Not all lenses are equal. Some of them can cause problems for your photography. Spherical aberration is just one aspect you need to be aware of when it comes to using different lenses.
Knowing about what spherical aberration is means that you will have an easier time spotting it.
What Is an Aberration in Photography?
The definition of an Aberration is a departure from what is normal, usual, or expected, typically an unwelcome one.
These are things that happen to your images when you shoot, that you really do not want.
We already covered What Is Chromatic Aberration and How To Correct It in another article. Today we’ll tackle spherical aberration.
What Is Spherical Aberration?
Spherical aberration is an optical problem. it occurs when all incoming light rays focus at different points. This is after they pass through a spherical surface within the lens.
Light rays that pass through a lens near its horizontal axis refract less compared to rays that pass closer to the edge. This results in the light rays ending up at different spots across the optical axis.
In other words, the parallel light rays do not converge at the same point.
This reduces the focal strength as the image’s resolution and clarity are affected.
As you can see from the image above, the light rays refract or change their angle after passing through the lens. The light rays farthest from the center converge at a shorter distance along the optical axis (red and black line).
The light rays closer to the optical axis converge at a longer distance. This creates different focal points along the same axis.
There are three things that cause spherical aberrations. Lens design, quality of glass material used in the lens and even the placement of elements within the lens housing.
Lenses that are made from poor quality materials and large bubbles can mightily impact light reflection.
To have every light ray converge at a single focal point, you need a perfect lens.
Specialized and precise methods exist that lens manufacturers use to reduce the effect of spherical aberration.
How to Reduce Spherical Aberration?
With modern lenses, different techniques are used to reduce spherical aberration. One of these methods is to use an aspherical or non-spherical lens surface.
This lens curves outwards on one side. This is for the sole purpose of converging the light rays into a single focal point. You can see the effect in the image below.
Spherical aberration is more noticeable when the aperture of the lens is at its maximum. Opening it up by even one stop can reduce this aberration drastically.
This is because the aperture blades block the outer edges of spherical lenses.