Have you noticed unexpected blurriness toward the edges of your photos? When you shoot at a wide aperture, do you find your images lacking clarity, despite being correctly focused? You’re likely experiencing a phenomenon known as spherical aberration.
Spherical aberration is a type of optical imperfection common in photography. It is caused by the way light is refracted by your camera’s spherical lens. Luckily, there are a few ways to correct, or minimize spherical aberrations for clear, sharp images.
What causes spherical aberration?
The abnormality occurs when light passing through your lens doesn’t come together at a single focal point. Light rays are refracted differently depending on where they enter the lens. Light rays that pass through the center of a spherical lens do not refract as much as those that pass through the edge.
Because light rays refract at different degrees, they don’t converge at a single focal point. As a result, portions of your image appear blurry.
The shape of your lens is, by far, the most common cause of spherical aberration. However, lens quality and placement of elements within the lens housing can also play a role.
Spherical aberration can cause a few unexpected issues for photographers. You might notice a slight halo or ghosting effect in your image. It can also lead to a loss of fine contrast across your image. However, the most common issue caused by spherical aberration is noticeable blurring toward the outer edges of your photo.
How to reduce spherical aberration
Spherical aberration won’t be a problem for every photographer or in every photo-taking situation. In fact, many photographers, especially those that primarily shoot portraits or macro shots, will never notice the imperfection in their photos. But, if you shoot with a wide aperture and expect clear focus to the edges of your image, there are a few ways to reduce the effects.
Upgrade your lens
If spherical aberration is problematic for your type and style of photography, it may be time to upgrade your equipment. Lenses made from higher quality glass and better coatings tend to have less severe aberrations. You can completely eliminate the imperfection by investing in an aspheric lens or a gradient-index lens. Unfortunately, these lenses can be quite expensive.
If upgrading your equipment isn’t an option, try stopping down. Simply increase your numerical f-stop number to reduce the amount of light entering the lens. Often, only a half or single stop down can considerably increase sharpness.
Sharpen in post-processing
Any camera with a spherical lens is capable of producing spherical aberration, particularly at wide-open apertures. But, if you know when and why it happens, it’s easy to make adjustments that reduce the effects.
Spherical aberration is most apparent in photos taken with a lower f-stop. Click here for more in-depth information about aperture and the role it plays in photography.