Scopes are optical instruments that revolutionized astronomy. They are approximation instruments consisting of two lenses arranged coaxially.
The astronomical telescope is an approximation instrument that uses two lenses arranged coaxially: the objective and the eyepiece. The objective has a focal length of the order of meters, while the focal length of the eyepiece is of the order of centimeters.
From a real, distant object, the objective produces a real image i1 located at the image focus of the objective. This image behaves as an object for the eyepiece, which works as a magnifying glass, producing a final i2 image that is virtual and inverted in relation to the object. (fig. 3)
Around 1680, Isaac Newton developed the reflecting telescope in order to solve the problems of chromatic aberrations in the refractors of his day. In place of a lens to capture light, Newton used a curved metal mirror (primary mirror) to capture this light and reflect it back into focus.
A concave mirror produces an image of a distant object at its focus. This image behaves as a virtual object with respect to a plane mirror, which in turn provides a real image to the eyepiece lens, which functions as a magnifying glass. (fig. 4)
One of the most famous telescopes in the world is the Hubble telescope, which has an objective of 2.40 meters in diameter, and is in orbit at a distance of 600 km from the Earth’s surface.
Scheme for determining the image in the telescope.