Optics
The Orion GoScope 80mm is an achromatic refractor telescope. Despite the limitations imposed by the relatively small size of its aperture, the GoScope has surprisingly good optics that result in good image clarity and brightness.
Refractor telescopes are those that use lenses to gather and focus light before it reaches the eye of the viewer. As we've talked about elsewhere, refractor telescopes have one of the simplest and long-serving designs. The design for the original refractor dates back to the 17th century.
Image: Diagram of a refractor telescope
The benefits of refracting telescopes include lower cost. Lenses of the sort used in simple refractors can be cheaply manufactured, thus allowing entry-level buyers to get a better telescope than they might be able to were they to buy a reflecting telescope. Another benefit of refracting telescopes is that their optics tend to be fixed within the tube of the telescope, thus reducing the amount of collimating that must be done. This is particularly attractive to beginners, as it means you can just set the scope up and look, rather than having to manage the learning curve (and time) inherent in correctly aligning the mirrors in a reflecting scope. The lack of maintenance in the GoScope can be a boon to someone looking to integrate astronomy into their schedule for the first time.
There are, however, a few issues with refracting telescopes that one must consider in buying. First, while only the surface of a mirror must be flawless for a reflecting telescope's optics to transmit a true image, the entire lens must be free of defects in a refracting telescope. This is because, while light only contacts the surface of a mirror, it must pass through a lens. The result of this is that imperfections within the lenses of a refracting telescope can result in greater distortion than they would beneath the surface of the mirror of a reflecting telescope.
The second issue with the use of lenses is chromatic aberration. Chromatic aberration is an effect that results from the refracting of different wavelengths of light at different rates. Thus, the different colors of light that pass through can end up in different places. A perfect example of this is a prism refracting sunlight. While this phenomenon results in pretty patterns of light on the walls of your house, it can be a serious detriment to image clarity in a telescope.
In order to solve the problem of chromatic aberration, telescope makers must include some sort of correction to reproduce a true image. One way to achieve this is to create a lens containing different materials that refract the different wavelengths in such a way as to produce a true image. This sort of lens is known as an "achromat", a technique that Orion uses in the GoScope 80mm to good effect.
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Given that we're in that 60mm - 80mm diameter aperture range appropriate for beginners, you can guess where the GoScope is most effective. It's best used for viewing terrestrial objects and brighter celestial phenomena, such as Orion, Andromeda, the Messier objects, along with the Moon and planets.
But it's no slouch. The GoScope has a clear light path to allow all the light entering the objective lens to reach the eyepiece, especially in the center of the field of view. The result is that it offers nice, crisp images in the center of the field of view. Images with enough light are visible with almost as much clarity as you can expect to find on more expensive telescopes. In some ways, the GoScope even outperforms higher-cost scopes in this regard.
Because of the GoScopes short focal ratio, some objects can become distorted nearer to the edge of the field of view, but this in no way diminishes the fact that this is a highly effective scope at a reasonable price.
The GoScope 80mm comes with two eyepieces, one 10 mm with 17.5x magnification, and the other 20 mm with 35x magnification. These fairly low levels of magnification are actually well calibrated to the best used and specifications of the scope, as an excessive amount of magnification with this size aperture would just make locating objects more difficult.
The eyepieces attach with Orion's own proprietary threading system. This could present an issue for those looking to attach some accessories, such as an erect-image eyepiece, but it's not a major issue.
One of the things you immediately notice about the GoScope is its quirky focusing mechanism. Whereas most telescopes have a static objective lens and move the eyepiece to focus, the GoScope does it the other way around. The eyepiece is static and the front lens is the one that moves when you focus. We were skeptical at first, but this works nicely, and focus is smooth and fast without lacking control.
In fact, this is a theme that comes to mind a lot with the GoScope: it has a very user-friendly design that just works.
The GoScope is mounted on a tabletop swivel alt-azimuth mount. It swivels up and down and left and right. Of course, under normal circumstances this will require a tabletop to stabilize the telescope.
The motion of the mount is smooth and simple. Not a lot of frills here, but it is stable and gets the job done.
Not everybody is in love the with idea of using a table-mounted telescope. If you're one of these people, the mount also comes with a threaded adapter for use on a standard tripod.
Accessories
Orion equips the GoScope with their standard EZ Finder II, which projects a red dot onto a window in the finder. As you view the target through the window, you move the scope until the red dot lines up with the target.
This works fairly well, and it's certainly better than a lot of the finder scopes on the market. We found the red dot to be a bit too bright; it might be more effective if it were a bit dimmer.
