Download Chief Ray Angle (CRA)

Armstrong Optical Ltd
31 Caxton House
Northampton Science Park
Kings Park Rd
Northampton, NN3 6LG
United Kingdom
Tel: +44 (0) 1604 654220
Fax: +44 (0) 1604 654221
Email: [email protected]
Web: www.armstrongoptical.co.uk
Chief Ray Angle (CRA)
Relevant for: ImageMaster®
A chief ray is the ray from an off-axis
object point which passes through the
center of the aperture stop of an optical
system. The chief ray enters the optical
system along a line directed towards the
midpoint of the entrance pupil, and
leaves the system along a line passing
through the center of the exit pupil. To
measure the angle between the optical
axis and the chief ray on the image side
the following method is used: The lens
under test is illuminated by the collimator
at different angles corresponding to the
object sided chief ray angles. The
detector head is moved to the image field
position at which the lens focuses the
image. Now the detector head is moved
towards the lens in small steps while the
software registers the lateral movement of
the focused spot. From these lateral
movements the CRA is calculated.
Measurement procedure of the Chief Ray Angle