3 - Cyl, Mirrors Flashcards
Describe: stigmatic system
A point source produces a point image
Describe: astigmatic system
Characterized not by a single focal point, but by a pair of focal lines
-i.e. power is different along different meridians
Describe cylindrical lens meridians
The direction parallel to the axis of the cylinder is the AXIS meridian
The direction perpendicular to the axis meridian will be the POWER meridian
Collectively = PRINCIPAL meridians
Cylinder lenses always have __ along one meridian
Zero power
Describe spherical lenses
Rotationally symmetric
-the wavefront will be altered in a meridian-independent manner (i.e. power in each meridian is the same), therefore no need to specify orientation
Describe contraocular view
View that a doctor would have when looking at the patient:
- vertical meridian = 90 degrees
- horizontal meridian = 180 degrees
How to label/specify cylindrical lenses
1) specify location of axis with x
2) specify power in given meridian with @
Spherical equivalent power equation
Pse = (Fc/2) + Fs
Spherical equiv) = (cyl power/2) + (sphere power
Describe circle of least confusion/blur circle
Point of best focus for a lens
Located DIOPTRICALLY HALFWAY B/W THE 2 LINE IMAGES that are formed in the principal meridians
In a sense, we’re finding the point where the image is distorted equally in each meridian
When we use spherical equiv, we assure the COLC will fall on the retina
Describe interval of sturm
Distance bw the 2 foci of the principal meridians
LINEAR/SPATIAL DISTANCE b/w locations of the horiz and vert line formation
How we find power in an oblique meridian
Sine-squared rule
Sine-squared rule equation
Pα = Ps + Pc*sin^2(θ)
(Power in alpha meridian) = (sphere power) + (cyl power)*(sin squared theta)
Where: theta is the difference b/w meridian alpha and axis of cyl (= alpha - axis)
Tilted lenses effects
-pantoscopic tilt of a minus lens
Induces minus cyl x 180
Tilted lenses effects
-pantoscopic tilt of a plus lens
Induces minus cyl x 90
Equiv to plus x 180
Tilted lenses effects
-faceform tilt of a minus lens
Induces minus cyl x 90
