Refracting Telescope, Newtonian Telescope and Schmidt Cassegrain Telescope: The Differences

Let us enumerate the differences between the Refracting telescope, Newtonian telescope and Schmidt Cassegrain Telescope. Hopefully this will help astronomical and stargazing newbies to decide what kind of amateur telescope they would like to have.

Refracting Telescope

Galileo’s version of his telescope is a refracting telescope – and it was during its invention that astronomical pursuits are put to a higher level.

The refracting telescope's lens is convex, meaning it is thicker in the middle than its edges. It is for this reason that the light which passes through the edges are more bent than in the middle, with the lens gathering all the light to go to a focal point – the point where the image is formed.

One disadvantage of refracting telescopes is what we called chromatic aberration – which basically means the all light that go through don’t focus on a single point, making the image blurred. A specialized lens can be used to counteract the effect of chromatic aberration and make the images more vivid.

Newtonian Telescope

Named after its inventor Sir Isaac Newton. If you are a newbie in need of an amateur telescope – this is the best telescope for you. As a beginner telescope, the Newtonian is quite cheap but still very effective. It has a parabolic mirror that focuses an image to a diagonal. This diagonal sends the image to an eyepiece on top of the telescope tube.

One disadvantage of Newtonian telescope is what we call Coma, an aberration in which the image is set off the optical axis. You are experiencing this defect if the stars you are observing are having tails like that of comets, either flaring away from the axis or pointing toward it.

The Newtonian is the simplest of all reflecting telescopes.

Schmidt Cassegrain Telescope

An invention by German scientist and astronomer Bernhard Schmidt and French Cassegrain.

Schmidt Cassegrain is a combination of the refracting telescope and reflecting telescope, extracting the best qualities of the two. Schmidt Cassegrain is currently a favorite instrument for astronomic photography.

This telescope has a corrector that is intended to minimize if not eliminate spherical aberration. It also has primary and secondary mirrors – with the primary mirror having a hole through which the light reflected by the secondary mirror passes.

Aside from an excellent telescope for astrophotography, the Schmidt Cassegrain telescope is one of the most popular among amateur astronomers.