A large proportion of photographers wears prescription glasses – I know, I’m one of them – and almost everybody wears sun glasses occasionally. But surprisingly, until high eye point or high eye relief viewfinders appeared – on the Nikon F3 HP in the early eighties, photographers with glasses could not see the integrality of the scene – let alone the aperture or speed information on the LED displays surrounding the view of the scene- without having to move their eye balls up and down and left to right.
As far as viewfinders are concerned, some cameras are better than others, though. The quality of the viewfinder of a manual focus camera is influenced by three factors:
Coverage: It’s the percentage of the image captured through the lens which is going to be shown in the viewfinder. 100% coverage is desirable – but expensive to manufacture, and only top of the line cameras (the real “pro” models) show the integrality of the scene in the viewfinder. Most SLRs show between 85% and 95% of the scene. Point and shoot cameras, (more precisely the few P&S which still have an optical viewfinder) are much worse. The best of them, the Canon G11 only shows 77% of the scene that will be captured through the eye piece.
Magnification: If the magnification was equal to 1, an object seen through the viewfinder would appear to be the same size as seen with the naked eye (with a 50mm lens on a 35mm camera). The photographer could even shoot with both eyes open. If the magnification ratio is lower than 1, then the object will appear smaller in the viewfinder than seen with the naked eye.
Magnification has an impact on composition and focusing. If the magnification ratio is very low (below 0.4) the image becomes so small that it’s difficult to compose the picture. Magnification is also a critical factor for picture sharpness on manual focus cameras: the accuracy of the focusing is directly related to what the photographer can see on the matte focusing screen, and the higher the magnification, the easier it’s going to be for him or her to focus accurately.