Maksutov-Newtonian Telescopes

Maksutov-Newtonian telescopes, or Mak-Newts, are a form of catadioptric telescope that uses both mirrors and lenses to bring light into focus. The Mak-Newt combines a concave meniscus lens with a spherical primary mirror. The purpose of the meniscus lens is to eliminate the spherical aberration that would otherwise result from the use of a spherical primary mirror. The meniscus lens also greatly reduces coma, which is present in all Newtonian telescopes. Coma is an off-axis aberration that causes stars at the edge of field to appear more like small comets with a fanned tail. The effect of coma becomes more severe with faster Newtonian systems (i.e. systems with lower focal ratios.)

Another benefit of the Mak-Newt design is that the flat secondary mirror can be attached to the back of the meniscus lens, eliminating the diffraction spikes caused by the spider vanes used in Newtonian systems. The net result of the Maksutov-Netonian design is a telescope that performs much like a high quality refractor at a lower cost per unit aperture. Mak-Newts are capable of producing very low-power widefield views, yet they are also capable of providing very high magnification as needed for planetary observations. Maksutov-Newtonians are an excellent choice for either visual observing or astrophotgraphy.

Why don't you see more Mak-Newts in the field?

OK - if you read the paragraphs above then you must be asking what the catch is. Maksutov-Newtonians perform like expensive refractors, yet refractors are far more common, but why? Like any Newtonian system, the Mak-Newt produces an inverted image, making it essentially unsuitable for terrestrial observing. Refractors produce an upright image, making them useful for both terrestrial and astronomical observing.

Are there any disadvantages in contrast to the standard Newtonian design? Like any closed tube design, the Mak-Newt will require more time to reach thermal equilibrium than an open tube telescope. Heat rising from the primary mirror will stimulate tube currents, or convection airflow within the optical tube. This produces an unsteady image, similar to the mirage effect. Mak-Newts and other closed tube reflective systems are not the best choice for "quick looks" telescopes. A best practice with these telescopes is to set them up just after sunset, as they should reach thermal equilibrium before it is dark enough for serious observations.

The bottom line on the Maksutov-Newtonian telescope is that, in our opinion, the advantages outweigh the disadvantages by a wide margin. If you crave high contrast and pinpoint stars over a wide range of magnifications but cannot afford a six-inch apochromatic refractor, give these telescopes a serious look.