Notes on Optical Instrument for IIT Mains
Ray Optics/Notes on Optical Instrument for IIT Mains
Download Notes on Optical Instrument for IIT Mains
STRUCTURE OF EYE
Notes on Optical Instrument for IIT Mains – Fig. Shows the eye, light enters the eye through a curved front surface, the corner. It passes through the pupil which is the central hole in the iris. The size of the pupil can change under control of muscles. The light is further focussed by the eye-lens on the retina. The retina is a film of nerve fibres covering the curved back surface of the eye. The retina contains rods and cones which sense light intensity and colour, respectively, and transmit electrical signals via the optic nerve to the brain which finally processes this information. The shape (curvature) and therefore the focal length of the lens can be modified somewhat by the ciliary muscles. For example, when the muscle is released, the focal length is about 2.5 cm and (for a normal eye) objects at infinity are in sharp focus on the retinas. When the object is brought closer to the eye, in order to maintain the same image-lens distance ( @2.5 cm), the focal length of the eye-lens becomes shorter by the action of the ciliary muscles. This property of the eye in called accommodation. If the object is too close to the eye, the lens cannot curve enough to focus the image on to the retina, and the image is blurred.
Notes on Optical Instrument for IIT Mains – The closest distance for which the lens can focus light on the retina is called the least distance of distinct vision, or the near point. The standard value (for normal vision) taken here is 25 cm. (Often the near point is given the symbol D.)
You may also like
- Click on >> (Arrow) to Download