This is an interchangeable lens camera where you see an optical image in the viewfinder showing what the lens sees. They do this using a mirror inside the body that reflects the image seen by the lens up into the viewfinder. When you take a picture, the mirror flips up out of the way so that the image passes through the body to the sensor at the back of the camera. DSLRs work in the same way as SLR (single lens reflex) film cameras, but substitute a digital sensor for the film.
Digital SLRs (DSLRs)
The digital equivalent of the single lens reflex camera, where the image seen through the lens is reflected upwards by a mirror in the body and into the optical viewfinder. The mirror flips up and out of the way at the moment of exposure so that the image then passes through to the back of the camera and the shutter and sensor.
This is a key part of the optical viewfinder system of a digital SLR. It’s a five-sided prism inside a housing on top of the camera that reflects the image captured by the lens and formed on the camera’s focusing screen so that it’s the right way up and the right way round for viewing through the camera’s viewfinder eyepiece. Some cheaper DSLRs use a less expensive ‘pentamirror’ design instead. It costs less to make but does have a slight effect on the size and quality of the viewfinder image.
The percentage of the scene shown by the viewfinder. In better DSLRs you see 100% of the scene that will be captured, but in cheaper models it might only be 95-97%. That small difference can lead to objects showing at the edge of the frame that you hadn’t realised were there.
More advanced DSLRs have a secondary LCD display on the top so that you can check the main shooting settings without needing the rear screen. Status displays are black and white (or black on green) and usually have a backlight button for use in dark conditions.
An autofocus system that checks the position of objects from two angles. If they don’t line up the object is out of focus – and the system can use the difference to work out how far to refocus the lens and in which direction. Phase detection AF sensors are used on DSLRs and now phase detection pixels are built into some mirrorless camera sensors.