Meade ETX-90EC User Manual

4.5 (6)
Meade ETX-90EC User Manual

Instruction Manual

ETX-90EC Astro Telescope

ETX-125EC Astro Telescope

Meade Instruments Corporation

20

2

5

3

4

19

18

6

(on left fork

17

7

(on both sides)

16

8

9

21

15

14

13

10

12

11

CONTENTSz

3

® The name “Meade,” the Meade logo, and “ETX” are trademarks registered with the U.S. Patent Office and in principal countries throughout the world. All rights reserved.

© 2000 Meade Instruments Corporation.

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-

1

 

START

A

GUIDE

 

B

 

 

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.

2

C

D

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.

3

NOTE:The

 

telescope has

 

rotational hard

 

stops in the

F

horizontal and

 

vertical axes to

 

prevent damage to

 

the telescope. See

 

Quick Tips, page 6,

G

for more

E

information.

 

 

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.

4

G E

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.

5

H

Slew Speed:

Fast

Medium

Moderate

Slow

I

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

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

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.

INTRODUCTION

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. With 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) at 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

OPTIONAL ACCESSORIES, page 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 Electronic Controller Functions, page 6.

Parts List

In keeping with the ETX philosophy of elegant simplicity, an ETX telescope is virtually completely assembled at the Meade factory. 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.

Assembly Instructions

CHAPTER

Assembly of both ETX model telescopes requires eight (user-

1

supplied) AA-size batteries and the following steps:

1.a. ETX-90EC 8 x 21mm Viewfinder: Slide the eyepiece end of the viewfinder through the front of the viewfinder bracket (1, Fig. 3).

1

ETX-90EC Viewfinder

2

ETX-125EC Right-Angle Viewfinder

b.ETX-125EC 8 x 25mm Right-Angle Viewfinder: Slide the 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 8.

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).

1

2

3

6

4

5

Basic assembly of either ETX model is now complete.

6

 

 

CHAPTER

 

TELESCOPE FEATURES

1

Quick Tips

 

 

Rotational Limits: The telescope base and fork mount are

 

 

designed with internal “rotational limit stops.” Thehorizontal

 

 

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 be yond 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 Viewing: 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 observations 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 counterclockwise 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 counterclockwise 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 “down” when the control is horizontal (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 connector, and two auxiliary ports (see OPTIONAL ACCESSORIES, page 16).

5

2

3

4

1

2

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.

AUX (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.

GETTING STARTED

7

Indicator Lights (2, Fig. 6): Four red LED (Light Emitting Diode) lights are used to indicate the current slew speed.

1

 

 

Fast

7

 

 

 

 

Medium

2

 

 

 

Moderate

6

 

 

3

 

Slow

5

 

 

 

4

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.

 

 

 

 

 

 

Light 1

 

 

 

 

On

Light 2

 

 

 

 

Blinking

 

 

 

 

 

 

 

 

Light 3

 

 

 

 

Off

 

 

 

 

Light 4

 

 

 

 

 

 

 

 

 

 

 

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 OPTIONAL ACCESSORIES, page 17).

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).

CHAPTER

1

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).

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 OPTIONAL ACCESSORIES, page 18) to move the 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.

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

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

7. Press any key on the Electronic Controller and the telescope slews momentarily in the vertical and horizontal directions to test the motors.

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

lights 2, 3, and 4 turn off.

9.Use the four arrow keys (1, Fig. 6) to slew the telescope to the desired object. To change the slew speed, press the SPEED key.

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).

8

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

THE VIEWFINDER

CHAPTER

 

 

 

 

 

 

1

 

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 Erect-

 

 

Image 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 25 mm Right-Angle Viewfinder:

 

 

Standard equipment with the ETX-125EC, the 8 x 25mm Right-

 

 

Angle Viewfinder has 8-power magnification and an aperture of

 

 

25mm. This viewfinder presents a correctly oriented image up-

 

 

and-down, but is reversed left-for-right.

 

3

 

 

 

 

2

 

 

 

 

 

 

 

 

 

 

 

 

4

 

 

 

 

 

 

 

 

 

 

 

ETX-125EC

 

 

 

 

 

 

 

 

 

 

1

5

 

 

 

 

 

 

2

6

 

 

 

ETX-90EC

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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

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.

NOTE: Do not overtighten the alignment screws. When 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 eyepiece’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)

 

1

 

 

 

 

View through the

 

View through the

viewfinder

 

telescope eyepiece

 

 

 

(after

alignment)

2

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.

Observing Tip: 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 e yepiece; 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.

Chapter 2:TELESCOPE FUNDAMENTALS

9

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 e yepiece 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 resolution.

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,

CHAPTER

different eyepiece focal lengths are used to achieve different

2

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:

 

 

 

Telescope Focal Length

 

Power =

____________________

 

Eyepiece Focal Length

 

 

 

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

1900mm

Power = ________ = 73X 26mm

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

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 Tripod (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).

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