Steve Thorp explains on his website
www.stevethorp.co.uk/index.php?option=com_content&task=view&id=312&Itemid=38
Footage herehttp://video.mpora.com/watch/1Q8b7HoXs/
Great angle although the wide angle lens slightly makes the rider's head disproportionately large. Initially thought it made the sail look really small too but on closer inspection I think it is looking at the boom length.
I think these tail cams give the best possible perspective, at least with the go-pro's. Its certainly a much better angle than the boom or mast cam.
this one could possibly do with being bent back a bit, so the cams more behind the head rather than above it. Sort of like your standing behind the sailor watching their every move.
Here is a longer flat water tail cam for those who haven't seen it, probably a bit to long/bulky for waves. Steve Thorpes is much lighter/compact and more suitable for waves & jumping.
I developed mine for a full view of the board and sail with smooth footage capture. Here is the initial test run and thread on the GPS forum.
www.seabreeze.com.au/forums/Windsurfing/Gps/Tail-Cam-Test-Run/