If I remember correctly somewhere around 1/2in. give or take an 1/8in. I read some great reviews (not sure where) that the Pentax was the way togo. Got mine on EBay for about $80 from Australia.
Very interesting image. I think this is actually the first I see with a reversed 50mm lens. I think I may try to get one and screw it to my lensmate. How far away from the fly where you?
