Question

Two greenish birds 15 cm apart at distance 350 meters from an observer. What would be a
suitable lens for his binoculars for a perfect view? Explain and discuss your result.

Answer 1

Binoculars make use of two convex lens. The front lens that faces the point of observation and converges light rays that are coming from the birds and makes a focused image of it at a short distance which is behind the lens.The second lens is again a convex lens that picks up the image of the bird that is formed by the first lens and magnifies it.

The Binoculars have some sought of code written on it which has the form in general "mxd"where m stands for magnification power and d is the diameter in millimetre of the Objective lens.
Since the birds are situated at a distance of 350m we could use a binocular with magnification 10x for a clear veiw. Here,the magnification will be 10 times,but as you would expect field of view will narrow down.It is however suitable for this purpose.Bird watchers usually also prefer to use 8x42 which means magnification is 8 times and the objective lens has a diameter of 42 mm this gives a smaller image that’s wider and brighter but not suitable for watching over a long distance.