The next most important component of a digital SLR is the lens-or, more properly, lenses- because, unlike other types of digital cameras, the lens of a dSLR is interchangeable. Galileo and Leeuwenhoek came up with improved telescope and microscope gadgets, and most of the optical breakthroughs hence have involved different kinds of shapes of glass and other materials (including non-spherical “aspheric” elements) special coatings, and clever combinations of lenses to create zooms, fish-eyes, and other innovations.

Lenses consist of precision-crafted pieces of optical glass (or plastic or ceramic material) called elements, arranged into groups that are moved together to change the magnification or focus. Lenses contain an iris-like opening called a diaphragm that can be changed in size to admit more or less light to the sensor. Lenses are mounted in a housing that keeps the elements from rattling around and provides a way to move them to adjust focus and magnification. The lens housing can include a microprocessor, a tiny motor for adjusting focus (and, in non-dSLR cameras, for zooming), and perhaps a mechanism for neutralizing camera shake (called vibration reduction). You might find a switch or two for changing from autofocus to manual focus, locking a zoom lens so it doesn’t extend accidentally while the camera is being carried, and a macro lock/lockout button to limit the seeking range of your autofocus mechanism so your lens won’t seek focus from infinity to a few inches away every time you partially depress the shutter release.