Let's say you use a wide-angle lens to shoot a portrait photo. Normally, you would step in close to fill the frame. But what if you do not step in to fill the frame and instead shoot from a distance and crop the image?

Mustache Distortion, also known as complex distortion, combines both barrel distortion and pincushion distortion - creating a wavy image similar to the shape of a mustache. This type of distortion occurs less often than barrel distortion and pincushion distortion, but it is not a rare phenomenon in photography.

If the human eye is the sensor, then all visible wavelengths are seen simultaneously, and monochromatic radiometric variables, IOPs, and AOPs must be replaced by broad-band values that depend on both the wavelength dependence of the ambient radiance and on the relative sensitivity of the eye to different wavelengths. This is effected by replacing these quantities by their photopic equivalents.

These differences make some parts of the image appear misshapen, even though every object is focused and sharp. The causes of lens distortion are different depending on the type of lens distortion. For example, barrel distortion often occurs in wide-angle lenses because the view of the lenses is wider than the camera sensor. This is why the center of the image will appear bigger while the edges will appear smaller.

This distortion elongates the corners of the image, creating a shape that is similar to how a pincushion looks when you push a pin on it. This distortion occurs more often in zoom telephoto lenses, such as lenses longer than 200mm in focal length. Images shot with these lenses tend to show the reverse effect of barrel distortion, which means straight lines appear curved inside rather than outside.

The position of the camera itself causes perspective distortion. For example, if you photograph a building from a lower angle, its shape may look different from when you take the picture from a straight angle. Perspective distortion can also make more distant objects appear smaller than closer objects.

Not all wavelengths of light evoke the same sensation of brightness in the human eye-brain system. For example, suppose a person with “normal” eyesight is exposed to monochromatic radiance of wavelength 550 nm and magnitude of 103Wm−2sr−1nm−1. (This is comparable in magnitude to the sun’s spectral radiance at this wavelength when seen through a hazy atmosphere or at a large solar zenith angle.) The person will “se” a bright yellowish-green light. However, if the person is exposed to light of the same radiance magnitude, but of wavelength 300 nm, the person will not “see” anything because the eye is not sensitive to this ultraviolet wavelength. However, if the exposure lasts long enough, permanent and severe damage will be done to the eye by the ultraviolet radiant energy.

LuminanceRGB

Although wide lenses and zoom lenses are not as “dramatic” as fisheye lenses. They are also prone to creating this barrel-like effect where the middle of the picture is much more magnified than the edges. You may have noticed this type of distortion when shooting architecture or buildings where walls appear to be curved outwards, or minarets appear to be curved or slanted.

Go ahead and try this on your own to see how it works for you. First, capture a portrait image using an 85mm lens or any portrait-length lens. Next, swap the 85mm lens with a standard wide-angle lens without moving or changing the subject's position. A 16 to 35mm or an 18 to 55mm lens would do. Shoot from the same location and crop the composition to match the first image. The two compositions are identical.

This type of lens is often used in photography to create optical illusions, such as making objects appear gigantic or very small compared to their actual sizes. The camera’s position and angle create a certain perspective that makes the object appear differently than its actual shape.

Illuminance

The normalized photopic luminosity function is denoted by ȳ(λ). The spectral radiance L(λ), weighted by ȳ(λ) and integrated over all wavelengths (in practice, usually from 380 to 720 nm or even just 400 to 700 nm) gives the luminance Lv, which is the photopic, or vision, equivalent of radiance:

Some distortions are visually unnoticeable because they are too subtle to disturb the appearance of the overall image. This can happen when the various parts of the convex-shaped lens have different focal lengths that cause different magnifications.

Luminance

As seen in the units of Km, the lumen is the visual correspondent of radiometric power in watts. The SI base unit for photometric variables in the candela, abbreviated cd. The definition of the candela is “The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.” (This frequency corresponds to λ = 555nm for light in a vacuum.) Recall that radiometric intensity is power per unit solid angle. The candela is correspondingly luminous power per unit solid angle, i.e. 1cd = 1lm, sr−1. The lumen is then a derived quantity, which by definition is 1lm ≡ 1cdsr. Unsuccessful attempts have been made to have the lumen adopted as the SI base unit; the proposed definition being “the lumen is the luminous power of monochromatic radiant energy whose radiant power is 1/683 W and whose frequency is 540 × 1012Hz.” Neither of these definitions is particularly enlightening, so for intuitive purposes, think of an ordinary candle as having a luminous intensity of about 1 cd, or 1lmsr−1. The candela (Latin for candle) indeed traces back to the historical use of a “standard candle” as the unit of brightness. (One of the historical definitions of a standard candle was the “light produced by a pure spermaceti candle weighing one sixth of a pound and burning at a rate of 120 grains per hour.”)

Table 2 shows typical illuminances Edv. In illumination engineering, one lumen per square meter is called a “lux.” Thus the instruments used to measure brightness is rooms are often called lux meters (photographers usually call them light meters).

On Adobe Lightroom, you can choose the Lens Corrections menu and use the automatic profile correction to fix your image. You can click this menu and select the lens you used to take the image. This feature will automatically correct lens distortion and vignetting at the same time.

Wide-angle lenses are primarily used for architecture photography, and they also tend to produce the most common examples of images with barrel distortion. Interestingly, however, barrel distortion can be easily corrected in post-production. Most editing software, including Adobe Lightroom and Photoshop, comes with lens profile adjustment. To use this feature, you select the correct profile, and the software automatically corrects the lens' distortion.

There is an alternate theory in photography that states lens distortion does not happen at all, at least not solely because of the lens we're using. The alternate theory considers that regardless of the focal length of the lens we are using, if we do not move in close to fill in the frame with the subject, then lens distortion will not happen.

When you take a picture too close to the object, the chance of lens distortion occurring is even greater. It may also create a perspective distortion and give you another problem to deal with in post-production. This is why you must keep a distance between yourself and the object you want to photograph.

Here Km is a fundamental physical constant called the luminous efficacy that by definition has the value Km = 683lumenW−1 exactly. (See the Units page. This quantity converts radiance from energy units (Watts or Joules per second) to the visual unit of lumens (abbreviated lm). The numerical value of Km traces back to the idea of the visual brightness of a “standard candle.” The modern definition of a lumen is that the surface of melting platinum (at a temperature of 2042 K) emits luminance of 6 × 105lmm−2sr−1. The luminance Lv corresponds to the visual impression of brightness. The subscript v (for visual) on a radiometric quantity flags it as the corresponding photometric quantity.

In most cases, the software will automatically detect the lens you have used to shoot an image and allow you to correct any distortion. So usually, it is just a one-click matter to correct.

Barrel distortion, also known as negative distortion, is a lens distortion in which the lines protrude outwards at the center, like barrels. Barrel distortion happens when the picture’s center is magnified and the edges are somewhat shrunken.

Although lens distortion appears more often in certain lenses, such as wide-angle and fisheye lenses, it is actually more common than you would think. And you should cut yourself some slack because there is no perfect picture, considering that every picture actually has some amount of distortion in it.

This can happen the other way around, where the pincushion happens in the middle and gradually turns to barrel distortion toward the edges. This distortion occurs more in older camera lenses.

The phenomenon creates an effect where the lines are curved around, creating a spherical shape that resembles a barrel. Barrel distortion happens most frequently in wide-angle lenses, especially fisheye lenses.

On the other hand, lens distortions happen because of the shape of the lens itself, as we have previously discussed. It can happen no matter how you place your camera. Of course, the distortion may appear worst at a certain angle, but even when you just take a picture with a straight eye-level angle, the distortion can still be visible.

The automatic profile correction will help you for the most part, and you just have to take some further steps to get the desired result. But sometimes, the automatic profile correction cannot help, especially in severe distortion cases, so you must fix it manually on the Transform Tab. The Transform Tab also has an automatic setting. You can try it to see if it helps, but if it does not, you can still use the menus provided below:

Photometric equivalents of apparent optical properties are obtained from the photometric variables just as AOPs are obtained from radiometric variables. Thus the illuminance reflectance is given by

This feature will provide you with a grid that you can use as a guide. By turning on the grid, you can easily see the curved and distorted part of the image.

In mustache distortion, the barrel distortion magnification appears in the middle of the focal length, and the pincushion distortion gradually takes over around the edges.

Barrel distortion is one of the primary reasons photographers do not shoot portraits with a wide-angle prime or zoom lens. This is because, with a wide-angle lens, you must move closer to your subject to fill the frame. When you do that, you invariably place the subject’s facial features right in the middle of the section where lens distortion starts to happen. You will notice that lens distortion mostly affects the nose, ears, and top of the head.

Does this mean lens distortion does not happen at all? No, it still happens, not solely because of the lens's optical design but also because of the distance between the lens and the subject. So, if you move in close, lens distortion will be unavoidable, and if you don’t, it can be avoided.

Lens distortion is a distortion caused by camera lenses falling short. Usually, this phenomenon is related to the structure of the lens itself, but the light reaching the camera sensor may also cause lens distortion.

Luminous intensity

Pincushion distortion, or positive distortion, is basically the opposite of barrel distortion. Instead of getting the image magnified at the center of the focal length, the lines are hunched inwards and appear smaller in the middle, making edges appear bigger.

Most of the menus mentioned will help you get through most distortion cases. However, in very severe cases, you may still need to take extra steps to fix some parts of the image that appear curved. You can use the transform slider to fix both vertical and horizontal lines manually.

This tool will help you correct barrel and pincushion distortion more easily in one single step. Note that the more adjustments you make, the more likely you will need to crop more parts of the image. Keep this in mind every time you take a picture so that when you encounter some objects such as buildings. You know you will need to do some lens distortion correction later; you can make sure you leave enough space for cropping.

The auto menu balances and corrects both vertical and horizontal distortion. It also helps balance your picture without having to crop some parts of it.

Most lenses nowadays are already pretty good at avoiding distortion occurrence. Older lenses, however, tend to create more distortion. So, select your lenses carefully before you take some pictures. Many photographers recommend using 50mm lenses to avoid lens distortion.

Compare such a cropped image with an image shot by a normal portrait lens like 85mm or 135mm. You will notice that the composition appears the same.

and so on. Just as irradiances can be computed from radiances, illuminances can be computed from luminances by equations of the same form as for radiometric variables. For example,

Lens distortion is an optical phenomenon caused by one of the types of lens failure. Lens distortion happens when the camera fails to be rectilinear.

The full menu has a function similar to that of the auto menu. It will balance out the overall image. The full menu can be used in extreme distortion occurrence, but some parts of the image might be cropped.

There are several methods you can use to fix lens distortion. One of the ways you can do this is by fixing it in the post-production process using photo editing software such as Adobe Lightroom, Photoshop, and Luminar Neo.

One of the things you can do is prevent lens distortion altogether during the production process. There are some ways you can do to prevent lens distortion below:

Visible light

Pincushion distortion happens when the magnification increases with the distance. This is why pincushion distortion occurs more often in zoom telephoto lenses: the further the distance, the bigger the magnification.

Spectral sensitivity curve

All radiometric quantities have a photometric equivalent obtained by an equation of the form of (1). Thus the photometric equivalent of the downwelling plane irradiance Ed(λ), which is called the downwelling plane illuminance, is given by

This menu will help you a lot when you correct the distorted image manually. The guide menu will provide you with lines you can use as a guide. Following these guidelines, you can easily see the part of the image that is still distorted and needs fixing.

For conversion of night-time, or dim-light, radiances to luminance, an equation of the same form as (1) is used but with the scotopic luminosity function, denoted ȳ′(λ). The conversion factor for the scotopic luminosity function is Km′ = 1700lmW−1. Thus the rods are more efficient at converting radiant energy into visible light, but at the tradeoff of giving only gray-scale images.

It is called lens distortion because even when other factors may contribute to distortion, the lens is the most probable cause. Unlike perspective distortion, lens distortion is purely an optical phenomenon caused by the shape of the lens itself. To understand this phenomenon further, we also need to learn the difference between lens distortion and perspective distortion.

There are several types of lens distortion. Although the appearance of lens distortion can be irregular and with random shapes. There are at least three kinds of lens distortion that appear most often in photography.

What is rectilinear? Rectilinear, in photography, is the lens’ ability to “preserve” the straight features in buildings, walls, doors, and other objects to appear straight in the picture. Simply put, it keeps straight-looking objects straight, not curved.

The photopic and scotopic luminosity functions are plotted in Fig. 1. These functions are empirically derived averages based on visual response studies of numerous humans. In these studies a colored light is viewed next to a reference light. The observer adjusts the power of the colored light until it subjectively appears to have the same brightness as the reference light. The reciprocal of the measured radiance of the colored light is then plotted at the wavelength of the colored light. This process of “brightness matching” is subjective and there is considerable variance among observers, so the resulting average over many observers has somewhat the same statistical validity as the “average American male, age 30.” Nevertheless, the functions serve as reasonable reference standards for human eye response. Suppose, for example, that monochromatic radiance L(λ = 500nm) (blue-green light) of some given magnitude (in Wm−2sr−1nm−1) evokes a certain qualitative sensation of brightness in the eye. Then from Figure 1 we see that in order to produce the same sensation of brightness with red light of wavelength 650 nm requires about three times the radiance, i.e. L(λ = 650) ≈ 3L(λ = 500).

This lens is also known for not having optical distortion issues. Lens distortion can be annoying if you do not expect it, but sometimes, it does not have to be bad. Some photographers intentionally distort lenses to create a certain perspective or an optical illusion in their images. You, too, can use lens distortion creatively and experiment with different types of photos.

Again, just like in barrel distortion, in pincushion distortion, straight lines appeared to be affected more than anything else. Therefore, an open roof that is placed at about 1/2 to 1/3 of the frame will tend to have the effects of pincushion distortion more than anything else in the frame. The effects of pincushion distortion are maximum towards the age of the frame. As you move toward the center of the frame, the effects appear negligible.

Photopicresponseof human eye

Both Lightroom and Photoshop are excellent tools for removing lens distortion. You can use one or even combine both of them. However, sometimes, removing some kinds of lens failures in the post-production process does not always give you the best result.

It is particularly important to add some space around the object. This step will help you a lot in post-production. First of all, by adding some space around your object, the object itself could be safe from distortion, and only the edges, which is the extra space that is being distorted. The extra space is also extremely useful in post-production work, just in case you need to do some cropping.

Luminous flux

Page updated: May 19, 2021 Author: Curtis Mobley View PDF

Some kinds of lenses such as wide-angle lenses are more likely to distort and stretch images for the sake of capturing all angles. As a result, some straight features that should appear straight in the picture appear distorted and curved. This is basically what lens distortion is.

The relative ability of radiant energy of different wavelengths to evoke differing sensations of brightness in the human observer is described by luminosity functions. The cone cells of the human eye are responsible for color vision at daylight levels of the ambient illumination. These cells have a sensitivity described, when averaged over many individuals, by the photopic luminosity function. The rod cells are responsible for vision in very dim light, such as at night. These cells are more efficient at seeing blue wavelengths and less efficient at red wavelengths than are the cones. The eye sensitivity at low-light conditions is given by the scotopic luminosity function.

Instead of forcing the camera to fit a wider view into a single frame, maybe you can consider taking some steps back and taking the picture from a distance to get a wider view.

As an example, we can compute the luminance of the sun. The Sun’s output can be approximated as that of a blackbody at a temperature of T = 5782K. The radiance of a blackbody is given by Eq. (6) on the blackbody radiation page:

This tool is very helpful in straightening the curved lines. Use the slider in the transform tab to adjust the vertical and horizontal perspective, following the grid as a guide.

Wide-angle lenses always create distortion. That is what you can expect because they basically squeeze a wider view into one single frame. So, lens distortion is normal when you use this kind of lens, especially the ‘extreme’ ones, such as the fisheye lens.

This is one of the reasons photographers choose slightly longer focal length lenses like 50 to 200mm for portraits. Lenses like these do not reflect the effects of barrel distortion.