The most popular type of general-purpose camera for enthusiasts and professionals is the single lens reflex (SLR).
This type of camera has a moveable mirror behind the lens which reflects an image through a five-sided prism (pentaprism) or pair of mirrors, onto a glass screen (the viewfinder). This means the photographer sees exactly the same image that will be exposed on the recording medium (film or digital CCD).
When you press the shutter button, the main mirror is flipped out of the way so the light passes straight through to the recording medium as pictured below. As you do this, you notice the image briefly disappear from the viewfinder. There is also the familiar sound of the "camera click" as the whole mechanism works.
The obvious advantage of this system is accuracy. If the image you see through the viewfinder is not exactly the same as the image on the recording medium (as in viewfinder cameras), the composition of the resulting photograph may be noticeably different to what you expected. The SLR camera makes sure this doesn't happen.
SLR cameras also work well with different lenses. Since you are seeing exactly what the lens sees, you can swap lenses as required and always be confident of what you are capturing.
There are also some disadvantages of this system:
- SLR cameras tend to be bulkier and heavier than viewfinder cameras.
- SLR cameras tend to be noisier than other types because of the physical mechanism. This isn't usually an issue but it can be a problem if you are trying to shoot discreetly (e.g. wildlife photography).
- SLR cameras are relatively complex so there is more chance of them breaking down.
These disadvantages do not normally present a major concern. For most people the SLR is an excellent choice for taking consistent high-quality photographs.