From the Hasselblad Lens Catalog:
"Makro-Planar CF f/4 120mm:
Te designation "Makro" reveals that this lens possses an optimum image correction at close range. It is a lens to be recommended when maximum corner-to-corner quality is demanded in close-up work, especially when photographing flat copy, where high contrast is also a requirement.
This lens consists of 6 elements in four groups arranged around almost symmetrically to the iris diaphram. The Makro-Planar lens perfroms best in the region of slightly reduced imaging of the subject.
The shortest focusing distance of 0.8 m (reproduction ratio of 1:4.5) can be set using the helical focusing mount. By inserting the Hasselblad extension tube 32 the macro range can be increased to 1:2."
This lens is "optimized" that is, designed with a specific parameter in mind: Close-up photography. It *will* focus to infinity, and I *doubt* (a bunch!!) that Zeiss would allow it to go that far if it was a significant "failure" at that distance.
The 135 is a different animal:
"Makro-Planar CF f/5.6 135mm:
The 135 Makro-Planar f/5.6 lens has no focusing ring and is designed for use with a bellows extension or a variable extension tube.
With the bellows, the focusing range of the lens is contiuous from infinity down to 1:1; lifesize magnification.
Like the 120 mm Makro-Planar lens the 135 mm is optimally corrected for close-up work, but it is also an excellent lens for general photography where maximum image quality and freedom from distortion are required."
Can the run-of-the-mill 80mm Planar be used "satisfactorily" with bellows, tubes. or "Proxar" close-up Lenses? Uh... it depends on the individual's requirements - but it is "satifactory" enough for me.