Why do camera viewfinders rarely have a magnification of 1?

Viewfinder

The viewfinder of an SLR machine is generally a pentaprism viewfinder. Its function is to correct the upside-down image on the focusing screen so that the image seen through the viewfinder is the same as the direct one. The orientation of the scenery seen is exactly the same. This kind of viewfinder uses one lens for framing and photography, so there is no parallax and the framing is more accurate. The image after passing through the pentaprism is sent to the viewfinder eyepiece. The schematic diagram of light passing through a pentaprism and the shape of the pentaprism are shown in Figure 2-12(b).

The Olympus IS series AF SLR cameras have a built-in zoom lens. Because the body is relatively thick, they use a novel pentaprism viewfinder, the M-type viewfinder. The light path through the viewfinder must travel through an "M" shaped trajectory before reaching the viewfinder eyepiece. The overall effect is equivalent to that of a conventional pentaprism viewfinder, but it can greatly reduce the height of the fuselage.

The viewfinder has two main indicators: viewfinder magnification (referred to as viewfinder magnification) and viewfinder range.

Viewfinder magnification refers to the ratio of the eye angle of the subject observed through the viewfinder to the eye angle of the subject directly observed with the eyes, that is, the subject seen through the viewfinder The ratio between size and the size of the subject as seen directly with the eye. The magnification of the viewfinder is large, the visual angle is small, and the scenery seen during the viewfinder is close to the original object, with a strong sense of reality; the magnification of the viewfinder is small, the visual angle is large, and the panorama is easy to see when the viewfinder is used. If the magnification is too small, it will be difficult to observe the details of the object, which is not conducive to composition and focus, and the object image will be very different, making the viewfinder uncomfortable. Magnification is generally less than 1X, mostly between 0.75X and 0.95X.

Viewing range refers to the ratio of the range of scenery seen through the viewfinder to the range of scenery captured on film, expressed as a percentage. Generally, the picture seen in the viewfinder is not exactly the picture taken. It is always smaller than the picture taken, usually 90% to 100%. Only when the viewfinder reaches 100% can the viewfinder be called accurate. Currently, most of the cameras that can achieve 100% viewing range are professional SLRs.

There is also a type of viewfinder whose viewfinder eyepiece is designed according to the far sight point. The advantage of this viewfinder is that you can see the view clearly without putting your eyes close to the viewfinder, which is suitable for people who wear glasses. Some viewfinders also have a built-in diopter adjustment mechanism that can be adjusted according to each person's visual acuity. The diopter of a standard viewfinder is generally corrected to -1 diopter. If the diopter cannot be adjusted on the viewfinder, you can choose different diopter adjustment mirrors according to your own vision and install them on the viewfinder eyepiece. Camera manufacturers all produce such corrective lenses.

General amateur SLRs cannot replace the viewfinder, while many professional SLRs can replace the viewfinder. But among AF SLRs, only Nikon's F4 can replace the viewfinder. Users can choose different viewfinders according to the nature of photography. For example, when taking close-up or microscopic photography, choose the high-magnification viewfinder DW-21, which can magnify the image in the viewfinder field six times, making framing and focusing more accurate; when shooting at low angles, choose the flat-waisted viewfinder DW -20; when shooting underwater while wearing a mask, diving goggles or placing the camera in a sealed container, use the action viewfinder DA-20, etc.