Question

Can a telescope be constructed using two concave lenses? If not, why? And if it is possible, how does it work?

Answer 1

Two lenses are needed to build a telescope. We call these the "objective" lens and the "eyepiece" lens. The "Objective" lens should always be a convex lens. Convex lenses are thicker in the middle and can be used as magnifying glasses or for concentrating sunlight. The "eyepiece" lens can be either a convex or concave lens. If you use a convex eyepiece, your telescope will turn everything upside-down. This kind of telescope is called a "Newtonian." And if you use a concave lens as your eyepiece, your telescope will not turn things upside-down. This type of scope is called a "Galilean."
If the lens is concave (thinner in the centre,) everything you see in the lens will get smaller and smaller as you move the lens farther away from your eye. If you use a convex lens instead, everything will get bigger and bigger as you move it away. The convex lens is the interesting one because it makes things bigger when you move it farther from your eye. By moving the convex lens in and out, we can change the size of everything, or make it all go upside-down or right-side-up.