Cardinal points

Cardinal points

1. CARDINAL POINTS AND VISUAL ANGLE AND AXES Presented by Akanksha kumari mandal Bsc Optometry (2 nd year) Abhaya college of Optometry(Banglore)

2. INTRODUCTION The analysis of an optical system using cardinal points is known as Gaussian optics, named after C F GAUSS. Knowing the location of the cardinal point to find out the image produced by an object passing through optical lens. Every optical system has 6 cardinal points : Focal points : primary and secondary. Principal points : primary and secondary . Nodal points : primary and secondary.

3. FOCAL POINTS Points at Which light rays arrive parallel to the optic axis are brought to a common focus on the optic axis. Primary Focal point (F) : It is also called object space. Secondaryy Focal point (F’) : It is called Image space.

4. PRINCIPAL POINTS Principal points are the point at the intersection of two imaginary rays , created by extending the ray entering the lens and extending ray exiting from the lens. The principal planes are the planes normal to the optic axis ,intersecting the principal points on the optical axis. Two principal planes : Primary principal plane. Secondary principal plane . ( 1 st = Object ) and ( 2 nd = image ).

5. NODAL POINTS The nodal point are two axial point , such that a ray , directed at the first nodal point will seen to emerge from the second nodal point parallel to its original direction. A ray directed to a nodal point at a certain angle , will exit the lens at the same angle.

6. SIGNIFICANCE Known cardinal point of an optical system - location and size of the image formed by the optical system.

7. AXES AND VISUAL ANGLES The eye has three principal axes and three visual angle. AXES OF THE EYE : OPTICAL AXIS . VISUAL AXIS . FIXATION AXIS .

8. AXES OPTIC AXIS : Optic axis is the line passing through the center of the cornea as well as center of all the elements of the eyeball . VISUAL AXIS : visual axis is the line joining the Fixation point , Nodal Point ,and the fovea. FIXATION AXIS : It is the line joining the Fixation point and center of rotation.

9. ANGLES ANGLE ALPHA : Angle formed between the optic axis and visual axis is called angle alpha. ANGLE GAMMA : Angle formed between optic axis and fixation axis is called angle gamma. ANGLE KAPPA : Angle formed between the visual axis and pupillary line is called Angle Kappa .

10. REFRENCES Text book of optics and refraction. Google.

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