In our last post, we looked at how aberrations are the root cause of the use of multiple lenses in constructing a complete camera lens. Today, and over the course of future posts, let us consider in more detail the concept of aberration.
Most generally, aberration refers to the distortion of an image when passed through an optical system, such as digital camera lenses. Limitations of the system might lead to blurring. A common misconception about aberrations, however, is that they are caused by imperfections in the device or system. Rather, the real root cause of aberrations is in fact in the relatively simplistic and, therefore somewhat inaccurate, boundaries set by paraxial theory--that theory around which optical systems are built. To put it more succinctly, even lenses built perfectly to the specifications of paraxial theory will experience aberrations because the theory does not perfectly describe the behavior of light in such systems.
Aberrations can be broken down into two major categories. Those derived from geometrical structure and those derived from the effects on wavelength due to dispersion. Though shape and material are important to both categories, the shape will obviously play a larger role in the former, causing blurring, and material/density will play a larger role in the latter, causing shifts in coloration in addition to blurring. Geometrically derived aberrations are called monochromatic because they affect even monochromatic light, whereas dispersion-based aberrations are called chromatic because they are only evident in situations with multiple color variants.
Digital camera lenses correct for these aberrations and multiple subcategories therein. Soon, we will take a look at some of the ideas underlying the most common chromatic and monochromatic aberrations.