There are some top-end pro cameras costing tens of thousands of pounds which can take better pictures, but frankly if you’re considering one of those then you’re reading the wrong book.
The acronym “SLR” stands for “single lens reflex”. The “single lens” part is to differentiate them from the twin-lens cameras that were popular in the 1960s, while the “reflex” part refers to the reflex mirror, an angled movable mirror that sits in front of the sensor and directs incoming light to the camera’s viewfinder. The mirror moves out of the way when a picture is taken, making that distinctive “click-clack” noise.
The very top professional DSLRs such as the Canon EOS-1DX Mark II still cost thousands, but then we’ve all got to have something to aspire to, haven’t we?
What goes on at the front of a Canon DSLR?
1 Reflex mirror
The reflex mirror is what gives the SingleLens Reflex (SLR) camera its name. Light coming in via the lens is split by this mirror, with most going upwards into the viewfinder, while a smaller proportion is allowed through a central part-silvered area and directed to the autofocus system. The reflex mirror flips up out of the light path when the shutter is triggered, producing that distinctive “clickclack” sound that all SLRs make.
This is the picture-taking element at the heart of the camera. It consists of a wafer of silicon embedded with millions of tiny photocells that produce electrical charge when exposed to light. The sensor in this Canon EOS 5D Mk II measures 36 x 24mm (the same as a frame of 35mm film) and has 21,100,000 individual photocells.
3 Image processor
The electronic circuitry inside the camera takes the individual charge signals from the photocells on the sensor and converts them into a digital image. Modern advanced processors such as the Canon DIGIC 4 in this EOS 5D Mk II are amazingly fast, and also apply sophisticated noise reduction algorithms.
4 Focusing screen
This consists of a ground-glass screen onto which the image seen by the lens is reflected via the reflex mirror. On advanced DSLRs such as this EOS 5D Mk II the focusing screen can be changed for one with grid lines or targeting reticules for specialist applications such as forensic or architectural photography.
This takes the light from the focusing screen and bends it through 90 degrees, directing it into the viewfinder eyepiece. Some cameras have a mirror in this position instead. It is the position of the pentaprism that gives SLRs their distinctive shape.
The defining characteristic of an SLR camera is an optical viewfinder that shows the view through the lens (TTL). Data such as focus points and exposure information are also shown in the viewfinder on a separate LED display. Optical viewfinders are generally considered to be superior to electronic ones.
7 Autofocus mirror
An area in the middle of the reflex mirror is partially transparent, allowing some light through onto a second mirror. This directs some of the incoming light downwards onto the autofocus sensor. This mirror also folds up out of the way when a shot is taken.
8 Autofocus sensor
Some of the light coming in via the lens is directed onto the autofocus sensor. Digital SLRs use a type of autofocus called “phase detection”,
which is inherently better and faster than the “contrast detection” systems used in compact and super-zoom cameras.
9 Light meter system
Some of the light directed towards the viewfinder is diverted to the light metering system. Modern digital SLRs have sophisticated multi-point light meters that can rapidly analyse a scene and calculate the exposure setting.
Digital SLRs are powered by larger, higher-capacity batteries than most other types of camera. Since the monitor screen isn’t in constant use, this gives most DSLRs excellent battery duration, a vital feature if you are using the camera in a professional capacity.
Modern cameras have a wide range of connectivity options. This Canon EOS 5D Mk II features USB 2.0 and HDMI as well as a dedicated composite video output connector, all hidden under a weatherproof rubber hatch.
12 IR remote sensor
Most digital SLRs have an optional infrared remote control for long-range shutter release, much more convenient than the old cable or bulb release gadgets.
13 Self-timer indicator
Even a pro camera like the 5D Mk II can be used for family shots. The LED indicator blinks to mark the countdown for a self timer shot.
14 Shutter button
Most digital SLRs incorporate a chunky handgrip, usually with the shutter button and adjustment wheel located on the top or front. As with compact cameras a halfpress of the shutter button activates the metering and AF systems. DSLR shutters are designed to be used hundreds of thousands of times.
15 External controls
Cameras intended for professional use are built to a more exacting standard, and incorporate weatherproof environmental seals on all the hatches and controls, keeping out dust and moisture.