Notes

A camera is an optical instrument for recording images, which may be stored locally, transmitted to another location, or both. The images may be individual still photographs or sequences of images constituting videos or movies. The word camera comes from camera obscura, which means "dark chamber" and is the Latin name of the original device for projecting an image of external reality onto a flat surface. The modern photographic camera evolved from the camera obscura. The functioning of the camera is very similar to the functioning of the human eye.

Types of Camera
SLR (Single Lens Reflex): The viewfinder sees the same image as the main lens, i.e. what you see is what you get. SLRs also allow you to change lenses for different purposes. This is a hugely popular type of camera, pretty much the standard for enthusiasts and professionals.
Viewfinder (or range finder): In this type of camera the viewfinder is separate to the lens. This is common in cheap cameras, although some professional cameras also use this configuration. The main problem with a separate viewfinder is that the image you see may not be quite the same as the image that gets recorded. This limitation is overcome in professional cameras by using viewfinders that compensate for the different positions. Viewfinder cameras do have some advantages; for example, lower noise and higher light levels to the viewfinder.
Twin reflex: The camera has two lenses — one for the photograph and one for the viewfinder. This type of camera has certain advantages in some professional situations.
View: A flexible bellows joins two standards — one with the lens and the other with the viewfinder or film. This allows for unusual types of composition; for example, distorting the shape of the image by skewing the film plane.
Pinhole: A very simple camera without a lens.