A good shot, Wim - may I ask about the tech. / circumstance details as I've also recently taken some 'bubble blowing ' pics, which are very poor relations to yours ...
The images was cropped. It is about 35 percent of the original. With a 150 mm Sigma macro lens. Camera is a Nikon D2X ( I never dare to tell this because it is a bit of a 'big' camera for a poor artist like me:-)
It was made against the sun, flash on minus 1 to fill in the shadows. 1/250th of a second, aperture 8, hand held. It is still a bit blurred. If I would have used a tripod or monopod it would have been better!