stop up

verb

1. To fill a hole or cavity, or block (an opening or passage), as with a plug.

   “So then we […] scratched around and found an old tin washpan, and stopped up the holes as well as we could.”

2. To permanently close or block (a road or path); to legally extinguish a right of way.
3. To increase the aperture of a photographic lens, moving from an f/stop represented by a higher number to an f/stop represented by a lower number and causing more light to pass into the camera.

   “To stop down means to narrow the aperture; to stop up or open up means to expand it.”