Various lenses

There are two kinds of lenses, namely:
a. Convex lens is a lens that is thicker than the middle part of the edges. Real fire point. Concentrated beam of light that is refracted. The distance from the lens to the so-called hotspots within hotspots. The thicker the lens, the shorter the distance the fire point. The nature of shadows: shadows can form real or virtual, upright or inverted, bigger or smaller than the objects (depending on the location of the object to the lens). The main beam on the convex lens.
b. Concave lens is a lens that is thinner than the middle part of the edges. The nature of the shadow: always virtual, upright, smaller than the object.