stop up (third-person singular simple present stops up, present participle stopping up, simple past and past participle stopped up)
- To fill a hole or cavity, or block an opening or passage, as with a plug.
- 1885, Mark Twain, Huckleberry Finn, ch. 37:
- So then we […] scratched around and found an old tin washpan, and stopped up the holes as well as we could.
- (photography) 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.
- 2002, Kathleen Tracy, The Complete Idiot's Guide to Portrait Photography, →ISBN, p. 18:
- To stop down means to narrow the aperture; to stop up or open up means to expand it.
- (increase the aperture of a photographic lens): stop down