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Single-lens reflex camera

One lens for both viewing and taking the picture.


The Nikon F6 is a top example of a 35 mm Single Lens Reflex (SLR) film camera.
The Nikon F6 is a top example of a 35 mm Single Lens Reflex (SLR) film camera.

The advantage of the single-lens reflex (SLR) including the digital single-lens reflex camera (dSLR), is the photographer’s ability to view a scene through the camera lens itself (the same lens that takes the picture), enabling precise framing and viewing of the effects of focusing. This is known as TTL (through-the-lens) viewing.

IT’S DONE WITH A MIRROR AND A PRISM

The photographer using a dSLR or a 35mm SLR is actually seeing a reflected image that is corrected inside the camera to appear normal in the viewfinder. A mirror directly in the path of light that travels through the lens reflects the scene upwards to a viewing screen. A five-sided prism (or pentaprism - a solid block of optical quality glass) turns the reflected image the right way round for viewing through the camera’s eyepiece. The mirror, called a reflex mirror, moves out of the way, smoothly lifting, when a picture is taken – allowing the light to reach the film at the back of the camera – and then quickly moves back into place to enable TTL viewing again.

A medium-format SLR camera. You look down onto a ground glass screen to view the image.
A medium-format SLR camera. You look down onto a ground glass screen to view the image.

MEDIUM-FORMAT SLR CAMERAS

The same principle is invoked with medium-format SLRs – cameras that use larger-size roll film – except there is generally no pentaprism in these models, which means the image is seen as a mirror-image. You turn the camera left; the image goes right. It takes some getting used-to. (A prism attachment is available as an accessory for some makes, enabling eye-level viewing that is corrected to remove the mirror effect.)

The mirror directs the image from the lens directly to a viewing screen ("focusing screen") that the photographer looks at from above. Ambient light is blocked from the focusing screen by a focusing hood that folds away when the camera is not in use. A hinged, pop-up magnifying lens enables sharper focusing, but can be moved out of the way to aid in picture composition by allowing the photographer to see the overall screen. The image on the screen is a mirror image (reversed) that, as we said, some takes some getting used to, but soon becomes second nature to you.

The viewscreen is shielded from light by the pop-up sides of a folding focusing hood.
The viewscreen is shielded from light by the pop-up sides of a folding focusing hood.

WHAT YOU SEE IS WHAT YOU GET

The SLR camera eliminates the problem of parallax error that is common to twin-lens reflex and viewfinder cameras. Close-up pictures can be taken without fear of cutting off part of the image you see through the camera’s viewfinder. And, since the viewing system employs the lens itself, it works with virtually any lens fitted to the camera. Note that some super-telephoto lenses require the mirror to be maintained in the up position. Cameras for such lenses are equipped with a mirror lockup lever. Mirror lockup is also beneficial in reducing camera vibration to the minimum when performing photomicrography (taking pictures through a microscope).

DRAWBACKS OF THE SLR CAMERA

The mirrors in SLRs make noise when they move – some more than others. Camera manufacturers have been able to significantly reduce the amount of noise through effective sound-dampening design, but the loud click you hear from many cameras when the shutter is released is primarily caused by the mirror. This can be a disadvantage to the stealthy wildlife photographer whose silence in stalking animals is essential. Because it has no moving mirror, a quality viewfinder camera’s click can be almost inaudible, providing sufficient reason for some wildlife-stalking photographers to make it their camera of choice. Taking pictures silently is important for other photographers, too – for instance, when recording images during a live theater presentation or on an active television or movie production set, where any unusual noise might disrupt the performance or break the mood.

When your SLR is well-made by a reputable manufacturer, it has almost no drawbacks and many attractive and useful features.
When your SLR is well-made by a reputable manufacturer, it has almost no drawbacks and many attractive and useful features.

The components of the single-lens reflex camera’s pentaprism viewing system take up space, making the camera less compact. They also make the camera heavier than a similar viewfinder camera, and provide it with more parts to break down.

Under very low lighting conditions, precise focusing can sometimes be a problem because some light may be lost as it travels through the SLR’s complex viewing system.

Single-lens reflex cameras require the best workmanship and perfect mechanisms for minimum vibration or jarring when releasing the shutter. The focusing screen must be in accurate register with the focus of the lens on the film.

In spite of its drawbacks, the single-lens reflex camera (35mm and its dSLR equivalent) is the most versatile of camera designs, and has the most extensive range of lenses and accessories. Its advantages far outweigh its disadvantages. Note that many lenses designed for 35mm SLRs can be used on digital (dSLR) cameras. Click here for more information.

The choice of SLRs and dSLRs (digital single lens reflex cameras) available today is wider then ever, with camera makers introducing sophisticated, new models that have built-in microcomputers, tremendously fast shutter speeds (up to 1/8000 sec.), a choice of exposure reading modes, and many other features.

 
Further information...
Using 35mm SLR lenses on dSLR camera bodies