So, you’ve set up your shot, making all of your choices for composition and exposure. And something just doesn’t seem right. Maybe your shot is washed out, or maybe the building that’s in the background is seemingly bent, worse yet, it seems that you have a color shifting around your objects in the scene. These are all lens aberrations.
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So, you’ve set up your shot, making all of your choices for composition and exposure. And something just doesn’t seem right. Maybe your shot is washed out, or maybe the building that's in the background is seemingly bent, worse yet, it seems that you have a color shifting around your objects in the scene.
These are all lens aberrations. Lens flares are popular right now, and using them properly can cause a pleasing outcome, but in other situations, they might be subtle and can make a great shot less than desirable. Lens distortion, can be an effect that plays with space compression as well as bending converging lines, but when not wanted, can be hard to escape. Chromatic aberrations are almost never wanted. Knowing what they are, why they are there and how to avoid them, can really improve your shot. And lastly, vignetting. A vignette can focus your viewer to the middle of the screen, but if unwanted, will challenge the eye to see anything but that center. Knowing what kind of vignette you are experiencing and using them to your advantage, is a skill that will pay off.
The design of a lens will affect how easily and what type of flare it produces when a bright light source catches the lens either intentionally or unintentionally. This phenomenon can result in multiple artifacts across your image, and can reduce the overall contrast as well, giving it a washed out look. The specific characteristics of lens flare depend on the lens and iris design. All things, being equal, wider lenses are more susceptible to flares, because they are taking in a much wider field of view. Many manufacturers provide lens hoods specifically designed to reduce this, as well using a matte box with barn doors will help to block out the flare. On some lenses, the lens manufacture will put on special coatings on the lens elements in order to try and minimize the effect. However, the easiest correction for dealing with lens flares is if possible moving the camera till the flare is gone.
Conversely, lens flares are part of a popular aesthetic, sometimes even created for a stylized look. If your goal is to use a flare for artistic gain, make sure you are controlling the flare, and that its only offering a pleasing flare. Because lens flares can wash out a shot, having too much flare, or a flare from the wrong angle causing it to be in the undesired place in your composition, make sure the flare is deliberate, and is as controlled as possible. If you are unable to control the flare, there are ways to add them in post production.
A lens is made up of separate elements that bend light in order to create an image. Many lenses are designed to be rectilinear. These lenses are designed to faithfully represent what you see with your naked eye, and keep straight lines in your image from curving. There are some lenses that are curvilinear, such as fisheye lenses, which don’t attempt to counteract the natural distortion of the lens. Whether it’s by design or accident, optical distortion occurs when the straight lines of the real world appear curved in the image you capture.
There are three main types of optical distortion to be aware of. Barrel, pincushion, and complex.
Barrel distortion will cause straight lines to curve toward the center of your image. This type of distortion is most commonly found in the wider end of a lens.
All other things being equal. The smaller the lens diameter gets, the more drastic the effect of barrel distortion becomes.
When the camera is zoomed all the way in to telephoto, we are only using the very center of the lens to capture an image reducing or eliminating the effects of barrel distortion.
Pincushion distortion will cause straight lines to curve away from the center of your image. This type of distortion is most commonly found on the telephoto end of a lens.
Complex distortion, sometimes called mustache distortion is a combination of barrel and pincushion distortion. Typically exhibiting barrel distortion near the center and pincushion distortion near the edges.
It’s important to clarify that optical lens distortion shouldn’t be confused with perspective distortion. Perspective distortion occurs when a subject and background appear abnormal as a result of their distance from the lens. This actually has nothing to do with the focal length of the lens. These distortions become more apparent when a subject is closer to the lens.
We tend to think of wide angle lenses as having “more perspective distortion”, but the reality is that perspective is the same for any focal length used at the same distance from a subject. But of course we have to get closer to a subject when using a wider lens to achieve the same framing, so the impression is that they have inherently more distortion.
The angle of the camera in relation to the subject can also cause perspective distortion. Shooting upward at a subject like a building will make the bottom of the building look larger, and the top smaller. Conversely, shot downward will cause the top of your subject to appear larger, while the bottom of the subject appears smaller.
Distortion tends to be more noticeable in objects that are closer to the lens.This is particularly true of wider lenses. Manufacturers use rectilinear correction to try and prevent distortion, or in some cases, like a fisheye lens, the distortion is intentionally used to stylize the image for artistic effect
When white light passes through your lens, the different wavelengths of red, green, and blue light refract differently. This is known as dispersion. If you watch older films, or pay close enough attention to footage shot with modern lenses, you might notice some fringes of color throughout an image, or at the edge of high contrast areas. This is known as chromatic aberration.
Lenses use various methods to try and counteract dispersion in an attempt to get you perfect focus with no color shifting. This, however is no simple task. There are two main types of chromatic aberration that can occur. Longitudinal, and lateral.
Longitudinal aberration occurs when a lens fails to focus the colors of light on the same plane. This can result in colored fringes being visible throughout an image. This is typically more prevalent as apertures become wider.
Lateral chromatic aberration occurs when each wavelength is focused on the same plane, but land at different positions. This type is visible along high contrast edges in an image, and doesn’t improve or worsen at different apertures.
Lenses that claim to be low dispersion will theoretically reduce chromatic aberration issues, but the truth is, you just have to use a lens and examine the results to truly make an informed judgement on the presence and severity of this issue.
If you’ve ever noticed that the edges of your image seem to be slightly darker than the center, you’ve see vignetting in action.
In reality there are three types of vignetting that can occur. Optical, natural, and mechanical.
Optical vignetting is a normal characteristic of all lenses. This is caused by light from outer angles being blocked by the lens barrel itself.
Looking at a lens straight on reveals perfect circles, and no light is blocked. However, as you move toward an outer angle, notice that part of the surface of the lens becomes blocked, reducing the amount of light. This holds true in all directions moving away from the center, and causes less light to enter your lens from the outer edges.
This can show as darkened areas around your image, and will reveal itself in the bokeh as well.
This type of vignetting is more pronounced when shooting at wider apertures, and may be reduced or eliminated by shooting at a smaller aperture.
Design compromises with zoom lenses also make these more susceptible to vignetting than prime lenses, and particularly at the wide end of the zoom range.
Natural vignetting is an unavoidable result of physics. The light at the edges of your image has to travel a bit further to hit your sensor than the light in the middle, and natural light falloff causes a reduction in intensity. This type can often be corrected in with post processing.
The light that comes in from the edge of your lens has to travel a bit further to reach the same point as the light that comes into the center, and this means that the light at the edges falls off more, which creates a slightly darker exposure around the edges.
If you’re using a 35mm lens on a camera that has a sensor that isn’t full frame, you’ll also see a reduction in vignetting, because the sensor doesn’t use the outside edges of the image projected by the lens.
Mechanical vignetting occurs when an external attachment, such as a lens hood, filter, or matte box creates vignetting in an image. This is more prevalent at shorter focal lengths on zoom lenses.
All types of vignetting will be more pronounced when focused at infinity.
So there you have it, knowing what lens aberrations are will not only keep you from having them ruin the desire of your shot. But as well knowing how lens aberrations work will allow you to use them to your advantage.