Courtesy of
Astronomy
February 1999

Make the Most of Your Meade ETX

A galaxy of add-ons make using this small scope an absolute joy.

by Steve Edberg

     Whether the product is an automobile or a telescope, accessories for it are often produced by other firms. In the case of a good product, the list of accessories is long, and so it is with Meade's ETX telescope.
     The Meade ETX is a 90mm f/13.8 Maksutov-Cassegrainian telescope mounted on a battery-powered clock-driven fork mount. It makes a small, easily transported package for use in the backyard or out in the field. Four manufacturers responded to a solicitation to review their products.

Tripods

     The ETX comes with legs to use for tabletop polar alignment but most serious users will want a sturdy tripod. JMI has modified the Velbon S-6000 photographic tripod for the ETX. It includes flip locks on the legs for quick setup and take-down and has reinforcement bars that connect to a sleeve that slides on the centerpost.
     Three options are offered by JMI. You can purchase the wedge/tripod ($119 + $119), the "wedgepod" (a prototype was delivered, $189), or the wedge only ($119) and supply your own tripod. The wedge/tripod combination is a sensible choice if you use the ETX in altitude-azimuth for terrestrial observing as well as for astronomical use. The mounting platform on the tripod is large and flat. The wedgepod permanently mounts the wedge on the tripod, although the wedge must be folded down in order to level the instrument in the altaz mode. To polar align, everything must be moved to adjust azimuth. Tap tests on the tripod legs and wedge assemblies showed damping in two seconds or less.
     The wedge, with its spirit level, can be mounted on other tripods using either 1/4-inch or 3/8-inch (preferred) mounting holes. It also has adjustable rubber feet for use on a tabletop. The wedge has an indicator for latitudes from 20 to 57 , and can be used from about 19 to 58 (8 south of the Arctic Circle, contrary to the ad statement). The prototype wedgepod is limited to about 20 to 50 latitude but JMI says they will expand this in the future.
     When the ETX is equatorially mounted on a tripod or wedgepod, the center of gravity is not directly over the centerpost. One can see the opposing tripod leg vibrate. This offset was also present on my Bogen 3040 tripod (with head) as well, and the leveling of the wedge disappeared when the ETX was added to my Bogen+wedge.
     The Tuthill Isostatic Equatorial Mount ($270 if purchased separately) is intended purely for astronomical use. I was initially skeptical about this unit because of the long legs but found some real advantages as I used it.
     This tripod is short enough (45 inches) that grade school children can reach the eyepiece of the ETX, and adults won't have to bend down too far. It's great for use at star parties. The wide spread of the long legs also permits viewers to move easily in and out if they are queued up for a look-through. That wide spread is useful in another way: A chair conveniently fits between the legs and the instrument is at a reasonable height for observing while seated.
     The Isostatic tripod doesn't fold down small. The redwood "azimuth" legs are one-piece, long (59 inches), and solid. They are held on the tripod with pivoting, black-anodized aluminum L-brackets. The "altitude" leg is made of aluminum with a sliding polyvinyl chloride (PVC) pipe nested inside and lockable with thumbscrew. The aluminum pipe attaches to the dense plastic heart of the tripod with a thumbscrew too. Collapsing the tripod means removing the altitude leg and folding together the azimuth legs, yielding two large pieces and some thumbscrews you should be careful not to misplace.
     The telescope is held in place with another long thumbscrew. Holding the telescope while threading the thumbscrew through the heart and L-brackets is risky, though that's what one is forced to do. It appears that a simple modification would permit telescopes with differently sized mounting bolts to be attached to the tripod.

Polar Alignment Accessories

     Once the ETX is equatorially mounted, it needs to be polar-aligned. Then the next order of business is finding objects for viewing. The compact design of the ETX makes seeing the pole through the finder a near impossibility. Finding objects at high declinations is challenging too.
     Tuthill and JMI offer solutions. Tuthill's Precision Polar Axis Finder was reviewed by Astronomy (May 1991) and was found to provide good polar alignment.
     The prototype of JMI's ETX Polar Finder ($49.95) was supplied with clear instructions for mounting. It is a 1x device consisting of a small-diameter sighting tube mounted on a hinged plate (so it folds out of the way for transport). I had no trouble seeing Polaris through the small tube and polar aligning for casual observing.
     Two right-angle finders are now on the market, from JMI and Tuthill, that make finding easier. The JMI unit is actually a 90 finder conversion kit ($69). Clear instructions explain the disassembly of the Meade finder and the reassembly using a new tube + diagonal mirror assembly. Fits were tight, and be careful not to cross-thread the old parts onto the new. The correct-view 5x21 Meade finder becomes reversed; up/down is correct but right/left is reversed.
     The new finder is low profile and is as elegant on the telescope as the original, but its use was not as pleasant. The mirror assembly interferes with the fork arm so that the celestial pole cannot be reached. Thus one is forced to use a separate polar axis alignment device or method, or file away plastic from the finder or fork arm to reach the pole.
     Because of the close quarters, in many telescope positions your nose or cheek is going to collide with the finder or the eyepiece when either is used. There is no provision for rotating the JMI finder's eyepiece out of the way to minimize this.
     Tuthill offers a 6x30 right angle finder ($125). The finder's mount must be machined out to fit the new finder tube (Tuthill does this for you). It makes for a close fit between finder and mount so that little adjustment is possible (or necessary, fortunately) and any burrs left from the machining must be removed (a fingernail will suffice).
     The Tuthill finder's eyepiece stands pretty tall, so cheek/nose interference could be a problem. However, by rotating the finder's prism assembly, it can be moved out of the way when the telescope is being used. The prism must be rotated slightly so the telescope can reach the celestial pole. The finder's eyepiece threading is so loose that it moves around, taking the crosshairs with it, and making precision pointing at high power impossible. A small piece of vinyl tape on the threads might minimize this problem.
     Finding can be done with computers, nowadays, and JMI has extended its MAX series of computers to the ETX. Installation of the encoders is the same for all of the computers. The right ascension encoder instructions were good, though there was a difference between the illustration and the words describing cable placement. There was no problem installing it with the Tuthill power indicator light already in place. The cable connecting the encoder (inside) to the socket (outside) is squeezed tightly by the base plate and could also be damaged when the telescope rests on it.
     The declination encoder installation was a bit more difficult, with more differences between the illustration and the instructions. Still, the hardware installed easily. Do have some double-sided foam tape available — the encoder shaft was a bit long and the tape, placed on the feet of the encoder support, served as a spacer. You will also need the tape to better attach the hook and loop material on the supplied vinyl cover. Follow the instructions carefully to set up the MAX for use on the sky. The supplied videotape was moderately helpful, with some useful general hints as well as specific examples.
     When I set up the MAX to use it, I had trouble getting the position error indication below 2.5. On one occasion I did manage 0.2, and the instructions say the error should not exceed 0.5. The instructions note that the error could be due to the mount's axes not being square. JMI's owner, Jim Burr, mentioned that placing a piece of tape over the right ascension encoder bolt might reduce the error and JMI may include that in future shipments. Also, one must use a sturdy tripod or pier. Otherwise flexure can lead to large error indications.
     I had an unexpected problem as well. On a humid (but no dewy) night I set up the NGC-microMAX for use. In a little while, it started indicating occasional errors, and then showed them continuously. I suspect the electronics didn't work well in the humidity, though JMI says they have never received similar reports.
     It doesn't look like this computer will work with my ETX. With numerous alignment attempts I managed to find my target in the eyepiece only once, and that was near one of my alignment stars and with a larger-than-desirable error message. If you get one, be sure the computer will work with your telescope, stand, and observing conditions.

Piggyback Camera Mounts

     A telescope as easy to use as the ETX just begs for a camera mount. Tuthill and JMI both offer one. The Tuthill unit ($48) uses a hose clamp to hold a Z-shaped (90 angles) aluminum piece (with 1/4-20 camera bolt) on the tube of the ETX. The base of the aluminum piece is not contoured to match the ETX tube. All the parts in contact with the tube are covered with liner to protect the tube's finish. Flexure is a real possibility with this approach.
     In contrast, the JMI camera mount ($59.95) is very elegant. It is a low profile, rubber coated single piece. A large-diameter thumbscrew holds the camera in place. A notable addition is the counterweight supplied to balance the camera on the telescope.

Dew Prevention and Stray Light Reduction

     Humid climates require an additional accessory, one that will prevent, or at least slow, the condensation of dew on the corrector lens of the telescope. Most observers also like to reduce stray light entering the telescope. Both of these requirements can be met with a dew cap. The dew cap is an open-ended cylinder that slips over the front of the telescope. Its length usually exceeds the aperture of the instrument.
     Tuthill and Jim Kendrick Studio Inc. offer dew caps. The Tuthill No Du cap ($56) uses the simple design, and its length is about the same as the ETX's tube length. It has a black felt inner lining that is very effective in a trapping stray light and a pleasing, astronomically themed outer cover. The dew cap slips tightly over the corrector lens cell of the ETX. It's too bad that it doesn't slide completely onto the tube, so that it could be carried easily as part of the telescope.
     The Kendrick Dew Remover for the ETX (Controller, $65 + 4-inch heater, $40) is an extension of his widely acclaimed line of dew removers. A flat, felt-lined dew cap rolls to fit around the circumference of the telescope tube. Nicely packaged heater tape can first be attached around the sky-end of the telescope with hook and loop material and then the dew cap is added. Another, lower-priced option has just become available. At press time, Clear Night Products has just introduced the TeleWrap/Dew Cap, which retails for $21.95. It is custom made for the ETX. It appears to be a viable, low-priced alternative.

Solar Filters

     An astronomer can double the amount of observing time available by adding the sun to his or her observing list. Tuthill and Thousand Oaks Optical offer safe solar filters suitable for observing sunspots and faculae (bright areas) on the sun's bright photosphere. Both manufacturers supply instructions on the safety and maintenance of their solar filters.
     The Tuthill filter ($48) uses his patented Solar Skreen aluminized mylar mounted on a soft plastic cell. The filter can be securely attached to the sky-end of the telescope by squeezing it on. A cool blue image appears in the eyepiece but I noticed a rather bright sky — probably the result of sunlight being scattered by the filter into the telescope. This is not dangerous, only distracting.
     The Thousand Oaks Type 2+ filter ($79) is deposited on a glass base and is mounted in a metal cell. It presents an orangish image of the sun. A single pinhole in the coating needed to be opaqued (a black permanent marker works, as noted in the instructions) and internal reflections were easily eliminated with a slight tilt of the filter cell on the telescope.

Miscellaneous Accessories

     A variety of other aids for the observer is available from Tuthill and JMI. If you purchase the ETX from Tuthill he includes his Power Saver Red LED Indicator Light for the drive. Otherwise, he will install it in yours for $50. A small hole is drilled in the base of the telescope and two leads are soldered to the electronics assembly inside the base.
     Vibrations induced during focusing or when making declination corrections with the slow motion knob can be a problem with the ETX. JMI has long offered focuser and declination motors and they have extended the line to the ETX. Their Motofocus lists for $99.95; purchased together the price is $169.90 (but includes only one dual hand control unit with a switch and wiring to operate both systems one at a time). I like both accessories.
     The Motodec does a good job moving the telescope in slow motion. It is a small assembly with a strong motor that fits on the far side of the fork arm with the declination knob. The coiled cord plugs into the motor unit and into the hand control when in use. Extra O-rings are supplied (and it is praiseworthy that JMI supplies extras of other small parts, such as set-screws, as a convenience to their customers). The installation instructions were marvelously easy to follow.
     The installation instructions for the Motofocus were also good, but must be followed carefully. A similar coiled cord runs between the motor and the hand controller. The plug's insulation was shaved so it could fit into the motor assembly. In place, the plug interferes with reaching the celestial pole. Also, the motor came loose from its connector to the focus assembly once when I was trying to remove the plug. Apparently it is press-fit on.
     A speed control is included on the hand unit but the motor won't start at low speed settings. It is fine at high speeds, but this may be too fast for some observers to bring the telescope to focus.
     Tuthill offers the "ETX How to Use Video Tape" for $29. It begins by assuming that you have read the Meade instruction manual (something I strongly advise) and offers some useful tricks and suggests modifications for an ETX observer. It is mainly a product listing and demonstration.
     JMI offers a foam-lined carrying case for the ETX ($109.95). It is die-cut to fit the telescope (with MAX encoders), its original accessories, a few extra eyepieces, and some JMI accessories such as the MAX computer. There isn't much room for additional accessories. It has a good hinge and the handle looks sturdy enough. The weight is not centered under the handle when it is loaded, unfortunately, and there's no shoulder strap.
     The Meade ETX telescope has spawned a number of accessories from a variety of manufacturers. Not all of those offered have been discussed here. Meade itself offers standard accessories like eyepieces, Barlow lenses, a T-adapter, an erecting prism, high-latitude tripod legs, and a carrying bag. Careful shopping will present a selection of accessories that will make the ETX an even better telescope for astronomers.