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Although fisheye lenses radically warp straight lines around the edges of an image frame, any straight line crossing through the dead-center of the frame will still be rendered perfectly straight.

In the last lesson we performed an experiment to focus the light of a candle through a lens. We also learned that to determine the focal length of the system, we move the focusing screen forward and backward until the image of the flame is in focus. Let's consider that candle/lens system for a moment. What do you think would happen if we replaced the lens with one that is twice the diameter with the same focal length? Would the image be twice as bright? Image twice as large? If you guessed the larger lens would make the image brighter, you would be correct. The larger lens has more area to collect light, which actually equates to an image more then twice the brightness at a ratio equal to πr² where r equals the radius of the lens. The image would, however, be no larger since the focal length of the lens is that same.

Be careful, though. An in-your-face view of an actual face can create distortion that looks really weird and sometimes downright unflattering.

Have you ever looked at a photo and thought, “Why does that tiny little barrel cactus appear as large as that distant mountain?” It was simply because you physically moved your camera very close to a small subject, while an enormous subject was far off in the distance.

A simple zoom lens system. The three lenses of the afocal system are L1, L2, L3 (from left). L1 and L2 can move to the left and right, changing the overall focal length of the system.

If your camera and lens don’t have this option, don’t worry. Your next line of defense is your raw processing software. Most modern autofocus lenses will communicate their make and model information to the camera, so you’ll see it in your image’s EXIF data. RAW conversion software such as Adobe Lightroom can read this Exif data and, if you turn the option on, will automatically apply a lens correction profile.

In this article, we will explore all the different types of lens distortion. We’ll go over the various optical flaws in a lens, as well as types of natural distortion that our own eyes experience.

Macro lenses are describe by their magnification factor, meaning that a 1:1 lens will produce a true to life image on the detector. A 19.05mm penny will produce a 19.05mm image on the detector, taking up over half of a full 35mm detector or nearly 80% of a cropped frame sensor (what you will find in most lower end cameras). A magnification factor of 1:1 is generally the minimum to be considered a macro lens, with other lenses reaching to the 1:10 range (magnifying an object 1mm in diameter into an image 10mm in diameter).

Mustache distortion is most common at ultra-wide focal lengths, on both prime and zoom lenses. It is especially common on affordable, all-manual, ultra-wide lenses such as 14mm primes.

Lens compression is basically the same thing: using your perspective to create an image where two very different-sized subjects appear more similar in size than they naturally would.

Thankfully, today and beyond, optical distortions such as barrel, pincushion, and even the challenging mustache distortion, can all be corrected easily with most photo editing software.

Lens diameterglasses

In other words, your perspective on the scene is distorting the scale of a 6-inch subject and a 6,000-foot subject, making them appear the same size.

This article is the third in a series teaching the basics of photography. We started by learning about the properties of light and how an image is created, and we also learned how a lens bends light to focus individual rays into a single bright image. With this lesson we are going to finish learning the scientific theory of lenses and how to use lenses for magnification in addition to brightness.

Barrel distortion is when any straight line that is parallel to the edge of your frame is curved outward. If your composition has straight lines around all four edges, they would appear like a barrel — hence the name. Barrel distortion is most common on normal and medium-wide focal length lenses, especially zoom lenses.

Lens distortion comes in all different shapes and sizes — literally. Most photographers use the term rather loosely, so we hope this article cleared everything up for you.

In my next installment of Photography Snapshot, we will move further away from the theory of photography and explore the exposure triangle, starting with aperture. We will begin to learn how to manually take control of the images you form and we will start short homework assignments to get you out shooting with your camera.

Most of the time, you’re going to want to fix things like barrel, pincushion, and mustache distortion, because they are simply a distraction that hinders you from capturing the real world accurately.

Now that we have learned about virtually every form of lens distortion that photographers will encounter, let’s talk about how to “fix” undesirable distortion. Stay tuned, because then we are going to talk about how to use lens distortion creatively, too.

Pincushion distortion is when the opposite is the case. Instead of bending outward, a straight line at the edge of the frame is curved inward. This type of lens distortion is common at telephoto focal lengths. Modern lenses have very little. It’s more common on older lenses that cross from wide-angle to telephoto focal lengths.

Every photographer has probably heard about distortion, or lens distortion. However, most have never actually learned what it is, and how it affects their photography.

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This is a very simple trick that you can easily demonstrate yourself: using a telephoto lens, align a distant subject with an even more distant, larger subject. If you get the distances right, you can appear to make a smaller-but-closer subject appear equal in size, or even larger than, a bigger-but-farther subject.

The best part is that you don’t need an expensive, exotic lens to avoid unwanted lens distortion. You can use whichever camera and lens you already own to get started.

Simply put, the term distortion is broadly used. Sometimes people use it to describe any time reality appears weird, or inconsistent with how we think it ought to.

In fact, fisheye lenses often do a better job than corrected “rectilinear” ultra-wide lenses at rendering a subject exactly the same in an extreme corner of the frame and in the dead-center of the frame. Ordinary ultra-wide lenses may keep straight lines straight. However, they still optically warp other subjects in order to do so.

A zoom lens combines lens shape, diameter, and focal length and their respective distances from one another to vary aperture and magnification within a system. While some zoom lenses have close to 30 different optical elements that interact to create an image most zoom lenses have the same basic design, they consist of a number of individual lenses that may be either fixed, or slide axially along the body of the lens. One of the most common zoom lens designs divides the optical assembly into two sections, a fixed focal length focusing lens and an afocal zoom system consisting of a series of fixed and movable lenses. The afocal system's purpose isn't to create a focused image but to simply change the size of the image hitting the detector. The result is a focused image that changes size on the detector.

Diagram of decreasing apertures, that is, increasing f-numbers, in one-stop increments; each aperture has half the light gathering area of the previous one.

In this common category of lens distortion, there are three main types of optical issues that lenses experience. Barrel distortion, pincushion distortion, and mustache distortion.

Simply put, the most common types of lens distortion are usually just the undesirable warping of lines. Thankfully, however, nowadays they are almost always removed automatically. When you understand all the different types of distortion, though, the basic concepts can become powerful creative tools.

That just about covers it in terms of lens distortion. However, this article would be incomplete without mentioning the types of natural distortion that are always visible in reality.

First and foremost, I want to answer this most basic question: what is lens distortion? Generally speaking, when we use this term we are referring to distortion that literally distorts what a “perfect” image ought to look like, especially for a certain focal length and camera angle.

The best option is to correct lens distortion before you even get to see it: in-camera corrections. Most modern mirrorless camera systems have electronic communication with each lens, and the lens actually tells the camera exactly how much distortion it has, and how to un-warp any curved lines so that they are perfectly straight. If you turn on Distortion correction in the menu of your camera, you’ll hardly ever see it.

This is what people are usually referring to when they talk about lens distortion. It’s when a line that is clearly straight, in reality, becomes curved when photographed with a “flawed” lens.

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Also, and most importantly, every photographer should learn how to use both perspective and compression to their creative advantage. Try zooming out to ultra-wide focal lengths, and get really up-close and personal with your subjects.

When we discussed the camera obscura in the beginning of this series, we noted that while a larger aperture to let light in would increase its brightness, it would also decrease the clarity of the image. After adding a lens into a camera obscura experiment, you can understand the relationship between these two variables a bit better. A faster lens (shorter f-ratio) will have a narrower depth of field (smaller plane of focus). Modern DSLR cameras allow a photographer to vary the aperture of their lens, thus changing the f-ratio or speed of their camera.

In photography, you often hear lenses described as a focal length and their f-ratio. The f-ratio describes the relationship between the lens diameter and the focal length and is calculated by dividing the focal length by the diameter of the lens. For example, if a lens were to have a focal length of 50mm and a diameter of 10mm, then the f-ratio would be 50mm/10mm=5 or otherwise referred to as f5. If you were to double the diameter of the lens, 50mm/20mm = 2.5, the f-ratio would be f2.5. As you have probably already concluded, lower or "shorter" f-ratio means more light being focused into the image, and thus a brighter image. The f-ratio and focal length of the lens will almost always be printed on the ring surrounding the glass. If you ever hear someone refer to their lens as "fast" or "slow" they are referring to the f-ratio of the camera. A "fast" lens is one that brings in the most light the quickest, thus having a short f-ratio, i.e., f1.2 or f2.5. A "slow" lens will take longer to collect the same amount of light, so generally the f-stop will be larger, i.e., f8 or f12.

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It may sound advanced and complicated at first, but it’s really quite simple! Let’s dive in and break it down. Ultimately, you will even learn how to use certain types of distortion creatively in your photography!

While the lens focal length will effect field of view, another factor in field of view is detector size. In a DSLR you will generally have either a "cropped" sensor or a full 35mm frame sensor. A cropped sensor is defined by its crop factor or focal length multiplier (FLM); the ratio of a 35mm frame's diagonal to (43.3mm) to the length of the diagonal on the "cropped" sensor. In Canon DSLRs the crop factor is 1.6, while on most other brands of cropped sensors the factor is 1.5. This ratio is multiplied to the focal length to determine the focal length of a lens that would yield the same field of view. For example, a 50mm lens on a Canon cropped sensor would produce similar images to a full framed camera with an 80mm focal length lens attached. The cropped images will always "look" more zoomed in, however this magnification is simply caused by caused by the aforementioned crop factor.

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Also, you can use brute force: most RAW photo editing software has a slider that allows you to manually correct barrel or pincushion distortion, though not mustache distortion.

This type of distortion is difficult to correct because it actually features both pincushion distortion and barrel distortion. It’s a rather diabolical and visually distracting phenomenon.

Say you’re photographing any sort of architecture or structure that has a lot of straight lines. They ought to appear straight in your photograph. However, because of the imperfections in the optics of the lens, the lines appear curved instead.

Most of the time, your eyes will see such things and your brain won’t even notice because you’re naturally accustomed to some level of perspective distortion. Other times, when a viewer’s angle exaggerates this perspective distortion, it can really catch a viewer’s eye, or even be unsettling.

While a larger aperture diameter might increase the brightness and sharpen the focus, increasing the lens magnification will increase the focal length and thus enlarge an image. The amount of focal length that you desire will define how much magnification your lens needs. Think about magnification in terms of how much your light bends. The more curve in your lens, the more your light will bend toward a center focus. Creating more curve in a lens means adding thickness to the lens, thus adding more material to slow the light down as it passes through the lens. So as you can see, magnification affects not only the focal length but also the brightness of an image. We've been talking about magnification in terms of increasing the size of an image, where in almost all photography the image you create is significantly smaller then the original object. One type of photography where you are looking to increase the size of the image created is called macro photography. Special lenses are designed exactly for this specialized purpose, built with a long focal length and a very close object to photograph.

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The final piece of the optics puzzle is something called field of view (FOV), in other words how much of the world the detector can see. The FOV of a lens depends on its focal length and the size of the detection surface or camera detector. Let's consider taking a picture of the same object while only varying the focal length of the system. As the focal length increases the FOV narrows, increasing the size of the image on the detector. FOV is fairly simple to visualize by simply following the ray trace in the optical system. One specialized type of lens is a "fish-eye" lens. These lenses are distinct because of their extremely short focal lengths, between 10mm and 20mm, and their bulging glass that looks like a fish-eye. These lenses have a 180-degree or larger field of view, making them particularly good for capturing the entire night sky in a single image.

So far, we’ve been discussing lens distortion which is an optical flaw. However, I absolutely have to mention fisheye lenses. They intentionally distort an image because they use optical distortion to simply fit as wide of a view as possible into the image frame. In other words, if you let straight lines curve, you can have a diagonal (corner-to-corner) angle of view of fisheye lenses that is often a complete 180 degrees, or sometimes more.

Last but not least, you have numerous options for manually correcting lens distortion. First and foremost, if your lens does have a correction profile available, you can manually load it into your RAW conversion software. This is common for all-manual lenses that have no electronic contact with the camera.