1) Photography equipment
Found on
https://www.crosswordclues.com/clue/waterhouse-stop
The Waterhouse stop or Waterhouse diaphragm is an interchangeable diaphragm with an aperture (hole) for controlling the entry of light into a camera. A thin piece of metal (the diaphragm) is drilled with a hole (the aperture); a set of these with varying hole sizes makes up a set of Waterhouse stops, corresponding to what today we call f-stops or ...
Found on
http://en.wikipedia.org/wiki/Waterhouse_stop
No exact match found.
