focuser

noun

1. A device on a telescope or other optical instrument that moves the lens or eyepiece to make the image sharp.

   C2

   countabletechnical

   • "Turn the focuser slowly until the stars look sharp."B2
   • "The telescope's focuser allows precise adjustment of the eyepiece position."C1
   • "A dual-speed focuser makes fine focusing easier when you view planets at high power."C1
   • "The camera's focuser struggled to track the moving subject."C1

2. A person who focuses attention or keeps something centered on a goal.

   C2

   countablerare

   • "She acted as the focuser for the discussion."B1
   • "A skilled focuser can steer a long debate back to its central purpose."C1