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This is technically known as a catadioptric lens and has an unusual construction of mirrors and lens elements. As well as glass elements there are mirrors at the front and rear to fold the light as it enters the lens. Although this results in a body that's a little wider than normal, advantages are: 1. The lens is usually only half the physical length a regular lens of the same focal length would be, and 2. It's much lighter. Disadvantages are: 1. There is no adjustable aperture, so the user is forced to take all of his photos at a permanent aperture setting, usually f8, but sometimes even f11, which means you need plenty of light for taking photos; 2. Practically all mirror lenses use manual focus; 3. Highlights that are out of focus are, in some situations, shown as doughnut shapes (although some actually like this characteristic and consider it an advantage, not a disadvantage).
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A lens that uses reflected and refracting surfaces to form an image. More commonly known as a mirror lens.
An SLR or single-lens reflex camera is really designed for the enthusiast or professional photographer, or for the person who can put up with a larger camera in return for increased accuracy and greater versatility. This type of camera has through the lens viewing with a mirror behind the lens and a pentaprism to direct the light passing through the lens to the optical finder. The mirror lifts up out of the way as a photograph is taken. As you look through the lens that takes the picture, the composition can be more accurate. And in most cases you can exchange the lenses, giving you a wider scope of options. The metering and focusing systems are usually more accurate too. Despite all this creativity it's still possible to put most SLRs in a full auto point & shoot mode so anyone could use one with ease, but don't expect to fit one in a pocket! They are much bigger than that. A modern, digital version of the SLR is called a DSLR.
Also known as a reverse or inverted telephoto, this lens design has a diverging lens element positioned in front of the aperture and a converging element positioned at the rear. This makes the distance from the rear of the lens to the focal plane longer than the lens focal length. Retrofocus design has been adopted in wide-angle lenses so the rear of the lens does not impede the movement of an SLR camera's reflex mirror.
A camera with two lenses the upper one is the viewfinder lens that has a mirror reflex view and the bottom one is the taking lens.
A multi sided glass prism housed in the roof of an single-lens reflex camera so that the image that's seen be the lens can be viewed through an optical viewfinder above the lens. The light enters through the lens is reflected up by a reflex mirror to the prism and across to the eye.
A lightbox that has a mirror and lens projection system built in so that the user can present data to groups using acetate sheets printed with data.