<P> As camera a lens technology developed and wide aperture lenses became more common, rangefinder cameras were introduced to make focusing more precise . Early rangefinders had two separate viewfinder windows, one of which is linked to the focusing mechanisms and moved right or left as the focusing ring is turned . The two separate images are brought together on a ground glass viewing screen . When vertical lines in the object being photographed meet exactly in the combined image, the object is in focus . A normal composition viewfinder is also provided . Later the viewfinder and rangefinder were combined . Many rangefinder cameras had interchangeable lenses, each lens requiring its own range - and viewfinder linkages . </P> <P> Rangefinder cameras were produced in half - and full - frame 35 mm and rollfilm (medium format). </P> <P> After exposure every photograph is taken through pinch rollers inside of the instant camera . Thereby the developer paste contained in the paper' sandwich' distributes on the image . After a minute, the cover sheet just needs to be removed and one gets a single original positive image with a fixed format . With some systems it was also possible to create an instant image negative, from which then could be made copies in the photo lab . The ultimate development was the SX - 70 system of Polaroid, in which a row of ten shots - engine driven - could be made without having to remove any cover sheets from the picture . There were instant cameras for a variety of formats, as well as cartridges with instant film for normal system cameras . </P> <P> In the single - lens reflex camera, the photographer sees the scene through the camera lens . This avoids the problem of parallax which occurs when the viewfinder or viewing lens is separated from the taking lens . Single - lens reflex cameras have been made in several formats including sheet film 5x7" and 4x5 ", roll film 220 / 120 taking 8, 10, 12 or 16 photographs on a 120 roll and twice that number of a 220 film . These correspond to 6x9, 6x7, 6x6 and 6x4. 5 respectively (all dimensions in cm). Notable manufacturers of large format and roll film SLR cameras include Bronica, Graflex, Hasselblad, Mamiya, and Pentax . However the most common format of SLR cameras has been 35 mm and subsequently the migration to digital SLR cameras, using almost identical sized bodies and sometimes using the same lens systems . </P>

1. what are the advantages of using a traditional film camera a digital camera