Meade ETX-90EC User Manual

Instruction Manual

ETX-90EC Astro Telescope ETX-125EC Astro Telescope

Meade Instruments Corporation

1 2

Features of the ETX-90EC and ETX-125EC are identical, with the exception of the size of optical tube and the type of viewfinder included as standard equipment.

(on left fork arm)

(on both sides)

Fig. 1: The ETX-90EC Astro Telescope.

1. Eyepiece

2. Viewfinder:

ETX-90EC: 8x21mm Erect-Image Viewfinder ETX-125EC: 8 x 25mm Right-Angle Viewfinder

3. Eyepiece holder thumbscrew

4. 90° eyepiece holder

5. Optical tube:

6. Vertical (or Declination) lock

7. Fork-mount attachment screws

8. Fork arm

9. Focus knob

10. Horizontal (or Right Ascension) lock

ETX-90EC: 90mm clear aperture ETX-125EC: 127mm clear aperture

11. Computer control panel

12. Drive base

13. Hole cover for optional tripod legs (2)

14. Right Ascension (R.A.) setting circle

15. 1/4-20 photo tripod adapter block

16.Flip-mirror control knobs

17. Photo port

18. Declination (Dec.) setting circle (on left fork arm)

19. Viewfinder alignment screws

20. Viewfinder bracket

21. Electronic controller with attached coil cord

CONTENTS

WARNING!

Never use a Meade®ETX®AstroTelescope 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.

If you are anxious to use your ETX Astro Telescope for the first time, b e fore a thorough reading of this instruction manual, see the Quick-Start Guide on page 4.

CAUTION: Use care to install batteries as indicated by the battery compart m e n t . Follow battery manufacturers precautions. Do not install batteries backward or mix new and used batteries.Do not mix battery t y p e s . If these precautions are not followed,batteries may explode, catch fire, or leak. Improperly installed batteries void your Meade warranty.

Quick-Start Guide . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Chapter 1: Getting Started . . . . . . . . . . . . . . . . . .5

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

The Electronic Controller . . . . . . . . . . . . . . . . . .5

Parts Listing . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Assembly Instructions . . . . . . . . . . . . . . . . . . . .5

Telescope Features . . . . . . . . . . . . . . . . . . . . . . . . .6

Quick Tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

Telescope Controls . . . . . . . . . . . . . . . . . . . . . .6

Computer Control Panel . . . . . . . . . . . . . . . . . . .6

Electronic Controller Functions . . . . . . . . . . . . . .6

First Observations . . . . . . . . . . . . . . . . . . . . . . .7

Observing with the Electronic Controller . . . .7

The Viewfinder . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Focusing the Viewfinder . . . . . . . . . . . . . . . . . . .8

Aligning the Viewfinder . . . . . . . . . . . . . . . . . . . .8

Using the Viewfinder . . . . . . . . . . . . . . . . . . . . .8

Chapter 2: Telescope Fundamentals . . . . . . . . .9

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Choosing an Eyepiece . . . . . . . . . . . . . . . . . . . .9

Understanding Magnification . . . . . . . . . . . . . . .9

Telescope Mountings . . . . . . . . . . . . . . . . . . . . .9

Terrestrial Observing . . . . . . . . . . . . . . . . . . . .10

Astronomical Observing . . . . . . . . . . . . . . . . . .10

Sidereal Rate . . . . . . . . . . . . . . . . . . . . . . .10

Slew Speeds . . . . . . . . . . . . . . . . . . . . . . .10

The Electronic Controller . . . . . . . . . . . . . . . . . . . .11

Modes of Operation . . . . . . . . . . . . . . . . . . . . .11

Using the Mode Screws . . . . . . . . . . . . . . .11

Electronic Controller Modes . . . . . . . . . . . .11

Chapter 3: Polar Alignment . . . . . . . . . . . . . . . .12

Celestial Coordinates . . . . . . . . . . . . . . . . . . . .12

Locating the Celestial Pole . . . . . . . . . . . . . . . .12

Polar Alignment Procedure . . . . . . . . . . . . . . . .12

Chapter 4: Observing . . . . . . . . . . . . . . . . . . . . . . 14

Objects in Space . . . . . . . . . . . . . . . . . . . . . . . . . .14

The Moon . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

Planets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

Deep-Sky Objects . . . . . . . . . . . . . . . . . . . . . .14

Photography with Both ETX Models . . . . . . . . . . . .15

Chapter 5: Optional Accessories . . . . . . . . . . .16

Chapter 6: Maintenance and Servicing . . . . .19

General Maintenance . . . . . . . . . . . . . . . . . . . .19

Storage and Transport . . . . . . . . . . . . . . . . . . .19

Inspecting the Optics . . . . . . . . . . . . . . . . . . . .19

Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . .19

Meade Customer Service . . . . . . . . . . . . . . . . .20

Telescope Specifications . . . . . . . . . . . . . . . . .21

Appendix A: Tracking Motor Speed . . . . . . . .22

Appendix B: Helpful Charts . . . . . . . . . . . . . . . .23

Latitude Chart for Major Cities of the World . . .23

Star Locator . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Appendix C: Precise Polar Alignment;

Setting Circles . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24

Precise Polar Alignment . . . . . . . . . . . . . . . . . .24

Setting Circles . . . . . . . . . . . . . . . . . . . . . . . . .24

Appendix D: Road Map to the Stars . . . . . . . .25

Appendix E:You and the Universe . . . . . . . . .26

QUICK-START GUIDE

QUICK-

START GUIDE

Remove the ETX from its packaging and place it on a sturdy surface. Place the eyepiece (A) and viewfinder (B) into their appropriate positions on the telescope and tighten the appropriate attachment screws to a firm feel only.

Flip the Power Switch (E) on the computer control panel to the ON position. The lights flicker on the Electronic Controller. Press any key and the motors briefly move the telescope. The Electronic Controller is now operational.

Slew Speed:

Fast Medium Moderate Slow

Securely place the ETX on its side and remove the battery compartment cover (C) from the underside of the drive base. Insert eight (user-supplied) AA-size batteries into the battery compartment (D) in the proper orientation. Replace the cover and return the telescope to an upright position.

Verify that the computer control panel power switch (E) is in the OFF position. Remove the Electronic Controller (F) from the packing materials and plug it into the HBX port (G). Tighten the vertical and horizontal locks (6 and 10, Fig. 1), then remove the dust cover from the end of the telescope tube.

NOTE:The telescope has rotational hard stops in the horizontal and

vertical axes to prevent damage to the telescope. See Quick Tips, page 6, for more information.

Use the arrow keys (H) of the Electronic Controller to move the telescope up and down and/or left and right. To change the telescope’s slew speed, press the SPEED key (I). The indicator lights signify the speed, with the upper light showing the highest speed. Each press slows the speed down one level, then cycles back to the highest speed.

NOTE: Before

Sight along the side of the telescope’s main tube to locate an object. Practice using the arrow keys on the Electronic Controller to center an object in the telescope’s field of view. Use the telescope’s focus knob (9, Fig. 1) to bring the object into focus.

observing, verify that the flip-mirror control (16, Fig. 1) is in the “up” position. See Flip-Mirror Control, page 6, for more information.

INTRODUCTION

Chapter 1: GETTING STARTED

CHAPTER

Fig.3: Installation of the Viewfinder.

A Meade ETXAstro Telescope is an extremely versatile, highresolution imaging system that, with advanced features similar to larger and more specialized telescopes, can be used by casual observers and serious astronomers alike. Wi t h pushbutton controls, automatic tracking of celestial objects (with one of the optional tripods), and diffraction-limited imaging, an ETX telescope may be all the telescope ever required by many terrestrial and astronomical observers.

As a first telescope, the ETX-90EC or ETX-125EC reveals nature in an ever-expanding level of detail: observe the feather structure of a bird from 50 yards or study the rings of the planet Saturn from a distance of 800 million miles. Beyond the Solar System observe nebulae, star clusters, galaxies, and other deep-sky objects. Both telescopes are instruments fully capable of growing with your interest.

Your Meade ETX Astro Telescope is one of the most revolutionary telescope systems ever developed. Read this manual thoroughly to take full advantage of the telescope’s numerous advanced features.

This manual provides instructions for the following products:

• ETX-90EC Astro Telescope

• ETX-125EC Astro Telescope

The Electronic Controller

Control of both ETX model telescopes is through pushbutton operation of the standard-equipment Electronic Controller (Fig. 2). Nearly all functions of the telescope are accomplished through the Electronic Controller with just a few button pushes:

• Move the telescope on two axes (up-and-down or left-and-right) any of 4 drive speeds for precise tracking of astronomical or terrestrial objects.

• Mount the telescope in the polar mode for fully automatic tracking of celestial objects using the optional #880 (ETX–90EC), #881 (ETX-125EC) Table Tripod, or #883 Deluxe Field Tripod (see

O P T I O N A L AC C E S S O R I E S

17).

• When in the polar mode, switch the motor drive between northern and Southern Hemisphere operation for observing from anywhere in the world.

A detailed description of the functions and operation of the Electronic Controller is found in E l e c t ronic Contro l l e r Functions, page 6.

, page

Fig.2: Electronic Controller.

Assembly Instructions

Assembly of both ETX model telescopes requires eight (usersupplied) AA-size batteries and the following steps:

1. a.

ETX-90EC

of the viewfinder through the front of the viewfinder bracket (1, Fig. 3).

8 x 21mm Viewfinder: Slide the eyepiece end

ETX-90EC Viewfinder

ETX-125EC Right-Angle Viewfinder

ETX-125EC

front cell end of the right-angle viewfinder through the rear of the viewfinder bracket (2, Fig. 3).

You may need to unthread the six alignment screws slightly to fit the viewfinder through the bracket. With the viewfinder in place, tighten (to a firm feel only)the six alignment screws against the viewfinder tube. To align the viewfinder, see page

2. Remove the SP26mm eyepiece (1, Fig. 1) from its container and place it in the eyepiece holder (4, Fig. 1). Tighten the

thumbscrew (3, Fig. 1) to a firm feel only.

3. The telescope’s battery compartment (6, Fig. 4) is at the

bottom of the drive base. Place the telescope securely on its side as shown in Fig. 4. Open the battery compartment by simultaneously depressing the two release latches (4, Fig. 4) and pulling the battery cover (5, Fig. 4) away from the drive base. Insert eight AA-size batteries into the battery compartment, oriented as shown on the battery mounting board. Put the cover back in place.

4. Place the telescope in an upright position on a flat surface.

Be certain that the power switch on the computer control panel (1, Fig. 5) is in the OFF position. Plug the coil cord for the Electronic Controller into the HBX port (3, Fig. 5).

8 x 25mm Right-Angle Viewfinder: Slide the

Parts List

In keeping with the ETX philosophy of elegant simplicity, an ETX telescope is virtually completely assembled at the Meade f a c t o r y. Getting the telescope ready for first observations requires only a few minutes. When first opening the packing box, note carefully the following parts:

• The ETX Astro Telescope with fork-mount system.

• Electronic Controller with attached coil cord.

• Viewfinder, packed in a separate small box.

• Super Plössl (SP) 26mm eyepiece, packed in a plastic storage container, in a separate small box.

• Hex-wrench set (2 wrenches), packed with the manual.

The viewfinder is packed separately from the main telescope to avoid the possibility of the viewfinder slipping in its bracket and scratching the viewfinder tube during shipment.

Fig.4: Bottom view of an ETX showing eight AA-size batteries mounted inside the battery compartment. (1) High-latitude tripod leg hole; (2) Drive base; (3) Alternate tripod leg hole; (4) Release latches; (5) Battery compartment cover; (6) Battery compartment.

Basic assembly of either ETX model is now complete.

GETTING STARTED

CHAPTER

TELESCOPE FEATURES

QuickTips

• Rotational Limits: The telescope base and fork mount are designed with internal “rotational limit stops.” The horizontal limit stop prevents the telescope from rotating more than 630° to avoid damage to the internal wiring. The vertical limit stop prevents the viewfinder from contacting the fork mount when the telescope is pointed upward just past 90° and prevents the optical tube from contacting the base if pointed downward more than 30°. Do not force the telescope to

move beyond these stops or damage to the telescope will result.

• Vertical Lock;Declination Setting Circle:The vertical lock knob (6, Fig. 1) is a knurled knob located on the fork arm to the right of the focus knob (9, Fig. 1). Mounted beneath the knob is a circular scale with no numbers. Do not confuse this scale with the Dec setting circle (18, Fig. 1) on the opposite fork arm which has a number scale used to locate astronomical objects.

• A Note on Indoor V i ew i n g : While casual, low-power observations may be made with the telescope through an open or closed window, the best observing is always done outdoors. Temperature differences between inside and outside air and/or the low quality of most home window glass can cause blurred images through the telescope. Do not

expect high-resolution imaging under these conditions.

Telescope Controls

An important array of features and manual controls facilitates operation of an ETX telescope. Be sure to become acquainted

with all of these controls before attempting observa t i o n s through the telescope.

Horizontal Lock (10, Fig. 1): Controls manual horizontal rotation of the telescope while sitting upright as shown in Fig.1. Turning the horizontal lock c o u n t e r c l o ck w i s e unlocks the telescope, enabling it to be freely rotated by hand about the horizontal axis. Turning the horizontal lock clockwise prevents the telescope from being rotated manually, but engages the horizontal motor drive clutch for Electronic Controller operation. When polar aligned, the horizontal lock serves as the Right Ascension, or R.A. lock (see Right Ascension, page 12).

Vertical Lock(6, Fig. 1): Controls manual vertical movement of the telescope while sitting upright as shown in Fig. 1. Turning the vertical lock c o u n t e r c l o ckwise unlocks the telescope enabling it to be freely rotated by hand about the vertical axis. Turning the vertical lock clockwise (to a firm feel only) prevents the telescope from being moved manually, but engages the vertical motor drive clutch for Electronic Controller operation. When polar aligned, the vertical lock serves as the Declination, or Dec lock (see Declination, page 12).

Focus Knob (9, Fig. 1): Causes a finely-controlled internal motion of the telescope’s primary mirror to achieve precise image focus. An ETX can be focused on objects from a distance of about 11.5 ft (ETX-90EC) or 15 ft (ETX-125EC) to infinity. Rotate the focus knob clockwise to focus on distant objects; counterclockwise to focus on near objects.

Flip-Mirror Control (16, Fig. 1): Both ETX models include an internal optically-flat mirror. With the flip-mirror control in the “up” position, as shown in Fig. 1, light is diverted at a 90° angle to the eyepiece. Alternately, with the flip-mirror control in the “down” position, light proceeds straight through the telescope and out the photo port (17, Fig. 1) for telephoto or astronomical photography using the optional #64 T-Adapter, or for observing with the optional #932 45° Erecting Prism (see

OPTIONAL

ACCESSORIES

, page 17).

NOTE: The flip-mirror control is in the “up” position when the control is vertical (perpendicular to the telescope tube). It is “ d ow n ” when the control is hori zontal (parallel with the telescope tube).

Computer Control Panel

The computer control panel (Fig. 5) of the ETX-90EC and ETX–125EC models include a connector for either the standard-equipment Electronic Controller or the optional #497 Autostar Computer Controller, an external power supply c o n n e c t o r, and two auxiliary ports (see

O P T I O N A L

ACCESSORIES

, page 16).

ON/OFF (1, Fig. 5): When the ON/OFF switch is moved to the ON position, the red power indicator light (5, Fig. 5) illuminates and power is supplied to the Electronic Controller and to the telescope’s motor drive.

AU X (2, Fig. 5): Two identical auxiliary ports provide connections for current and future Meade accessories.

CAUTION:Using products other than standard Meade accessories may cause damage to the telescope’s internal electronics and may void the Meade warranty .

HBX (3, Fig. 5): The HBX (handbox) port is designed to accept

the plug from the coil cord of the Electronic Controller or the optional #497 Autostar Computer Controller.

12v (4, Fig. 5): The 12v connector is designed to accept an external power supply such as the optional #541 AC adapter or the #607 Power Cord (see

OPTIONAL ACCESSORIES

, page 18). When one of these alternate powering options is used, the internal batteries are disconnected from the power circuit.

NOTE: Always remove the batteries if they are not to be used for a long period of time.

Electronic Controller Functions

The Electronic Controller provides the observer with the means to control the telescope motors from a compact handbox. The Electronic Controller (Fig. 6) has soft-touch keys designed to have a positive feel, even through gloves. Primary functions of the Electronic Controller are to move (slew) the telescope, indicate the slew speed, and to operate the optional #1244 (ETX-90EC) or #1247 (ETX-125EC) Electric Focuser (see OPTIONAL ACCESSORIES, page 18). Other functions are also possible when using the MODE key (see Electronic Controller Modes, page 11 and APPENDIX A, page 22).

Arrow Keys (1, Fig. 6): The four arrow keys slew the telescope in four directions (i.e., up-and-down or left-and-right) at any one of four slew speeds (see SPEED Key, page 7).

Important Note: While using the arrow keys to slew to an object, when reversing direction there may be a slight pause as the telescope motors compensate for the reversal of the internal gears.

2 3 4

Fig. 5: Computer Control Panel. (1) ON/OFF switch; (2) Auxiliary ports; (3) Handbox port; (4) 12v connector; (5) Power indicator light.

Indicator Lights (2, Fig. 6): Four red LED (Light Emitting

GETTING STARTED

CHAPTER

Slow

Fig.6: Electronic Controller. (1) Arrow Keys; (2) Indicator

Lights; (3) SPEED Key; (4) Coil Cord; (5) MODEKey; (6) OUT Key; (7) IN Key.

Diode) lights are used to indicate the current slew speed.

Fast

Medium Moderate Slow

NOTE:For purposes of this manual, the lights are identified as 1 through 4, with 1 being the top light and 4 the bottom light.

Indicator Light Key Light No. Light Status

The procedures in this manual identify the status of the four indicator lights in a box to the left of the appropriate step. They are depicted as on, blinking, or off, depending on the mode at that point.

SPEED Key (3, Fig. 6): The SPEED key is used to change the speed at which the telescope slews when the arrow keys are pressed. Each press of the SPEED key changes the slew speed to the next slower setting. If the controller is already on the slowest slew speed (light 4), pressing the SPEED key cycles back to the highest speed (light 1). Slew speeds are signified by the indicator lights (2, Fig. 6).

Fast

Medium

MODE Key (5, Fig. 6): Pressing and holding the MODE key

puts the Electronic Controller into the Mode function (see

Electronic Controller Modes, page 11). OUT Key (6, Fig. 6): The OUT key is used in conjunction with

the optional #1244 (ETX-90EC) or #1247 (ETX-125EC) Electric Focuser (see focus point outward.

IN Key (7, Fig. 6): The IN key is used in conjunction with the optional Electric Focuser to move the focus point inward.

OPTIONAL ACCESSORIES

Light 1 Light 2 Light 3 Light 4

Moderate

, page 18) to move the

First Observations

Unthread the metal dust cap from the front lens of the telescope (counterclockwise), and the ETX may now be used for terrestrial (land) observing.

NOTE:The dust cap should be replaced after each observing session and the power turned off to the telescope. Verify that

On Blinking Off

any dew that might have collected during the observing session has evaporated prior to replacing the dust cap.

With the standard-equipment SP 26mm eyepiece inserted in the eyepiece holder, the telescope is operating at the following power (see Understanding Magnification, page 9):

• ETX-90EC 48X

• ETX-125EC 73X Objects viewed through the eyepiece are correctly oriented up-

and-down in the telescope but are reversed left-for-right. Image orientation is discussed further in Terrestrial Observing, page 10. The flip-mirror control (16, Fig. 1) must be in the “up” position in order to observe an image through the telescope’s eyepiece (see Flip-Mirror Control, page 6).

For the ultimate viewing experience, become familiar with the features of your ETX telescope and the functions of the Electronic Controller. Upon completing this chapter make first observations of a simple land object several hundred yards in the distance— perhaps a telephone pole or a building. Locate objects first in the viewfinder before viewing them in the main telescope (see Aligning the Viewfinder, page 8). Practice focusing on the object using the focus knob (9, Fig. 1) and centering the object in the eyepiece using the Electronic Controller arrows keys (1, Fig. 6).

Observing with the Electronic Controller

With the Electronic Controller in the factory pre-set “Alt/Az” (vertical-horizontal) mode, the Electronic Controller arrow keys permit pushbutton movements (slewing) of the telescope. To move the telescope using the Electronic Controller:

1. Set the telescope on a level and stable surface, or mount to the Meade #883 Deluxe Field Tripod (see

ACCESSORIES

2. Insert a low-power eyepiece (e.g., SP 26mm) into the eyepiece holder (4, Fig. 1) and tighten the eyepiece thumbscrew (3, Fig. 1).

3. Tighten the vertical and horizontal locks (6 and 10, Fig. 1).

4. Verify that the power switch (1, Fig. 5) on the telescope’s computer control panel is OFF.

5. Plug in the Electronic Controller coil cord (4, Fig. 6) to the HBXport (3, Fig. 5) on the computer control panel.

6. Flip the power switch to ON. The power indicator

7. Press any key on the Electronic Controller and the

8. When the test is complete, light 1 comes on steady;

9. Use the four arrow keys (1, Fig. 6) to slew the

10. Fine-adjust the position of the object with the Electronic Controller arrow keys so that it is centered in the viewfinder. The object is now ready to be viewed through the telescope’s eyepiece.

Observing Tip:If the Electronic Controller has previously been placed in the polar mode (see Electronic Controller Modes, page 11) and Alt/Az operation is desired, flip the telescope power switch to OFF and perform steps 6, 7, and 8 above.The telescope is now in the Alt/Az mode. This procedure does not work if one of the mode screws has been removed (see Using the Mode Screws, page 11).

, page 17).

light (5, Fig. 5) on the computer control panel comes on and all four Electronic Controller indicator lights (2, Fig. 6) blink rapidly.

telescope slews momentarily in the vertical and horizontal directions to test the motors.

lights 2, 3, and 4 turn off.

telescope to the desired object. To change the slew speed, press the SPEED key.

O P T I O N A L

GETTING STARTED

CHAPTER

THE VIEWFINDER

As with most astronomical telescopes, both ETX model telescopes present a fairly narrow field of view to the observer. As a result it is sometimes difficult to locate and center objects in the telescope’s field of view. The viewfinder, by contrast, is a low-power, wide-field sighting scope with crosshairs that let you easily center objects in the eyepiece of the main telescope’s field of view.A telescope’s viewfinder is a tremendous aid in the location of faint astronomical objects before observation is made through the telescope’s eyepiece.

ETX-90EC 8 x 21mm Erect-Image Viewfinder:

Standard equipment with the ETX-90EC, the 8 x 21mm ErectImage Viewfinder has 8-power magnification and an aperture of 21mm. This viewfinder presents a correctly oriented image both up-and-down and left-to-right.

ETX-125EC 8 x 25mm Right-Angle Viewfinder:

Standard equipment with the ETX-125EC, the 8 x 25mm RightAngle Viewfinder has 8-power magnification and an aperture of 25mm. This viewfinder presents a correctly oriented image upand-down, but is reversed left-for-right.

ETX-125EC

telescope. Gently tighten the six alignment screws. Proceed with Aligning the Viewfinder.

ETX-125EC

Turn the focus ring (2, Fig. 7) at the base of the viewfinder eyepiece (3, Fig. 7) in either direction until a sharp focus is reached.

Aligning the Viewfinder

In order for the viewfinder to be useful, it must first be aligned with the main telescope, so that both the viewfinder and the main telescope are pointing at precisely the same location. To align the viewfinder follow this procedure:

1. The viewfinder bracket (5, Fig. 7) includes six alignment

screws (4 and 6, Fig. 7). Turn the three rear alignment screws (6, Fig. 7) so that the viewfinder tube is roughly centered within the viewfinder bracket.

N OT E : Do not ove rtighten the alignment screw s. W h e n tightening one screw it may be necessary to loosen one or both of the two other alignment screws.

2. Using the SP26mm eyepiece, point the main telescope at some easy-to-find, well-defined land object, such as the top of a telephone pole. Center the object precisely in the e y e p i e c e ’s field of view, then tighten the vertical and horizontal locks (6 and 10, Fig. 1) so that the object does not move (1, Fig. 8).

(before

alignment)

ETX-90EC

Fig.7: The Viewfinder. (1) Front lens cell; (2) Knurled lock-

ring (ETX-90EC) or focus ring (ETX-125EC); (3) Viewfinder eyepiece; (4) Front alignment screws; (5) Viewfinder bracket; (6) Rear alignment screws.

Focusing the Viewfinder

Both ETX model viewfinders are factory pre-focused to objects located at infinity. Individual eye variations may require that the viewfinder be re-focused. To check the focus look through the viewfinder. Point the viewfinder at a distant terrestrial (land) object such as a telephone pole or light pole. If the viewfinder image is not in sharp focus, follow the procedure for your type of telescope.

ETX-90EC

1. If the viewfinder is mounted in the viewfinder bracket (5,Fig.

7), remove it by slightly unthreading the six alignment screws (4 and 6, Fig. 7) until it can slip easily out of the bracket.

2. Loosen the knurled lock-ring (2, Fig. 7) located near the viewfinder’s front lens cell (1, Fig. 7). Unthread this ring (counterclockwise, as seen from the eyepiece-end of the viewfinder) by several turns.

3. Look through the viewfinder and focus on a distant object. Slowly rotate the front lens cell in one direction or the other, until the object appears sharp. One or two rotations of the lens may have a significant effect on image focus.

4. Lock the focus in place by threading the knurled lock-ring clockwise up against the viewfinder’s lens cell.

5. Place the viewfinder into the viewfinder bracket on the main

View through the

viewfinder

alignment)

View through the

telescope eyepiece

(after

Fig.8: Aligning the Viewfinder.

3. While looking through the viewfinder, turn one or more of the three front viewfinder alignment screws (4, Fig. 7), until the crosshairs of the viewfinder point at precisely the same position as the view through the eyepiece of the main telescope (2, Fig. 8).

Re-check that the viewfinder’s crosshairs and the main telescope are now pointing at precisely the same object. The viewfinder is now aligned to the main telescope. Unless the alignment screws are disturbed or the viewfinder jarred, the viewfinder should remain aligned indefinitely.

Using the Viewfinder

To locate any object, terrestrial or astronomical, first center the object in the crosshairs of the viewfinder; the object should also then be centered in the field of view of the main telescope.

O b s e rving T i p: If higher observing magnifications are intended, first locate, center, and focus the object using a lowpower eyepiece (e.g., SP 26mm eyepiece). Remove the lowpower eyepiece and replace it with a higher-power eyepiece; the object should still be centered in the field of view. Objects are much easier to locate and center at lower powers; higher powers are employed simply by changing eyepieces.

9Chapter 2:TELESCOPE FUNDAMENTALS

INTRODUCTION

Both ETX model telescopes can be used for immediate observation right out of the box. However, becoming familiar with the fundamentals of a telescope makes subsequent viewing easier and more rewarding.

Choosing an Eyepiece

The function of a telescope’s eyepiece is to magnify the image formed by the telescope’s main optics. Each eyepiece has a focal length (expressed in millimeters, or “mm”). The smaller the focal length, the higher the magnification. Low power eyepieces offer a wide field of view, bright high-contrast images, and eye relief during long observing sessions. To find an object with a telescope it is always best to start with a low power eyepiece such as the SP 26mm supplied with both ETX models. When the object is located and centered in the eyepiece, switch to a higher power eyepiece to enlarge the image as much as practical for prevailing seeing conditions.

Lower power eyepieces are recommended for terrestrial viewing. Haze, heat waves, and particulate matter in the air distort images when using higher powers.

For astronomical observing a selection of several different eyepieces is recommended. For general observing of the Moon and planets, low to medium powers are preferred. For deep-sky objects such as nebulae and galaxies, higher powers may be needed for the best view if conditions permit.

NOTE: Viewing conditions vary widely from night to night. Turbulence in the air, even on an apparently clear night, can distort images. If an image appears fuzzy and ill-defined, back off to a lower power eyepiece for a better resolved image (see Fig.9).

Understanding Magnification

The magnification, or power, at which a telescope is operating is determined by two factors: the focal length of the telescope and the focal length of the eyepiece employed.

Telescope Focal Length is the distance that light travels inside the telescope before reaching a focus. In the mirror-lens design of both ETX models, however, this focal length is, in effect, compressed by the telescope’s secondary mirror, so that a long effective focal length is housed in the short ETX optical tube. For example, the ETX-90EC’s focal length is 1250mm, or about 49”. This means that if the ETX–90EC were a classical refractingtype of telescope, its optical tube would be more than four feet long instead of the ETX–90EC's compact 11” tube length.

Eyepiece Focal Length is the distance light travels inside the eyepiece before reaching focus. Focal length is usually printed on the side of the eyepiece. Both ETX models are supplied with at least one eyepiece as standard-equipment. For instance, the Super Plössl (SP) 26mm eyepiece supplied with the ETX-90EC and ETX-125EC has a focal length of 26mm. “Super Plössl” refers to the optical design of the eyepiece, a design specifically intended for high-performance telescopes and one which yields a wide, comfortable field of view with extremely high image r e s o l u t i o n .

Technical note to the advanced amateur astronomer: The SP 26mm eyepiece supplied with the Meade ETX-90ECand ETX-125EC is a special low-profile version of the standard Meade SP 26mm eyepiece which is about 1/4” (6mm) shorter than the standard eyepiece. This low-profile SP 26mm is designed to harmonize with the ultracompact scale of both ETX models and utilizes the exact same optics as the standard SP 26mm eyepiece. The SP 26mm low-profile eyepiece is not parfocal with other eyepieces in the SP series (i.e., the eyepiece requires re-focusing when it is interchanged with other SP eyepieces).

Calculating Magnification: On a telescope, such as the ETX, different eyepiece focal lengths are used to achieve different magnifications, from low to high. The standard-equipment SP 26mm eyepiece yields 48X (“48-power”) on the ETX-90EC and 73X on the ETX-125EC. A variety of powers are obtainable with the addition of optional eyepieces as well as the #126 2X Barlow Lens which double the power of the eyepiece employed (see

OPTIONAL ACCESSORIES

, page 16).

Use this formula to calculate the magnification obtained with a given eyepiece:

Too Much Power: The most common mistake of the beginning observer is to overpower the telescope by using high magnifications, which typical atmospheric conditions and the telescope’s aperture cannot reasonably support. A smaller but bright and well-resolved image is far superior to one that is larger, but dim and poorly resolved (see Fig. 9). Powers above 300X (ETX–90EC) or 500X (ETX–125EC) should be employed only under the steadiest atmospheric conditions.

Most observers should have 3 or 4 eyepieces plus the #126 2X

Barlow Lens to achieve the full range of reasonable magnifications possible

with both ETX models.

Telescope Mountings

The telescope mounting or mount is the mechanical means that causes the telescope’s optical tube to move in various directions. Telescope mounts are of two basic types.

Altazimuth (Alt/Az) mounts permit motion of the telescope tube in vertical (altitude) and horizontal (azimuth) directions. Both ETX models incorporate an altazimuth mount (as shown in Fig. 10). For all terrestrial applications and for casual astronomical observing, the telescope operates very well in the altazimuth configuration. The telescope may be placed on a rigid tabletop or on the optional Meade #883 Deluxe Field T ripod (see page 17) to provide a secure, variable-height, altazimuth observing platform. To track objects, either terrestrial or astronomical, with the telescope in the altazimuth configuration, press the arrow keys of the Electronic Controller (see page6).

Power =

Example: The power obtained with the ETX-125EC using the SP 26mm eyepiece is:

Power =

Telescope Focal Length

____________________

Eyepiece Focal Length

1900mm

________

26mm

= 73X

CHAPTER

Fig.9: Example of too much magnification (Galaxy M51).

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