Archived posting to the Leica Users Group, 2009/09/08
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]I am not sure it is as much as that in most cases! In SLRs with non-changeable screens the split image wedges and or microprisms are angled at equivalent of f5.6 so that all lenses available for the camera will be able to be focussed using these aids. Some interchangeable screen models have "fast lens" screens available where the prisms are angled to look out of a f4 aperture. This means the effective rangefinder base of a normal slr using a 50mm lens is about 9mm! This means that the shortest lens for an SLR having the focussing precision of a 47mm base rangefinder (M9) in its split image spot or microprisms is 47x5.6= 263mm!! Experience tells that SLRs focus fine, so either the M base is way more than needed, or the limit in focus precision is in the mechanical precision of the linkage for the rangefinder mechanism. It is automatically easier to get this precision on an SLR where there is a single optical element (the lens) and the rangefinder prisms are adjacent on the same part. The screen location precision is still important, of course. Frank On 8 Sep, 2009, at 18:53, lrzeitlin at aol.com wrote: > . Accuracy of the split image RF is what makes its use possible in > SLRs where the base length is only the diameter of the lens used.