In an SLR, the apparent magnification depends on the lenses between the prism and your eyes (viewfinder magnification) as well as the objective lens' focal length; for a given viewfinder magnification, you will obtain a 1:1 view at some objective particular focal length. You can get a magnifying eyecup that clips over the back of the prism and gives you (typically 1.4x) greater magnification - I have the Pentax version installed on my Sony DSLR that makes manual focusing a little easier though of course at the cost of a dimmer image.
There are plenty of SLRs with 100% viewfinder coverage; it's just that they're a bit annoying to build because it requires an oversize mirror; there is nothing special about the mirror that means you need to have a reduced view. A bunch of Nikon Fs, as well as Minolta 9 and Sony A900.
Gosh folks are mixing up issues! There are two characteristics about viewfinder size:
1. amount of area of the frame of the camera a.k.a. 'viewfinder area', such as 97%
2. magnification presentation thru the eyepiece, e.g. 0.92x.
The Olympus OM-1 showed 97% of the frame, the Nikon F and F4 showed 100%.
The Olympus OM-1 showed the viewfinder at 0.92x magnification (with 50mm lens), the OM-4 showed 0.84x magnification, and the Nikon F4 showed 0.7x magnification.
The reason for the shrinkage in viewfinder magnification (even while showing 100% of the frame area) was the need to cram in all of the camera status displays in the viewfinder area surrounding the focusing screen area!
If manufacturers tried to retain the magnification factor, the pentaprism housing would have grown larger in size to accommodate the larger pentaprism needed to view the 24x36mm focusing screen and the area surrounding it which housed the status displays, increasing cost and price and bulk and weight of the camera.
Last edited by wiltw; 10-23-2011 at 01:02 AM. Click to view previous post history.
Simple cost, size, and weight reduction. 75% + of the people can`t see the difference anyway. When they want to get real cheap, they use mirrors instead of a prism.
If you look at my D3 & D700, the D3 has 1:1 and it has an obviously larger pentaprism to accomodate. Same with my F2 ( 1:1) and FE2.
Katz eye can not make a focus screen for the D3 because it is slightly larger than than the D700 which is the size limit blank they can make. The D3 and D700 are both full frame digi cameras for those who do not know.