"If you whipped out a single-lens reflex camera the woman would probably get a bit antsy, but because it's a mobile phone, she'll often go along with it," says 33-year-old securities worker and hamedori practitioner to SPA! magazine.
The practice is called hamedori and a lot of women find it increases stimulation.
"It's sort of an extension of dirty talk. You can tease women by pointing the camera at them and watching her blush. That alone is fun," says 29-year-old construction worker but added that
"You've got to make sure you dump the footage after you've taken it, though," in case you're thinking of making a tidy profit out of it over the Internet.
But many practitioners of hamedori do save their amateur movie, a fourth of whom get a kick out of appearing in an amateur film while others keep them for less egotistical reasons.
"I want to use it to objectively analyze my technique," was how practitioner put it.