Pros and Cons
The viewfinder of a rangefinder camera is necessarily offset from the taking lens, so that the image shown is not exactly what will be recorded on the film; this parallax error is negligible at large subject distances, but increases as the distance decreases. More advanced rangefinder cameras project into the viewfinder a brightline frame that moves as the lens is focused, correcting parallax error down to the minimum distance at which the rangefinder functions. The angle of view of a given lens also changes with distance, and the brightline frames in the finders of a few cameras automatically adjust for this as well. For extreme close-up photography, the rangefinder camera is awkward to use, as the viewfinder no longer points at the subject.
In contrast, the viewfinder pathway of an SLR transmits an image directly "through the lens". This eliminates parallax errors at any subject distance, thus allowing for macro photography. It also removes the need to have separate viewfinders for different lens focal lengths. In particular, this allows for extreme telephoto lenses which would otherwise be very hard to focus and compose with a rangefinder. Furthermore, the through-the-lens view allows the viewfinder to directly display the depth of field for a given aperture, which is not possible with a rangefinder design. To compensate for this, rangefinder users often use zone focusing, which is especially applicable to the rapid-fire approach to street photography.
The rangefinder design does not lend itself to zoom lenses, which have a constantly-variable field of view. The only true zoom lens for rangefinder cameras is the Contax G2 Carl Zeiss 35–70mm Vario-Sonnar T* Lens with built-in zoom viewfinder. Very few lenses, such as the Konica M-Hexanon Dual or Leica Tri-Elmar, let the user select among two or three focal lengths; the viewfinder must be designed to work with all focal lengths of any lens used. On a technical level, the rangefinder may become misaligned, leading to incorrect focusing, a problem absent from SLRs.
Nonetheless rangefinder cameras have advantages over SLRs for certain applications. Since there is no moving mirror, as used in SLRs, there is no momentary blackout of the subject being photographed. The camera is therefore often quieter, particularly with leaf shutters, and usually smaller and less obtrusive. These qualities make rangefinders more attractive for theater photography, some portrait photography, action-grabbing candid shots and street photography, and any demanding application where portability matters. The lack of a mirror allows the rear element of lenses to project deep into the camera body, making high-quality wide-angle lenses easier to design. The Voigtländer 12mm lens was the widest-angle rectilinear lens in general production for a long time, with a 121 degree angle of view; only recently have comparable SLR lenses entered the market.
Rangefinder viewfinders also usually have a greater field of view than the lens in use. This allows the photographer to be able to see what is going on outside of the frame, and therefore better anticipate action. In addition, with viewfinders with magnifications larger than 0.8x (e.g. some Leica cameras, the Epson RD-1/s, Canon 7, Nikon S, and in particular the Voigtländer Bessa R3A and R3M with their 1:1 magnification), photographers can keep both eyes open and effectively see a floating viewfinder frame superimposed on their real world view. This kind of two-eyed viewing is also possible with an SLR, using a lens focal length that results in a net viewfinder magnification close to 1.0 (usually a focal length slightly longer than a normal lens); use of a much different focal length would result in a viewfinder with a different magnification than the open eye, making fusion of the images impossible.
If filters that absorb much light or change the colour of the image are used, it is difficult to compose, view, and focus on an SLR, but the image through a rangefinder viewfinder is unaffected. On the other hand some filters, such as graduated filters and polarizers, are best used with SLRs as the effects they create need to be viewed directly.
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