Visual Comparisons Between Two Telescopes
Dan Boyar - April 2, 1999
I recently purchased a Maksutov-Newtonian telescope (MN56) from Mike Palermiti and had several opportunities to compare it with my 6-inch F/8 Edmund Newtonian reflector. The MN56 is a 5-inch F/6 system (30-inch focal length) with a central obstruction of 23.4 percent. The coatings are excellent and Mike’s evaluation of this instrument can be found on ITE’s Web page at Astromart.com. The Edmund is a classic instrument from the early 1960s, with an excellent parabolic primary [mirror] of 48-inch focal length. The central obstruction is only 16 percent and is supported by a thin single stalk. Coatings are fairly good but by no means excellent. Seeing conditions were good-to-excellent when the comparisons were made.
The planets showed more detail in the 6-inch telescope. Saturn was brighter and whiter compared to the 5-inch, and showed finer object detail at higher powers. (Remember, however, that we are comparing a 5-inch to a 6-inch telescope. A 5-inch resolves to 0.88 arcseconds, while a 6-inch can resolve to 0.73 arcseconds). Jupiter was also brighter and lighter in the 6-inch, and showed finer object detail than the 5-inch. The planetary performance of the 5-inch was still very good despite its 23.4 percent obstruction, and the planets showed better color saturation than with the 6-inch scope. Saturn was golden in the 5-inch and also showed many fine details, including a sharply defined Cassini’s division, the Crepe ring and the rather elusive equatorial belt. Jupiter showed similar rich color saturation, with brownish cloud belts and a pinkish Great Red Spot within the larger Red Spot Hollow.
Similar results were obtained when observing the moon. The 6-inch scope showed noticeably finer detail. The 5-inch was no slouch though -- 4 tiny cratelets on the floor of Plato were readily resolved. The 5-inch scope also did things that the 6-inch could not. The color response in the 5-inch rendered splendid, contrasty views of the lunar maria, rays and sunlit slopes. In general, the 5-inch showed greater variety in the hues and greater contrast. Some areas gave off a golden luster, while others had a silvery luster. The maria looked like they had floors of soft powdery dust. These aspects were not apparent in the 6-inch telescope.
On the deep sky, the instruments produced much more similar images from my light polluted back yard. The 5-inch did just about as well as the 6-inch. Both instruments easily and very clearly showed the 6 stars of the Trapezium at 100 power. The nebulosity was a bit stronger in the 6-inch, but not much. The Crab Nebula was a faint mist in both scopes. For wide field views and freedom from comatic distortion, the 5-inch was the clear winner. The Pleiades could be easily fielded in the 5-inch at 32 power and 40 power. In the 6-inch at 51 power, I could just barely fit the brightest members of the group into the field of view. Double star performance in both instruments was excellent. At high magnifications, both instruments showed clean stellar diffraction patterns. While the 6-inch showed smaller, tighter diffraction patterns, the color response was, again, not quite as good as it was in the 5-inch scope.
Finally, something should be said about ergonomics. The MN56 is only about 2/3 the size of the 6-inch Edmund telescope, but weighs about the same. The MN56 is also the more rugged instrument and will hold collimation better. Also, with its closed-tube design, it is less affected by tube currents. Sitting low on the Edmund equatorial mount, the MN56 could be used in many observing positions, including overhead, while seated in a chair. This was not possible with the 6-inch Edmund. In summary, the MN56 is a versatile telescope with excellent performance characteristics. The 6-inch Edmund Newtonian, while not as versatile, had the advantage for high-resolution work on the moon and planets.