1) Arrange a retort stand.
2) Collect wooden sticks (or) PVC pipe that are used for electric wiring.
3) Prepare sticks or pipes of 20 cm, 30 cm, 35 cm, 40 cm, 50 cm from them.
4) Keep the retort stand on a table and stand near the table such that your head is beside the vertical stand.
5) Adjust the clamp on horizontal rod and fix at a distance of 25 cm from the eyes.
6) Ask one of your friend, fix wooden stick of 30 cm height to the clamp in vertical position.
7) Now keeping your vision parallel to horizontal rod of the stand, try to see the top and bottom of wooden stick kept in vertical position.
8) If you are not able to see both end of stick at this distance (25 cm), adjust the vertical stick on the horizontal rod till you are able to see both ends of the stick at nearest possible from your eye.
9) Fix the clamp of containing vertical stick at this position.
10) Without changing the position of the clamp on horizontal rod, now replace this stick of 30 cm length.
11) Try to the top and bottom of the stick without any change in the position of eye.
12) Try the same activity with various lengths of the sticks.
13) You can see the whole object AB which is at a distance of 25 cm (least distance of clear vision) because the rays coming from the ends A and B of the object will enter into the eye.
14) Similarly we can also see complete object CD with eye as explained above.
15) Let us assume that AB is moving closer to eye to a position A'B'.
16) You notice that you will be able to see only the part (EF) of the object AB' because the rays coming from E and F enter into your eye.
17) The rays coming from A' and B' cannot enter into your eye.
18) The rays coming from the extreme ends of an object forms an angle at the eye.
19) If this angle is below 60°, we can see whole object.
20) If this angle is above 60°, then we see only the part of the object.
21) This maximum angle, at which we are able to see the whole object is called angle of vision.
22) The angle of vision for a healthy human being is about 60°.
23) It varies Person to person and with age.