I use a 2x converter on my Pentax 645 at times for tight head/faceshots (and for shooting wedding ceremonies from a balcony). Keep in mind that you'll lose a stop (1.4x) or two (2x) which makes critical focusing more difficult (exactly when it's most critical). Also, you'll be magnifying any weaknesses of the lens. With a high-quality, relatively-fast prime lens, the results are still quite good; with a cheap zoom, results may be marginal.(posted 8089 days ago)On the issue of getting in strangers faces, I'm not sure whether standing back with big, long zoom will actually make them feel more comfortable. I have better luck getting closer and being direct--when I don't act wary of them, they tend to respond in kind.
"He who does not trust enough will not be trusted." --Lao Tsu