In physics, we call an optical instrument any instrument whose purpose is to capture, enlarge and reduce the image of objects. The camera that we handle daily is an optical instrument, the magnifying glass also fits perfectly into the description of an optical instrument and, finally, we could not fail to mention the glasses and binoculars. Well, all these instruments and a few more – which we have not mentioned – are considered optical instruments.
Another optical instrument that is widely used is the so-called image projector. These projectors can be slide projector , overhead projector, episcope, etc. All these instruments are considered objective vision instruments. Therefore, it is thanks to these devices that the real image of an object can be enlarged and projected onto a screen.
The image projector is basically made up of spherical lenses of the objective converging type, a very intense light source and a concave mirror whose center of curvature coincides with the position occupied by the light source, in order to make better use of the light emitted by the source.
Let’s see the figure below, in it we have the simplified form of the image of an object clearly projected. Let’s see:
Note that the object must necessarily be between the anti-main object point and the main object focus of the lens. In this way, when we bring the lens closer to the fixed object, the image tends to move away from the lens and increase in size.