’ standard field of view is about 60 degrees (note this does not include peripheral view, which can make the eyes’ field of view as wide as 120 degrees. Click here to read more1). The consensus among photographers is that a lens at 50mm on a full-frame camera gives a similar natural field of view to that of the human eye.

For this reason, photographers consider a 50mm lens as a standard lens as it closely mimics a human’s angle of view. Because 50mm is normal, any lens with a wider field of view more than 50mm, is technically a wide-angle lens. And those with a narrower field of view, less than a 50mm lens, are considered telephoto lenses.

Note that this is not an exact science. Up to now, there is no consensus among optical professionals if, indeed, 50 mm is the magic number. Other professionals have argued that 46 mm better represents natural human vision, while others put the number past 50mm.

There are differences in sensor/film size (crop factor) that affect the lens’s field of view to complicate the debate further. For example, a 50mm lens on a cropped Canon sensor will effectively have a longer focal length than the same lens on a Nikon cropped sensor camera. So, canon with a 1.6 crop factor will give a 50mm lens the equivalent of an 80 mm lens. While for Nikon with a 1.5 crop factor, the same 50mm will be equivalent to a 70mm lens on a full-frame sensor camera. (You can find the full-frame equivalent of your cropped sensor camera by multiplying the crop factor of your camera with the focal length of the lens).

For this reason, a range of accepted focal lengths is a safer way of determining if a lens is normal or not. The accepted range for a standard lens is then 35mm to 60mm. This range of focal lengths has a similar field of view and similar lens distortion. The differences become more noticeable when you go higher than or lower than the range. For example, when you go lower than 35mm, the field of view becomes wider than what is considered normal. The opposite is true: when you go higher, the field of view becomes narrower than the norm. This is the reason we have wide-angle and telephoto lenses.

Wide-angle Lenses

Wide-angle lenses are lenses that have a focal length of less than 35mm. Thus, they have a shorter reach, meaning you must be closer to the subject to fill the frame, but have a significantly wider angle of view than a standard lens. As mentioned, the effect of focal length on the angle of view is a sliding scale. For this reason, wide-angle lenses are further broken down into subcategories of normal, midrange, and ultra-wide-angle.

The difference between normal, midrange, and ultra-wide-angle camera lenses is the breadth of the angle of view. Mid-range and wide-angle lenses have a wider field of view than normal wide-angle lenses. As the angle of view gets wider, their look and effect on the image become more pronounced. Ultra-wide-angle lenses, therefore, have a distinct look compared to the other two categories. The image they produce is noticeably wide, distorted, and roundish. A fisheye lens is an example of an ultra-wide-angle lens, and indeed, they produce distinct photographs.

Telephoto Lenses

Telephoto lenses are more or less the opposite of wide-angle lenses. They have a more extended reach, but their field of view is narrow. The relationship we saw between focal length and lens attributes also applies to telephoto lenses, though in the opposite way. With telephoto lenses, the longer the focal length, the longer the reach, but the narrower the field of view. There are four subcategories of telephoto lenses based on their focal length: normal, mid-range, and super-telephoto.

A normal telephoto lens is any lens whose focal length is between 70mm to about 135mm. These camera lenses are shorter and smaller in physical size and hence easier to carry around. A mid-range telephoto lens is any lens whose focal length is over 135mm but no longer than 300mm. These lenses are longer and heavier compared to a normal telephoto lens. Their reach is also more extended, and the angle of view a little narrower. Finally, a lens with a focal length longer than 300mm is a super-telephoto lens. These lenses are more elongated, bulkier, and heavier, hence exceedingly difficult to use handheld. But their reach is super extended, although the angle of view is narrower.

Effects of wide-angle and telephoto lens

As mentioned, the significant difference between wide-angle and telephoto camera lenses is focal length, which affects a lens’s field of view (we will go into more detail later). Because wide-angle lenses have a shorter focal length, their angle of view is wide. On the other hand, telephoto lenses have a narrow field of view because of their shorter focal length. These differences are significant because they influence how the lens interprets the scene. For example, if you were to photograph a scene with a telephoto and wide-angle lens, the resulting images would have two distinct looks. The differences in how lenses represent a scene are mainly because of three factors; lens compression, distortion, and field of view.

Lens compression

Compression is how a lens portrays the relationship between objects close to the lens and objects further away. Thus, a lens can either make objects that are further apart appear closer together or vice versa. How the lens will compress the scene depends on the lens’s focal length; hence wide-angle and telephoto lenses will compress the scene in reverse to each other.

A wide-angle lens decompresses the scene, meaning the distance between near and far objects seems to increase. Therefore, objects that a human eye or a standard lens will see as closer together will seem further apart when viewed with a wide-angle lens. This way of rending objects means that objects closer to the camera appear bigger relative to objects further away. If, for example, you take a wide-angle image of a stretched-out arm, the hand, because it is closer to the lens, will look disproportionately bigger and further away from the head. Wide-angle lenses, therefore, increase the sense of depth in a picture.

The opposite is true for telephoto lenses – they decompress. Telephoto lenses reduce the relative distance between near and far objects. Things that are physically farther apart will seem much closer together when viewed by a telephoto lens. By diminishing the scene’s depth, objects further away from the lens appear bigger and closer, similar in size to objects closest to the lens (this is one factor that creates a bokeh effect). While wide-angle lenses increase the sense of depth, telephoto lenses reduce it.

Lens distortion

The reasons for lens distortion are complex. For the sake of simplicity, distortion occurs when a lens renders an image curved instead of flat. Although technology has advanced over the years, the capabilities of lenses are still not complex enough to capture and represent reality accurately. Lenses, unlike our vision, have a lot of limitations to capture a three-dimensional world. Human vision can accurately see and make sense of this three-dimensional world. Lenses cannot. Instead, they take this three-dimensional world and convert it into two-dimension, which does not line up in most cases. This failure in conversion, together with lens imperfections and curvature, stretches objects close to the edge of the lens. The result is lens distortion.

Camera lenses distort in two ways, appropriately named barrel and pincushion. Barrel distortion is when objects appear to curve in. When distorted this way, an object will resemble the lines on a barrel, hence the name barrel distortion. Wide-angle lenses are prone to this type of distortion, but it is more pronounced in ultra-wide-angle lenses. Fisheye lenses, for example, produce distinct round images compared to normal wide-angle lenses.

Pincushion distortion is when straight lines appear to lean towards the center. This type of distortion appears when you shoot vertical objects facing upwards. Because of differences in magnification, parts near the lens magnify more than the parts further away from the lens. Therefore, the object will appear bigger at the bottom than the top, giving a leaning illusion—for example, photographing trees. Shooting trees from the bottom facing up, creates an image where the tree tips lean in and converge. This is called pincushion distortion and is more pronounced with the telephoto lens.

Field of view

As mentioned, the field of view is the total area both vertically and horizontally that a camera can capture. Suppose you take a series of pictures of an object with different lenses at the same distance; you will notice that some lenses will capture the entire object while others will chop off parts of the object. This is the effect of the lens’s field of view. Camera lenses with a wide field of view will capture more of the object compared to a lens with a narrow field of view, even though they are at the same distance from the subject. What determines a lens’s field of view?

Focal length determines how wide or narrow the lens’s field of view will be. Remember, a 50mm lens mimics a normal 60-degree human field of view; when you lower the focal length, the angle of view becomes wider than the normal 60 degrees. The same applies, though in reverse when you increase the focal length. The more you increase the focal distance, the more you reduce the angle of view. Therefore, focal length determines the angle of view, which identifies if a lens is wide-angle or telephoto.

It is worth mentioning that the focal length and angle of views’ relationship is disproportionate. This means that any increase in the focal length will have the opposite effect on the angle of view and vice versa. For example, a 20 -200 zoom lens set at 20mm have almost a hundred degrees angle of view. But the more you increase the focal length, the narrower the angle of view becomes. So at 200mm, this lens will only have 12 degrees of angle of view (click here to read more).

Tip: There is a way to change how wide or narrow the lens can capture without changing the focal length. It all has to do with subject to camera distance. You can narrow the field of view for a wide-angle lens by moving closer to the subject. For a telephoto lens, moving further away from the subject widens the angle of view.

Choosing the right camera lens

Because of the varied ways telephoto and wide-angle lenses capture and interpret a scene, it is essential to choose the lens which will accurately convey your vision. Even though you can use any lens to take a picture, wide-angle lenses are ideal for portraying a sense of space and depth because of their wide angle of view and how they decompress elements in an image. For this reason, landscape or cityscape photographers widely use wide-angle lenses.

Wide-angle Lenses

Because of the diverse ways telephoto and wide-angle lenses capture and interpret a scene, it is essential to choose the lens which will accurately convey your vision. Even though you can use any lens to take a picture, wide-angle lenses are ideal for portraying a sense of space and depth because of their wide angle of view and how they decompress elements in an image. For this reason, landscape or cityscape photographers widely use wide-angle lenses.

Wide-angle lenses are also handy when shooting in light places. As we have said above, you can change a lens’s angle of view by adjusting the distance between the camera and the subject. But where space is lacking, the best option is a wide-angle lens. Because of their wide angle of view, they can capture more of the scene at close distances. For this reason, plus the sense of depth and illusion of space, wide-angle lenses are a go-to lens for architectural and interior photography.

As useful as wide-angle camera lenses are, they have some drawbacks. The most significant of which is distortion. Wide-angle lenses have a more pronounced distortion, particularly for vertical objects. Vertical objects on the edge of the frame, such as trees, will appear to lean or curve when shot with a wide-angle lens. Even though post-production or placing vertical objects away from the edge of the frame can correct this problem, it is still a drawback of wide-angle lenses.

Telephoto lenses

Because of their long reach, telephoto camera lenses are ideal when being close to the subject is not ideal. Wildlife and sports photographers, for instance, find telephoto lenses suitable because they can photograph the action without disturbing the players or scaring away wildlife. Telephoto lenses, therefore, enable the photographer to get close to the subject without disturbing the subject or risking the photographer’s life.

Reach is not the only benefit of using telephoto lenses. As discussed above, telephoto lenses have a compression effect. This effect creates a flattering looking in people, particularly facial features which appear more proportional and smaller. Portrait photographers, therefore, love to use telephoto lenses when shooting portraits. Most photographers will argue that 70mm is the absolute minimum focal length for shooting a portrait.

Final Thought

Knowing what lenses are and how to choose them is a skill all photographers need. Knowing and choosing the right lens will help bring your idea to life. There is a caveat, though; photography is not an exact science. It’s an art form; therefore, your lens choice will depend on your artistic goals and needs and not on the established use of a lens. There are photographers, for example, who take unique portraits using a 50mm lens – a big no-no for most professional photographers. I must admit that it is a tall order, but photographers who understand the workings of camera lenses and who have an unclouded vision of what they want have successfully gone against this norm. As the saying goes, there are no rules in photography.