How does Nikon measure "minimum focus distance" for Macro/Micro lenses?

Question

This question is about Nikon SLR terminology. The answer could be different for non-SLR cameras, or for different maker.

The "minimum focusing distance" in the spec — it's measured and listed between what and the subject? Between sensor and the subject? Or between front of the lens and the subject? Or between back of the lens and the subject? At close distances and large lenses sizes, this makes big difference ...

The mystery comes from a review of the 60mm AF-S Micro Nikkor lens by Ken Rockwell. Ken is very trustful and thorough reviewer. In the "spec" section, Ken lists 18.5cm as "minimum focusing distance" (close focus)". No surprise, 18.5 cm is what appears in all published specs.

But Ken apparently owns this lens. Under title "Working distance" he pictures the Nikon and teddy bear, the subject, just several centimeters in front of the lens. He writes: "Nikon 60mm AF-S at closest focus distance... I measure only ... 48mm between the front of the lens and the subject at the closest focus distance"

Hmmm. It was 18.5 cm just several paragraphs above. Now it is 4.8 cm? Can anybody explain the discrepancy ? And answer my question at the beginning?

Answer 1

The answer is here, from Nikon:

Minimum Focus Distance

The minimum focus distance is the shortest distance at which a lens can focus. In the case of digital SLR cameras, the distance to the subject is measured from the focal plane mark on the camera body, not from the front of the lens.

Since the lens has a minimum focus distance of 18.5cm, and is 8.9cm long, and there's a 4.6cm flange to focal plane distance for the Nikon mount, that leaves about 5cm to spare, which is just about what Ken says (especially given that lens length is probably not measured exactly from the mounting flange on the lens).

It's also worth noting that this isn't Nikon specific — all lens minimum focus distances are specified in this way, although terminology may vary slightly. (Sony uses the same term as Nikon. Canon calls it "Closest Focusing Distance", and Pentax uses "Minimum Focusing Distance". Olympus and Panasonic are inconsistent, using "Closest Focusing Distance" in lens specifications but "minimum focusing distance" in articles.)