If I had a x1 teleconverter (although it wouldn't be a teleconverter at x1) I could leave it on and change lenses and not get dust on the sensor.
Is it possible to put a good quality piece of plain glass in the thinest converter body and leave it on the camera? I am guessing that the focal length must change (bit like bellows?) but by how much? would a 10mm become a 12mm or 30mm?
Is this a brilliant idea
or the start of an urban myth?