1. Your optical tube assembly is nothing more than the main body of your telescope. Often shortened to OTA, to further confound the novice, this part of your telescope can be modified, built from scratch, or repaired, depending on your level of expertise.
2. Those interested in optical tube assemblies are generally among the more experienced amateur astronomers who are looking to dive deeper into how, exactly, we get these stunning images of outer space.
3. As with any optical products, particularly those used in astronomy, you can spend anywhere from about 100 dollars to tens of thousands of dollars on optical tube assemblies. The cheaper ones are great for hobbyists, while there are some online that are strictly for institutional and professional use.
4. You'll see optical tube assemblies offered by just about every optics firm out there, but Vixen, Orion and Celestron seem to offer the most online with the widest range of privately accessible prices. After finding your optical tube, you can outfit it with any number of optical tube accessories such as eyepiece holders, weights, focusing aids, and finderscopes.
5. The great thing about optical tube assemblies is that you aren't short-changing yourself on quality at all. Many DIY projects, or anything that requires some tinkering, results in a product that doesn't compete with what comes from the factory; this isn't necessarily the case with optical tube assemblies. Options are available for all levels of amateur astronomy, including use with software for finding, tracking and photographing celestial bodies.