What makes a lens good?

What makes a good lens can be argued on a scientific basis or according to aesthetic considerations. Most people want a lens that produces a tack-sharp image with great color rendition for superior image quality. Certainly, how the lens handles mechanically is also important; it has to function as the photographer’s instrument and be able to be “played” without disrupting the creative process with limited functionality.

Canon outlines six primary characteristics of an ideal lens:

  • Complete photographic quality. Truly great lenses feature both superior resolution as well as contrast across their entire surfaces. By using a more-than-sufficient amount of high-quality glass and optical coatings backed by sophisticated technology and engineering, resolution and contrast (which often work against each other) are optimized.
  • Consistent color reproduction among all lenses. A primary goal of Canon optical engineering is consistency and uniformity of color reproduction no matter which interchangeable lens is being used.
  • Out-of-focus quality. For photographers, what’s out of focus is often as important as what’s in focus. This natural “blur” effect using narrow depth-of-field is critical to representing a three-dimensional subject in a two-dimensional image, so it has to look believable and natural — which is yet another factor that’s part of lens design and engineering.
  • Ergonomic functionality. A lens needs to be comfortable, functional, and easy to use. While an attractive design is nice to have, cameras and lenses need to follow a function-before-form rule of industrial design. Canon EF lenses are built to provide sensitive, smooth manual focus and zoom functions, as well as accessible and logically positioned and intuitively operated features and functions.
  • Quiet functioning. dSLR cameras are notoriously noisy, with so much mechanical operation. This has diminished steadily, first because of solid-state electronic operation (instead of levers and gears) and second because of increased precision engineering of components as well as innovative technologies such as USM. This has enabled very quiet autofocusing as well as other camera and lens operations.
  • Reliability. Being completely portable, cameras must endure a variety of rigorous conditions, such as weather, vibration and shocks, dirt and dust, and other factors, and keep operating precisely and producing high-quality images. Canon cameras are tested extensively in many situations and are subjected to many types of physical torment before they are rated for different types of use.

Category: Science of Lenses

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