In photography, chromatic aberration is noticeable as ugly colour fringing around an object in your picture and this can really make a mess of an otherwise nice picture. It’s most noticeable when you have a dark object against a lighter background. To demonstrate I took a picture of the top of a tree with the sun and clouds behind it – the perfect sort of conditions to bring out really bad colour fringing.
Zooming in we can see an awful blue fringe around the leaves and this is a perfect example of chromatic aberration and it’s clearly not something we want to see in our pictures but how does it happen?
The easiest way to explain it is with a little bit of highly simplified science. The light we can see, and the light entering the camera lens, is part of the visible spectrum of light:
 |
| Representation of the Visible Spectrum of Light |
School science (if we can dredge up those memories) tells us that white light is the combination of all of these colours and we can prove that by shining sunlight into a prism. The light projected out of the prism looks like the picture above with red at one end and blue at the other:
 |
| Using a prism to show the Visible Spectrum of Light |
The world we see around us is merely white light (or more specifically the light from the Sun or a light-bulb) reflecting and bouncing off the objects around us and into our eyes and our camera lens. Some of these objects absorb some of the different colours differently and that’s how we see different colours. A white object, for example, is absorbing almost no light and is reflecting almost all of it. A black object is absorbing almost all the light and reflecting almost none of it. A green object is absorbing red and blue light and thus reflecting green light; a red object is absorbing green and blue light and reflecting only the red; and so a blue object is absorbing all the red and green light and reflecting only the blue. Everything around us is absorbing and reflecting different colours, or wavelengths, of light and that is what gives the world the colours we see.
Now, and in very, very, simple terms all of these wavelengths (colours) move in different ways through a big chunk of glass like a prism, or indeed, a camera lens. Blue light is very energetic and has a short wavelength. Red light is less energetic and has a longer wavelength. Green light is somewhere in the middle. As all these colours, with different energy, pass through the camera lens, they are bent, or refracted, in different ways. Blue light, with all its energy, bends more than red light. The whole purpose of the lens is to focus all of the light at a single point inside the camera, on the sensor. However, because all the different colours are coming through the lens in different ways, it is very difficult to precisely focus all the colours at the same point and what tends to happen is that some of the light is actually focused a little bit behind the sensor and some of it a little bit in front. This means that those colours (wavelengths) that are not precisely focused are a little bit blurry and this is what we see as chromatic aberration, or colour fringing.
In the picture of the tree at the top of this article, which clearly has a lot of blue fringing, the blue light coming through the lens is not being focused correctly and this is what has led to the chromatic aberration we can see.
All lenses suffer from this problem to one degree or another. However, more expensive lenses have additional glass elements built in to specifically correct this problem, so more expensive lenses tend to suffer less from chromatic aberration than cheaper ones. However, because it’s a problem with almost every lens to some degree, post-processing software often has corrections built in and merely checking a box can often remove the worst of it.
As I said above, bad colour fringing is most apparent in an image with strong contrast – dark objects against bright backgrounds or vice versa. The best way to minimise this in your pictures is to experiment with your camera. Deliberately try to create chromatic aberration in your images so that you know what situations make it really apparent and what fringing occurs – sometimes it will be blue like in the picture above, sometimes it will be yellow, sometimes it will be violet and sometimes it will be a combination of colours. If you know when and how it occurs with your camera, then you know what situations to avoid and if it can’t be avoided, then at least you should know that some software can take care of it for you in post production. It is worth bearing in mind however, that if you are printing a picture at a normal size, or uploading to social media it's very likely no one will ever see the colour fringing so before you go to great lengths to fix or avoid, have a think about the picture's final use.
Now, and in very, very, simple terms all of these wavelengths (colours) move in different ways through a big chunk of glass like a prism, or indeed, a camera lens. Blue light is very energetic and has a short wavelength. Red light is less energetic and has a longer wavelength. Green light is somewhere in the middle. As all these colours, with different energy, pass through the camera lens, they are bent, or refracted, in different ways. Blue light, with all its energy, bends more than red light. The whole purpose of the lens is to focus all of the light at a single point inside the camera, on the sensor. However, because all the different colours are coming through the lens in different ways, it is very difficult to precisely focus all the colours at the same point and what tends to happen is that some of the light is actually focused a little bit behind the sensor and some of it a little bit in front. This means that those colours (wavelengths) that are not precisely focused are a little bit blurry and this is what we see as chromatic aberration, or colour fringing.
In the picture of the tree at the top of this article, which clearly has a lot of blue fringing, the blue light coming through the lens is not being focused correctly and this is what has led to the chromatic aberration we can see.
All lenses suffer from this problem to one degree or another. However, more expensive lenses have additional glass elements built in to specifically correct this problem, so more expensive lenses tend to suffer less from chromatic aberration than cheaper ones. However, because it’s a problem with almost every lens to some degree, post-processing software often has corrections built in and merely checking a box can often remove the worst of it.
As I said above, bad colour fringing is most apparent in an image with strong contrast – dark objects against bright backgrounds or vice versa. The best way to minimise this in your pictures is to experiment with your camera. Deliberately try to create chromatic aberration in your images so that you know what situations make it really apparent and what fringing occurs – sometimes it will be blue like in the picture above, sometimes it will be yellow, sometimes it will be violet and sometimes it will be a combination of colours. If you know when and how it occurs with your camera, then you know what situations to avoid and if it can’t be avoided, then at least you should know that some software can take care of it for you in post production. It is worth bearing in mind however, that if you are printing a picture at a normal size, or uploading to social media it's very likely no one will ever see the colour fringing so before you go to great lengths to fix or avoid, have a think about the picture's final use.
