- All pressure gradient microphones have proximity effect, not only condensers (unless we get into "variable-D" microphones which no one here is using TTBMK).
- "Free field" effectively means direct and anechoic rather than any particular measuring distance. It's "free" in the sense of "unobstructed", with room boundaries considered as obstructions if any sound bounces off of them and then reaches the microphone indirectly.
- The DIN/IEC standard refers to "plane wave" conditions, which would mean that no proximity effect should be included at all. But nothing in the real world generates true plane waves, so the effect can only be approximated. Proximity effect trails off gradually as you get farther away from the sound source, though, and typically is still evident at 1 meter, assuming a point source or the like. To reduce it to where it's negligible, you would generally need a greater distance, depending on the geometry of the capsule. This is particularly true for supercardioid or figure-8 patterns, where the effect is greater than for an equivalent cardioid, and for larger microphones in general.
The thing is, I know of no manufacturer that follows this rule to the letter. Neumann, Schoeps, Sennheiser, I believe AKG when they still existed, and many/most other European manufacturers of studio microphones as well as some in other countries, generally have used a 1-meter (or calculated equivalent) measurement distance. They do it because they have always done it and because the others are doing it and they don't want to be the only one that looks bad.
Nowadays some manufacturers specify different models differently, depending on the intended application. Microphones designed for very close miking might be measured at 15 or 30 cm (about 6 or 12 inches). This makes the graphs easier to interpret for people who really use microphones at such distances. But such graphs are difficult to interpret for other miking distances, and can deceive those who don't understand the issue, or who set their concern aside out of sheer enthusiasm when they see a bright, shiny object that they want to own. (Of course that could never happen here ...)
Even if you know what measurement distance was used (which the manufacturers don't often tell you), there's no set formula for converting a 15 or 30 cm curve to a 1-meter curve. It depends, as I said, on the acoustical design and physical dimensions of the capsule. So I'm always glad when a manufacturer indicates the low-frequency response at various distances.
--best regards
