Just some more info for those interessted.
The lenses are little optical gems. They have preset-levers so you can rapidly open them up for focusing (of course all viewing while shooting is done at working aperture, thus the absolute requirement for the eye hood)
The shortest one is 5.5mm retrofocus and the longest is 35mm. The short one is like a 40mm lens on a 35mm camera.
Bolex has an unusual shutter angle, and that, coupled with the light loss from the full-time viewing prism can lead to errors in exposure estimation. The Gossen/Bolex meter takes care of everything. I use a zinc battery in it.
Due to the magnification of the viewfinder image, the center lens (12mm) has the effect of being a "normal" lens (ie both your eyes open, the images are similar size). Compared to still photography, it is a long lens, approximating a 75mm lens on a 35mm camera. So, in effect the "normal" lens is what a still photographer may call a " portrait " lens.