The big difference that rangefinder effective base length (EBL) will make is with fine focusing accuracy when depth of field is shallow. The RF will appear to be in focus, but due to the limited EBL the lens' focus will be off from the intended focus plane. You won't be able to notice a problem with pretty much any RF lens when DOF is not overly shallow (e.g. you'll never notice a problem at f/8). But when running wide-open apertures, especially at longer focal lengths, critical focusing may be off. Esp. lenses like the Noctilux 50/1, Summilux 75/1.4, and the Zeiss Ikon 85/2, require a good EBL at max aperture due to shallow DOF.
To make ElrodCod's point completely clear, it's worth noting that the EBL is the physical RF base length times the viewfinder magnification. As noted, the Bessa R2/R3/R4 physical baselengths are all the same, the only difference is in the VF magnification. The R4A/R4M cameras by design have a x0.52 magnification (i.e. wider) than the other Bessa's (e.g. compare to the x1.0 VF magnification in an R3M). The R4's tradeoff is reduced EBL since the magnification factor is relatively smaller.
Last edited by John W; 11-27-2008 at 01:42 PM. Click to view previous post history.
Reason: fix typo