In my opinion, the best telescope design for smaller apertures is the refractor. In the 3- to 5-inch range, these are typically small and light, easy to store and transport. They are simple to mount, make great wide-field instruments, and are relatively rugged. Their practically nonexistent cool-down times combine with their wide fields of view to make them fantastic grab-and-go telescopes. Perfectly suited for a peek at the summer Milky Way or some in-depth lunar and planetary investigations, a refractor can do it all.
For many years, the standard in refracting technology was the achromatic doublet. Such a telescope has a two-element front lens that features high-quality color correction.
That said, bright objects like the Moon and Jupiter tend to show varying amounts of false color through such doublets. The types of glass used in the lens — typically flint and crown — don’t bring all colors of light to the same focus. Manufacturers partially compensate for this problem by building in a long focal ratio. This means a long optical tube, which trades portability for optical quality.
The apochromat (meaning without color) is a decided improvement over the achromat, especially when it comes to fast-focal-ratio scopes. Apochromatic (APO) telescopes use special types of glass to bring the wavelengths of visible light closer to common focus, thus eliminating (or at least greatly reducing) the purple fringe seen in achromats.
The one drawback of the modern apochromatic refractor is cost. These special types of glass don’t come cheap. Luckily, recent changes in the world economy have made them more affordable than ever. Into this market comes the affordably priced Levenhuk Ra R110 ED Doublet OTA.
