Lens testing: focus distance

[nsecomb]

Apologies to any who think this a silly question; feel free to have a laugh.

To those of a technical bent:
- I'm about to do a basic lens test at home, for the first time, using a set of targets and instructions from some helpful websites, just to make sure that the lens isn't a lemon before the 7 day return period expires.
- While I do think that new camera's focusing sensors will be able to get the focus distance more correct than I could by eye, I'd like to rule out incorrect focus as an explanation for any bluriness (and discover thats an issue with the camera if it is).
- I intend to set the camera up on a tripod at a controlled (tape measured) distance from the target, but where do I take the distance measurement to on the camera?  Is "focus distance" the distance from the target to:
a) sensor plane within the body? or
 mid point of lens? or
c) front of lens?

Thankyou in advance for advice.

regards,

Nigel

[Panopeeper]

The distance is theoretically from the first nodal point, which is inside the lense. somewhere, depending on the design.

However, I can't fathom, what on earth you want to use this for. When testing focusing to infinity, will you walk up to the moon and measure the distance?

This is a totally irrelevant measurement. The markings on the barrel are only approximate, for orientation. Furthermore, the "camera's sensor" has no idea of the focusing distance. Some cameras report this distance, but they receive it from the lens.