Not all digital cameras have viewfinders. Digital cameras and smartphones have LCD screens for composing photos, and it’s only on higher end cameras that you get a viewfinder too.
But they are worth having. Sometimes it’s difficult to see an LCD display properly in the bright glare of daylight, and sometimes it just feels more natural to put the camera to your eye instead of holding it at arm’s length.
Viewfinders come in many different types, however. DSLRs use optical viewfinders that show a ‘naked eye’ view of the scene through the camera lens and projected on to a ground glass focusing screen in the camera’s pentaprism.
The pentaprism is a five-sided prism that rotates and flips the optical image so that it appears the right way round and the right way up in the viewfinder. Some cheaper DSLRs use a simpler ‘pentamirror’ system, but the effect is the same.
It is possible for light to get into the camera through the viewfinder eyepiece during long exposures, so some cameras have an eyepiece shutter or eyepiece cap to stop this happening.
Mirrorless cameras and compact cameras with viewfinders have a different design. Here, there is no optical viewfinder path; instead, the main sensor is used to capture a ‘live’ image and feed it either to the rear screen or an EVF (electronic viewfinder) that’s simply a tiny LCD display seen through a regular viewfinder eyepiece.
These cameras typically have an eye sensor to detect when you put the camera to your eye and will switch automatically from the rear screen to the viewfinder.
Optical viewfinders and EVFs share some specifications, including viewfinder coverage (100% is obviously the ideal, but some are 95%) and viewfinder magnification – the higher the magnification, the bigger the viewfinder image will be.
The viewfinder eyepiece is a lens which enables your eye to focus on the focusing screen or electronic display, and since different people have different eyesight characteristics, all but the cheapest cameras will have a viewfinder diopter adjustment for getting the viewfinder image into perfect focus.
There are other viewfinder types. DSLRs and mirrorless cameras offer ‘TTL’ (through the lens) viewing, where you see the scene directly through the camera lens.
This is not possible with all camera designs. In the past, many cameras used separate viewfinders mounted on the camera body near the lens but not showing the view through it. Some cameras still use these ‘direct vision’ viewfinders, including Leica with its classic M-series rangefinder cameras.
Direct vision viewfinders are very bright and clear, and they have the advantage that they also show what’s happening just outside the frame, which is very useful for fast-moving ‘documentary photography.
But they have disadvantages too. One is that they don’t cope well with different focal length lenses on interchangeable lens cameras. Manufacturers get round this by adding a series of brightline frames in the viewfinder to show the framing with different lenses attached.
The other problem is parallax error, where the framing of the camera becomes more and more different to the viewfinder’s when you get very close to your subject.Some more advanced cameras link the focus distance with a parallax correction mechanism to correct this.