ETX-125EC Reviewed by Sky & Telescope

S&T Test Report: Meade's ETX 125EC -- A First Look By Gary Seronik Adapted from Sky & Telescope October 1999	This 5-inch Maksutov telescope starts where the original 3.5-inch left off.
Above: Featuring twice the light-gathering capability of its 90-millimeter predecessor, the ETX-125EC Maksutov takes the concept of economical and portable Go To telescopes to a new level. Eclipse chasers and fans of astronomy travel will value the 125EC's compact dimensions. With the right travel case, this scope could qualify as carry-on luggage (sans tripod) on most commercial airlines.
Update to This Review As mentioned in our first-look review of the Meade ETX-125EC telescope, Meade engineers identified a source of image vibration in the original design of the telescope we tested. We have now examined a new telescope supplied by Meade and also one that we purchased anonymously. Image vibration induced by the ETX-125's drive motors has been reduced to negligible levels. With the telescope operating in altazimuth mode and the azimuth and altitude motors running at tracking speed, no image vibration is apparent. The well-known multiple star Epsilon Lyrae, the Double-Double, was easily split into its four components at magnifications of 142x, 212x, and 340x.
Amid the clamor and excitement surrounding the release of Meade's ETX-90EC earlier this year one could hear voices saying, "That's nice -- but it is only a 90-millimeter scope!" For those seeking more light grasp, Meade has responded with a 5-inch version of its groundbreaking low-cost Maksutov-Cassegrain. But could this big brother ETX match the superb optics and Go To accuracy of its smaller sibling? To find out, S&T obtained two early production units directly from Meade. Here's what we found.
Go To Take Two Like the 90-mm ETX, the 125EC comes with motorized tracking and slewing capability and a basic hand controller as standard equipment. For the optional Go To capability, both ETXs utilize the same Autostar controller (see the May issue, page 61, for a description of features). However, because the 5-inch ETX has a longer focal length and thus a smaller field of view, identical electronics do not guarantee identical performance. For Autostar to place objects in the eyepiece of the 5-inch scope, the system's pointing accuracy would have to be nearly twice as good as with the original ETX.
Right: Weighing in at nearly 19 pounds, the 125EC demands care when being attached to its field tripod. Once secured with two hand bolts, the resulting assembly is quite top-heavy. Particular care must be taken when the scope is configured for use in the polar mode because much of the telescope's mass is offset from the center of the tripod.
To evaluate the 125EC's Go To accuracy, I selected 10 stars distributed evenly over the sky and had the scope find them one at a time. To make this a worst-case test, I made the scope swing across at least half the sky to go from one star to the next. For example, after I sighted Antares, the next star on my list was Gamma Cassiopeiae, and then Spica, forcing the scope to make long slews. So how did the new ETX do? Using the supplied 26-mm Plössl eyepiece, Autostar put the target star into the 45-arcminute field of view 87 percent of the time. Usually the star was closer to the edge than to the center. (This is reasonable since only 1/4 of the field of view's area lies inside the center half of the field's radius.) This percentage held up regardless of whether the scope was used in polar or altazimuth tracking modes. And when Autostar missed, it wasn't by much. In fact, using a 35-mm Plössl that produced a 1° field (the maximum possible with the 125EC), the test star was always in the field of view. We mounted our test units on the model #883 Deluxe Field Tripod -- the same tripod recommended for the lightweight ETX-90. To improve stability, the 125EC comes with a 1/8-inch-thick metal plate designed to fit between the tripod head and telescope base. The vibration-damping time for this setup depended to some extent on the orientation of the tube and ranged from 3.5 to 4.5 seconds for both altazimuth and polar modes. This proved to be most troublesome when focusing. A set of Celestron Anti-Vibration pads placed under the tripod legs cut the damping time by more than half.
Optics The optics of the 90-mm ETX have drawn considerable praise for their quality and consistency. Will the 5-inch model match this high standard? If the two samples we received from Meade can be taken as reliable indicators, the answer is yes. Careful testing showed that both 125ECs featured excellent optics. Stars at the center of the field focused to sharp points, free of astigmatism or other aberrations. Bright stars were surrounded by a faint halo of scattered light and off-axis star images displayed some coma, suggesting that this Maksutov has a slightly different optical recipe than the 90-mm ETX. Neither problem detracted from the viewing experience.
	Left: Meade offers an optional electric focuser ($119.95) designed specifically for the 125EC. This user-installed option effectively eliminates the jiggles introduced by manually focusing the telescope.
Maksutov telescopes have acquired a reputation for first-rate planetary views. As a solar-system observer myself, I was curious to see how the 125EC would perform with Mars (which was nearly two months past close approach during the test period) and the Moon. Mars appeared crisply defined though its surface markings proved elusive. Views of the Moon were pleasingly sharp and rich with satisfying detail.
	Left: Although necessary to prevent stray light from reaching the focal plane, the flared secondary baffle shown here increases the size of the ETX-125EC's central obstruction to nearly 40 percent. Instruments optimized for high-resolution planetary views should have central obstructions less than 25 percent of the scope's aperture.
On several nights I set up the ETX next to my home-built 4.2-inch f/6 Newtonian, my favorite "quick-look" instrument. Using the same magnification, I found an obvious difference in performance -- the Newtonian showed the Martian surface markings with greater certainty than did the 5-inch Maksutov. The red planet seemed drained of low-contrast detail in the 5-inch view. This is most likely a consequence of the 125EC's large central obstruction -- nearly 40 percent the diameter of the aperture. An obstruction this size has the effect of reducing the 5-inch scope's contrast to that of an optically excellent unobstructed 3-inch instrument (see "Rules of Thumb for Planetary Scopes -- I," Sky & Telescope, July 1993, page 91).
Right: Testing showed that the mount's damping time is cut in half by using a set of Celestron vibration-suppression pads. This accessory should be a high-priority item for anyone considering the ETX-125EC and optional field tripod combination.
Motor vibrations also affect the image. One evening I decided to have a look at the well-known Double Double, Epsilon Lyrae, high overhead. This pair of pairs features doubles separated by 2.3 and 2.6 arcseconds -- easy splits for a 5-inch instrument. To my surprise, the ETX showed only the two main stars (Epsilon1 and Epsilon2) despite the steady seeing conditions of a muggy summer night. Puzzled, I switched off the drive, and magically all four stars popped into view. Further investigation revealed that vibration introduced by the altitude motor was the culprit. Indeed, at 100x one could watch stars bloat up and shrink down as the motor drove the scope in altazimuth-tracking mode. As this review was being readied for press, Meade engineers contacted us to say that they had identified this problem and implemented a fix. Here are the details. Use your BACK button to return to this review. Although the focusing mechanisms worked smoothly on both scopes, one exhibited approximately 2 arcminutes of focus shift, while the other had a fraction-of-a-turn dead spot when the focus direction was reversed. This made precise focusing at high magnification more difficult than I would have liked. The 125EC comes with an 8x25 right-angle finder with a focusing eyepiece -- a vast improvement in usability over the ETX-90's straight-through finder. While stars at the center of the field were sharp, those slightly off-axis stretched out into astigmatic streaks.
	Left: Although the ETX-125EC with Autostar can track the stars and planets, it is not an instrument suited to long-exposure astrophotography. The scope is, however, capable of producing satisfying snapshots of the Moon. The author obtained this view with a manual 35-mm camera equipped with a 2x teleconverter yielding an effective focal length of 3,800 mm.
Telescopes are compromises we look through -- no one instrument can satisfy the interests of all observers. The ETX-125EC is not a specialist's scope -- it is a general-purpose instrument with twice the light grasp of the 90-mm version. If what you're after is 5 inches of portable aperture with Go To capability and good optics, and you're willing to overlook the telescope's shortcomings, this just might be the compromise for you.

Courtesy of Sky & Telescope

Note on the Meade ETX-125EC

In our review of Meade's new 5-inch Maksutov-Cassegrain telescope (S&T: October 1999,
page 61 and "Meade's ETX 125EC -- A First Look" , we note several mechanical problems.
The manufacturer has identified the cause of some of them and says that units shipped
after August 15th should be free of these problems.
If you have a Meade ETX-125EC delivered before this date, Meade is offering to fix it at no cost to you.
For details, see Meade's Web site. Note: Once S&T's editors have had a chance
to evaluate a modified ETX-125EC, we'll post an update too.