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Meade ETX-90EC Astro Telescope Instruction Manual
WARNING! Never use the Meade ETX-90EC Astro Telescope to look at the Sun! Looking at or near the Sun will cause instant and irreversible damage to your eye. Eye damage is often painless, so there is no warning to the observer that damage has occurred until it is too late. Do not point the telescope or its viewfinder at or near the Sun. Do not look through the telescope or its viewfinder as it is moving. Children should always have adult supervision while observing.
[ toc ] General Maintenance

The ETX-90EC is a precision optical instrument designed to yield a lifetime of rewarding applications. Given the care and respect due any precision instrument, the ETX-90EC will rarely, if ever, require factory servicing or maintenance. Maintenance guidelines include:
  1. Avoid cleaning the telescope's optics: a little dust on the front surface of the telescope's correcting lens causes virtually no degradation of image quality and should not be considered reason to clean the lens.
  2. When absolutely necessary, dust on the front lens should be removed with gentle strokes of a camel hair brush or blown off with an ear syringe (available at any pharmacy). Do not use a commercial photographic lens cleaner.
  3. Organic materials (e.g., fingerprints) on the front lens may be removed with a solution of 3 parts distilled water to 1 part isopropyl alcohol. A single drop of biodegradable dishwashing soap may be added per pint of solution. Use soft, white facial tissues and make short, gentle strokes. Change tissues often.

    CAUTION: Do not use scented, colored, or lotioned tissues or damage could result to the optics.
  4. In the very rare situation where cleaning the inside surface of the corrector lens becomes necessary, unthread the lens cell located at the front of the main tube. The entire correcting lens and secondary mirror system is mounted in this cell. The lens cleaner solution described in step 3 may be used to clean the inside surface of the lens.

    CAUTION: Do not touch the aluminized circular surface of the secondary mirror with a finger, a tissue, or any other object. Scratching of the mirror surface will almost certainly result.

    NOTE: When cleaning the inside surface of the correcting lens, leave the lens mounted in its metal cell throughout the process. Do not remove the lens from its metal housing or else optical alignment of the lens will be lost, necessitating a return of the telescope to the Meade factory.

  5. If the ETX-90EC is used outdoors on a humid night, telescope surfaces may accumulate water condensation. While such condensation does not normally cause any damage to the telescope, it is recommended that the entire telescope be wiped down with a dry cloth before being packed away. Do not, however, wipe any of the optical surfaces. Rather, simply allow the telescope to sit for some time in warm indoor air, so that the wet optical surfaces can dry unattended. In addition, the dust cap should not be placed back on to the optical tube until the telescope is thoroughly dry.
  6. If the ETX-90EC is not to be used for an extended period, perhaps for one month or more, it is advisable to remove the eight AA-size batteries from inside the drive base. Batteries left installed for prolonged periods may leak, causing damage to the telescope's electronic circuitry (see Assembly Instructions).
  7. The super-gloss anodized finish of the ETX-90EC's deep-violet optical tube fades if left in direct sunlight for prolonged periods.
  8. Do not leave the ETX-90EC telescope outdoors on a warm day or inside a sealed car for an extended period of time; excessive ambient temperatures can damage the telescope's internal lubrication and electronic circuitry.
  9. A set of two (English-format) hex wrenches is provided with each ETX-90EC Astro Telescope. These wrenches are used as follows:
    • Small wrench (.05"): Use the small wrench to tighten the set-screws of any knobs which may loosen (e.g., the focus knob or flip-mirror control knob).
    • Medium wrench (1/16"): This wrench is used to detach the viewfinder bracket from the telescope's rear-cell.

[ toc ] Storage and Transport

When not in use, store the telescope in a cool, dry place. Do not expose the instrument to excessive heat or moisture. It is best to store the telescope in its original box with the vertical and horizontal locks (6 and 10, Fig. 1) in the unlocked positions. If shipping the telescope, use the original box and packing material to protect the telescope during shipment.

When transporting the telescope, take care not to bump or drop the instrument; this type of abuse can damage the optical tube and/or the objective lens. It is highly recommended to use the #765 Soft Carrying Bag or #774 Hard Carrying Case to transport the telescope (see OPTIONAL ACCESSORIES).

[ toc ] Inspecting the Optics

A Note About the "Flashlight" Test: If a flashlight or other high-intensity light source is pointed down the main telescope tube, the view (depending upon the observer's line of sight and the angle of the light) may reveal what appears to be scratches, dark or bright spots, or uneven coatings, giving the appearance of poor quality optics. These effects are only seen when a high intensity light is transmitted through lenses or reflected off the mirrors, and can be seen on any high quality optical system, including giant research telescopes.

The optical quality of a telescope cannot be judged by the "flashlight" test; the true test of optical quality can only be conducted through careful star testing.

[ toc ] Troubleshooting

The following suggestions may be helpful if there are difficulties with operation of the Electronic Controller or ETX-90EC telescope.

The power indicator light does not come on or there is no response when pressing the Electronic Controller arrow keys:

  • Verify that the computer control panel power switch (1, Fig. 4) is in the ON position.
  • Verify that the Electronic Controller cord (4, Fig. 5) is firmly connected to the HBX port (3, Fig. 4).
  • If using internal power (batteries), verify that the batteries are installed correctly and that they have sufficient charge (see Assembly Instructions).

    NOTE: If the batteries are getting low on charge there will be a marked difference in the slew speed. The speed indicator lights may also flash and the speed may change. If any of these symptoms occurs, turn the power off and replace the batteries.

  • If using an external power source, verify that it is properly connected between the 12 volt connector (4, Fig. 4) and either a wall plug (AC source) or a car lighter (DC source).
  • If the Electronic Controller does not respond to commands, place the power switch to OFF and then back to ON.
  • If the telescope does not slew after power is applied or if the motor quits or stalls, verify that there are no physical obstructions that would impede telescope movement.
  • If all physical obstacles are removed and the telescope still does not move properly, turn off the power and unplug the Electronic Controller. Plug the Electronic Controller back in and turn the power back on.

Unable to see an image through the eyepiece:

  • Confirm that the lens cover has been removed from the telescope.
  • Confirm that the flip-mirror control (16, Fig. 1) is in the "up" position if using the eyepiece holder (4, Fig. 1) so that light is directed to the eyepiece (1, Fig. 1). Confirm that the flip-mirror control is in the "down" position if using the #932 Erecting Prism or doing photography with the ETX-90EC (see Telescope Controls and PHOTOGRAPHY WITH THE ETX-90EC).

Object appears in the viewfinder but not in the eyepiece:

  • The viewfinder is not properly aligned with the telescope (see THE VIEWFINDER).

Slew speed does not change when the SPEED key is pressed or the telescope moves slowly even though the fast slew speed is chosen:

  • Verify that only one light is lit on the Electronic Controller. If more than one light is on or blinking then the Mode function is active. Exit the Mode function by pressing and holding the MODE key until only one light is on (see Electronic Controller Modes).
  • The battery power may be low (see Assembly Instructions.)

Telescope does not track a celestial object:

Images through the eyepiece appear unfocused or distorted:

  • The magnification used may be too high for the seeing conditions. Back off to a lower power eyepiece (see Understanding Magnification).
  • If inside a warm house or building, move outside. Interior air conditions may distort terrestrial or celestial images, making it difficult, if not impossible, to obtain a sharp focus. For optimal viewing, use the telescope outside in the open air instead of observing through an open or closed window or screen.
  • If viewing a land object on a warm day, heat waves will distort the image (see Terrestrial Observing).
  • For clear viewing of objects, turn the focus knob (9, Fig. 1) slowly since the "in-focus" point of a telescope is precise. Turning the focus knob too quickly may cause the focus point to pass without notice.
  • The optics within the telescope need time to adjust to the outside ambient temperature to provide the sharpest image. To "cool down" the optics, set the telescope outside for 10 to 15 minutes before observing begins.

Telescope moves off a terrestrial object while observing:

Telescope does not move past a certain point:

  • The built-in vertical or horizontal rotational "stops" may have been reached (see Rotational Limits).

Telescope pauses when changing slew direction:

A terrestrial object appears reversed left-for-right:

  • An eyepiece in the standard 90° observing position (4, Fig. 1) yields this image orientation. To view a correctly oriented image, the optional #932 Erecting Prism is required (see OPTIONAL ACCESSORIES.

[ toc ] Meade Customer Service

If you have a question concerning the ETX-90EC, call the Meade Instruments Customer Service Department at (949) 451-1450, or fax at (949) 451-1460. Customer Service hours are 8:30 AM to 4:30 PM, Pacific Time, Monday through Friday. In the unlikely event that the ETX-90EC requires factory servicing or repairs, write or call the Meade Customer Service Department first, before returning the telescope to the factory, giving full particulars as to the nature of the problem, as well as your name, address, and daytime telephone number. The great majority of servicing issues can be resolved by telephone, avoiding return of the telescope to the factory.

[ toc ]
Specifications: ETX-90EC Telescope
Optical designMaksutov-Cassegrain
Primary mirror diameter96mm (3.78")
Clear aperture90mm (3.5")
Focal length1250mm
Focal ratio (photographic speed)f/13.8
Near focus (approx)11.5 ft (3.5m)
Resolving power1.3 arc secs
Super multi-coatingsstandard
Limiting visual stellar magnitude (approx)11.7
Image scale1.16°/inch
Maximum practical visual power325X
Optical tube dimensions (dia. x length)10.4cm x 27.9cm (4.1" x 11")
Secondary mirror obstruction (dia.; %)27.9mm (1.1"); 9.6%
Telescope mountingfork type; double tine
Setting circle diametersDec: 3.5"; RA: 7"
Input voltage12-volts DC
Hemispheres of operationnorth and south, switchable
Electronic controller4 speed, both axes
   AltitudeUHMW Polyethylene
   Tube bodyaluminum
   Mountinghigh-impact ABS, aluminum-reinforced
   Primary mirrorPyrex® glass
   Correcting lensBK7 optical glass, Grade-A
Telescope dimensions38cm x 18cm x 22cm (15" x 7" x 9")
Telescope net weight: (incl. Electronic Controller & batteries)3.5kg (7.8 lbs)
Telescope shipping weight5.6kg (12.3 lbs)

Appendix A: Tracking Motor Speed

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