Choosing the right telescope

So I decided to start amateur astronomy, an idea hanging around for some time now, and as anyone else who did, I asked myself: which telescope ? First, let’s review the main types of telescopes on the amateur market.

The most familiar type is the refractor, with a lens at the front, but they get expensive faster than the other types as aperture increases. Then, many telescopes are Newtonian reflectors, with a primary mirror at the back of the tube and a secondary mirror near the opening which reflects light at a 90° angle. They are the cheapest for larger apertures but require regular collimation to fix the light path inside the tube. They’re also open, which means they need cleaning, but they can cool down quickly. With a good quality parabolic mirror, the only visual drawbacks are diffraction spikes caused by whatever holds the secondary mirror. Another common class of instrument, called catadioptric, combines a lens at the front (a corrector plate) to eliminate or reduce optical aberrations, and a mirror at the back. They’re usually built in a Cassegrain configuration, with a secondary mirror near the opening as in a Newtonian, but reflecting light right at the back of the tube, through a hole in the primary mirror, making the tube much shorter than its effective focal length. They’re also sealed (less cleaning, more cooldown time) and robust, making collimation rare. The two most popular types of these are the Schmidt-Cassegrain (SCT) and the Maksutov-Cassegrain.

The most important property of a telescope is its aperture. Basically, the bigger, the better. But it had to be small enough that it could be carried along when traveling. Because of that, I decided to get a Cassegrain telescope and, for the same aperture (up to about 180mm), Maksutov-Cassegrain telescopes are cheaper than SCTs, with similar quality. I restricted my celestial targets to the solar system and the brightest deep sky objects only, so that an intermediate aperture would do the job. I worried a little about DSOs because of the high focal length of such telescopes, but this can be solved with a focal reducer.

As a result, I bought a Sky-Watcher SkyMax 127/1500.

After a few sessions, I must say I’m quite happy with the results. Although it takes time for the telescope to cool down (roughly 30-60 minutes), the sharp images it produces are worth the wait. The only drawback I’ve seen so far is the very sensitive focusing mechanism, but there are accessories to improve the situation.