Review / Video: Orion Short Tube 120, a Classic Entry-Level Refractor

The author’s Short Tube 120 ready for observing on an equatorial mount, with a finder, and diagonal. Credit: Ed Ting

The telescope bargains just keep on coming. Take, for example, the Orion Short Tube 120, a 120 mm f/5 achromatic refractor.

Due to their high costs, it was rare, until recently, to see a refractor this large at any price, let alone one selling for only $249 (note: optical tube only). However, recent offshore manufacturing has brought refractor prices down to earth. You will still need to outfit the optical tube with rings, a mounting plate, finder, diagonal, eyepiece, and mount. While experienced astronomers will already own many of these accessories, beginners will need to budget accordingly.

Refractors are renowned for their ability to deliver sharp, high-contrast images. Among the major telescope designs, they are the only ones to feature an unobstructed optical path to the eyepiece. As a result, refractor owners can be a passionate bunch, often declaring they will not look through anything else.

The Short Tube 120 has a 120 mm (4.7-inch) f/5 objective lens that gathers light. 4.7 inches is not considered large by reflector or Schmidt-Cassegrain standards, but due to the higher transmission efficiency of lenses (as opposed to mirrors) and the lack of any central obstruction, the 4.7 inch can seem to deliver views similar to a larger telescope. In addition, the higher contrast of a refractor can bring out “troublesome” low-contrast objects like galaxy M33 in Triangulum, or galaxy M101 in Ursa Major.

Is the Orion Short Tube 120 perfect? Of course not. All but the most expensive refractors suffer from chromatic aberration, or false color. Remember when you were a kid in school, and the teacher handed you a prism to play with? It threw a pretty rainbow up on the wall. This rainbow is nice to look at, but this is the last thing you want in a piece of precision optics.

The problem is, all glass will do this to some extent. Optical engineers have gotten good at reducing, but not eliminating, this false color in telescopes, microscopes, binoculars, etc. over the years. But the color still remains, if you know where to look. It is most visible as a mild purple halo of light around bright objects like stars. Here is a blown up, slightly enhanced view of the star Vega, taken through this telescope.

The bright blue star Vega through the Short Tube 120. Credit: Ed Ting

Even with the false color, this telescope can yield some impressive astrophotos. See these images, taken by the author through this telescope.

The Dumbbell Nebula. Credit: Ed Ting
The North American Nebula. Credit: Ed Ting

The last paragraph illustrates an important point. No telescope is perfect. No matter what you select, you will be gaining something, and losing something. Color-free refractors (called apochromats) for example, do exist; in this case, what you will be losing is money, and potentially lots of it!

It is perhaps best to appreciate a telescope like the Orion Short Tube 120 for what it is – an inexpensive entry into the formerly rarified world of the refractor. Even if you don’t care about this, the Short Tube 120 is a competent, attractively priced telescope that can teach you a lot about the night sky.

Happy viewing!

PS: For more on the Orion Short Tube 120, check out my YouTube video on this telescope, which covers more advanced topics.

About Ed Ting

Ed Ting is a well-known amateur astronomer. His work has appeared in Sky & Telescope, Night Sky, Skywatch, Amateur Astronomy, Discover, and Popular Mechanics magazines. His web site, www.scopereviews.com, is a widely-read telescope review web site. He is a National Science Foundation Ambassador to Chile and a NASA Solar System Ambassador.

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