- A device which allows one to adjust the focus of an instrument such as a telescope.
- I decided to upgrade my telescope with a feather-touch focuser.
focus + -er
Variant of focus
nounpl. focuses or foci
- the point where rays of light, heat, etc. or waves of sound come together, or from which they spread or seem to spread; specif., the point where rays of light reflected by a mirror or refracted by a lens meet (called real focus) or the point where they would meet if prolonged backward through the lens or mirror (called virtual focus)
- focal length
- an adjustment of the focal length to make a clear image: to bring a camera into focus
- any center of activity, attention, etc.
- a part of the body where a disease process, as an infection, tumor, etc., is localized or most active
- the starting point of an earthquake
- either of the two fixed points used in determining an ellipse
- any analogous point for a parabola or hyperbola
Origin of focusModern Latin adopted in math. senses by Johannes Kepler (1604) ; from Classical Latin fireplace, hearth ; from uncertain or unknown; perhaps Indo-European base an unverified form bhok-, to flame, burn from source uncertain or unknown; perhaps Armenian bo, flame
transitive verbfocused or focussed, focusing or focussing
- to bring into focus
- to adjust the focal length of (the eye, a lens, etc.) in order to produce a clear image
- to fix or settle on one thing; concentrate: to focus one's attention on a question
- to meet at a focus
- to adjust one's eye or a lens so as to make a clear image
- to direct one's thoughts or efforts; concentrate
clear; distinct; sharply defined
out of focus