What is astigmatism?
In astigmatism, a person can sea only in one plane either horizontal or vertical. When light rays enter the eye they do not focus correctly on the retina, resulting in a blurred image. Astigmatism is caused by irregular shape of cornea ( not perfectly spherical) and is corrected using cylindrical lenses.
Why the Sun appears reddish at the sunrise or sunset.
At the sunrise /sunset, light from the Sun has to cover larger distance in the earth’s atmosphere before reaching our eyes. Since red colour light has longer wave length it deviates the least than other colours light and reaches our eyes.
What is Persistence of vision?
The impression of image is remains on retina for about 1/16th of second. This is used in cinematography. The sequence of still picture taken by movie camera is projected on the screen at he rate of 24 or more images per second so that images merge in one another on screen and we are able to see a movie.
No comments:
Post a Comment