One of the most commonly touted features in lens design are aspherical elements, though you might wonder just what that rather technical-sounding name refers to. This excellent video will give you an introduction to aspherical elements, including what they are, how they function, and why they are so highly desired by photographers.
Coming to you from Michael The Maven, this great video will give you an introduction to aspherical lens elements. If you look at the manufacturer's description for many modern lenses, one of the main features they will tend to brag about are aspherical elements. Aspherical elements tend to be more complex than a simple spherical lens, and thus, they tend to be more expensive to produce, but the benefits include things such as reducing spherical aberrations and astigmatism and reducing weight and size by replacing a more complicated lens group. In turn, despite being more expensive to produce than a standard spherical element, they can sometimes actually bring the overall cost of the lens down, as they simplify the design. They are by far one of the most important features of modern lens design, and they enable higher quality images and smaller and lighter lenses. Check out the video above for the full rundown.