Voightlander Bessa lenses question

[drmabus]

According to the descriptions of the 25/4 lenses, the screw mount lens is not rangefinder coupled but the 25/4 P is. Besides the different mounts, what is the difference between a lens that is rangefinder coupled and one that is not? Are there important or significant advantages in coupling?

 

[Jamie Pillers]

With a "coupled" lens, you can use the in-camera rangefinder/viewfinder window to focus... like when you focus an SLR. With non-coupled lens, you can use the rangefinder/viewfinder window to frame the image, but not to focus. For these lenses, you have to use the scale numbers on the lens body to estimate the distance to your subject. But with wide-angle lenses like the 25mm, you don't have to be too concerned about your distance estimation skill because of the lens' significant depth of field characteristics.

 

[drewbarb]

A coupled lens mates to the RF of a camera so that focus can be set with the mechanics of the rangefinder. An un-coupled lens won't; instead, focus distance is set by guessing, probably using scale- or hyper-focusing. This works fine with wide angles like the 25mm, since D.O.F. is so wide.