Meade Instruments Corporation
Telescopes · Binoculars · Microscopes


 
Meade Model 390 Refracting Telescope
 Meade Model 390 90mm (3.5") Altazimuth Refracting Telescope
  1. Introducing the Meade Model 390
    1. This Manual
    2. Standard Equipment
  2. Unpacking and Assembly
    1. Balancing the Telescope
    2. Alignment of the Viewfinder
  3. Using the Telescope
  4. Calculating Power
  5. Maintenance
    1. Cleaning
    2. Mount and Tripod Adjustments
  6. Specifications: Model 390
IMPORTANT NOTICE! Never use a telescope or spotting scope to look at the Sun! Observing the Sun, even for the shortest fraction of a second, will cause irreversible damage to your eye as well as physical damage to the telescope or spotting scope itself.

[ toc ] A. Introducing the Meade Model 390
The Model 390 is an easy-to-operate, high performance 90mm refracting telescope, intended for astronomical and terrestrial (land) observing. Equipped with a deluxe altazimuth mount and aluminum tripod, the telescope's motion is adjustable over a wide range for tracking celestial or land objects. Your telescope comes to you ready for adventure; it will be your companion in a universe of breathtaking landscapes, planets, galaxies, and stars.


Fig. 1: Meade Model 390: 90mm Altazimuth Refracting Telescope

1. Tripod legs
2. Altazimuth mount
3. Altitude flexible cable control
4. Azimuth flexible cable control
5. Azimuth lock
6. Azimuth base
7. Azimuth shaft bolt
8. Optical tube assembly
9. Optical tube saddle plate
10. Cradle rings
11. Cradle ring lock knobs
12. Diagonal mirror
13. Focuser
14. Focuser thumbscrew
15. Focus knobs
16. Eyepiece
17. Diagonal thumbscrew
18. 6 x 30 viewfinder
19. Telescope front dust cover
20. Viewfinder bracket thumbscrews
21. Viewfinder bracket
22. Dew shield
23. Objective lens cell
24. Altitude shaft acorn cap nut
25. Tripod leg Phillips-head fastener screws
26. Tripod leg bolt 1/2" nuts
27. Accessory shelf central mounting knob
28. Accessory shelf
29. Leg brace supports
30. Tripod leg lock knobs


[ toc ] 1. This Manual

These instructions detail the set-up, operation, specifications, and optional accessories of your Meade Model 390. In order that you may achieve maximum enjoyment of the instrument, we urge that you take a few minutes to read all of this manual before making first observations through the telescope. As you read this manual, the technical terms associated with telescopes will be made clear.

[ toc ] 2. Standard Equipment

—Complete optical tube assembly with multi-coated 90mm diameter objective lens, dew shield, cradle rings, viewfinder bracket, and 1.25" rack and pinion focuser. Lens focal length = 1000mm; f/11.

—Altazimuth mount with pre-attached heavy duty, continuously adjustable, aluminum tripod and leg braces.

—Accessories:

MA 25mm (40x) eyepiece (1.25" O.D. )
Diagonal mirror (1.25" O.D.)
Flexible cable controls for both telescope axes
Accessory shelf with mounting knob
6 x 30 viewfinder

[ toc ] B. Unpacking and Assembly (Numbers in brackets refer to Fig. 1.)

Your Meade Model 390 comes to you packaged almost entirely pre-assembled. You will find upon opening the giftbox that there are two compartments within that contain the optical tube assembly and the tripod with equatorial mount. The accessories described above will be located within compartments custom-cut into the styrofoam block inserts. (References herein, e.g., (6)—are to Fig.1 unless otherwise specified.)

—Remove and identify the telescope's Standard Equipment listed in Section A.2., above.

—The three tripod lock knobs (30) have been removed from the bottom section of each tripod leg to insure safe arrival of the tripod assembly. To install, thread in each tripod lock knob into the threaded hole located at the right side of each of the three gray colored castings (see illustration, below) at the bottom of each tripod leg. Tighten the tripod lock knob only to a "firm feel" to avoid damage to the tripod caused by overtightening.

—Spread the tripod legs (1) to full extension so that the leg braces (29) are taut (should one of the tripod leg braces slip out of the center triangle fastener, merely reposition the brace and slide it back into position). Adjust the tripod with the attached mount (2) to the desired height by loosening the tripod lock knobs and extend the sliding inner section of each tripod leg; then tighten each knob.

—Remove the mounting knob from the round accessory shelf (28). Place the accessory shelf on top of the center triangle leg brace fastener of the tripod so that the threaded stud protruding from the bottom of the shelf passes through the hole in the center. Then replace and tighten the accessory shelf mounting knob (27).

—Attach the flexible cable controls (3) and (4). These cable controls are secured in place with a firm tightening of the thumbscrew located at the end of each cable.

—The viewfinder bracket (21) comes pre-attached to the optical tube, but the viewfinder (18) is shipped separately. Place the viewfinder into the viewfinder bracket rings by backing off the thumbscrews. Then center the viewfinder in both bracket rings using the three thumbscrews (20) on each bracket ring. Orient the viewfinder so its front objective lens is pointing in the same direction as the main telescope's objective lens (23).

—While firmly holding the optical tube (8), position it onto the optical tube saddle plate (9), with the midpoint of the optical tube's length lying roughly in the center of the saddle plate. Then slide the cradle rings (10) over the saddle plate of the mount. Tighten the cradle lock knobs (11) to a firm feel. Do not overtighten these knobs. Make sure the focuser mechanism is on the same side as the slow-motion controls.

—Insert the diagonal mirror (12) into the focuser (13), and tighten the focuser thumbscrew (14), to secure the diagonal mirror.

—Insert the MA25mm eyepiece (16) into the diagonal mirror, and tighten the diagonal thumbscrew (17) to secure the eyepiece.

The telescope is now fully assembled. Before it can be properly used, however, the telescope must be balanced and the viewfinder aligned.

[ toc ] 1. Balancing the Telescope

In order for the telescope to move smoothly on its mechanical axes, it must first be balanced on the saddle plate. All motions of the altazimuth telescope (more on this later) take place by moving about these two axes; altitude (up-and-down motion), and azimuth (side-to-side motion) separately or simultaneously. To obtain a fine balance of the telescope, follow the method below:

—Loosen the cradle ring lock knobs (11) so that the main tube (8) in the cradle rings (10) slides easily up-or-down in the cradle rings. Move the main tube in the cradle rings until it is balanced on the saddle (9). Re-lock the knobs (11).

The telescope is now properly balanced.

[ toc ] 2. Alignment of the Viewfinder

The wide field of view provided by the 6 x 30mm viewfinder permits easy object sighting prior to observation in the higher-power main telescope. The 6 x 30 Viewfinder (18) must be attached to the viewfinder bracket (21) as seen in Fig. 1. In order for the viewfinder to be functional, however, it must be aligned to the main telescope, so that both the viewfinder and main telescope point at the same position in the sky. With this simple alignment performed, finding objects is greatly facilitated, since you will first locate an object in the wide-field viewfinder, then you will look in the eyepiece of the main telescope for a detailed view. To align the viewfinder follow these steps:

—Remove the telescope front dust cover (19), and the dust covers of the viewfinder.

—Place the low-power (MA25mm) eyepiece into the focuser of the main telescope.

—Unlock the Azimuth lock (5) so that the telescope turns on both axes. (Note: The altitude axis is a clutched mechanism that does not require locking or unlocking to allow movement.) To move the Model 390 in altitude (up or down), merely grasp the rear portion of the telescope optical tube assembly (8) and apply a small amount of force in the up or down direction desired. Point the main telescope at some well-defined land object (e.g., the top of a telephone pole) at least 200 yards distant, and re-lock the azimuth lock (5). Turn the flexible cable controls, (3) and (4), to center the object in the telescopic field.

—With the front of the viewfinder already centered in the front bracket ring, look through the viewfinder and loosen or tighten, as appropriate, one or more of the rear viewfinder bracket ring thumbscrews (26) until the viewfinder's crosshairs are likewise centered on the object previously centered in the main telescope.

—Check this alignment on a celestial object, such as a bright star or the Moon, and make any refinements necessary, using the method outlined above.

With this alignment performed, objects first located in the wide-field of the viewfinder will also be centered in the main telescope's field of view. (Note: The viewfinder presents an image which is upside-down; this orientation is customary in astronomical viewfinders.)

[ toc ] C. Using the Telescope

With the telescope assembled, and balanced as described above, you are ready to begin observations. Decide on an easy-to-find object such as the Moon, if it is visible, or a distant land object to become accustomed to the functions and operations of the telescope. For the best results during observations, follow the suggestions below:

—To center an object in the main telescope, loosen the telescope's Azimuth lock (5) . The telescope can now turn on its axes. Use the aligned viewfinder to first sight-in on the object you wish to observe; with the object centered on the viewfinder's crosshairs, re-tighten the Azimuth lock. Then turn the Altitude and Azimuth flexible cable controls (3) and (4) for any fine centering adjustments necessary.

Note: It is possible to "run out" of adjustment when using the flexible cable controls (3) and (4). If this occurs, turn the flexible cable control until the Altitude or Azimuth tangent assembly is in the middle of its travel. Re-center the object you wish to observe by releasing the Azimuth lock (5) and move the telescope up, down, or side-to-side by grasping the rear portion of the telescope optical tube assembly (8) and apply a small amount of force in the direction desired. Turn the Altitude and Azimuth flexible cable controls (3) and (4) for fine centering.

—If you have purchased an assortment of eyepieces, always start an observation session with a lower power eyepiece (e.g., MA 25mm eyepiece); get the object well-centered in the field of view and sharply focused. Then try the next step up in magnification. If the image starts to become fuzzy as you work into higher magnifications, then back down to a lower power; the atmospheric steadiness is not sufficient to support high powers at the time you are observing. Keep in mind that a bright, clearly resolved but smaller image will show far more detail than a dimmer, poorly resolved larger image. The MA 25mm eyepiece included with the Model 390 presents a wide field of view, ideal for general observing of land objects, clusters of stars, nebulae, and galaxies. It is also probably the best eyepiece to use in the initial finding and centering of any object.

—Once centered, the object can be focused by turning one of the knobs of the focusing mechanism (15). You will notice that an astronomical object in the field of view will begin to slowly move across the eyepiece field. This motion is caused by the rotation of the Earth on its axis, although the planets and stars, are, for practical purposes, fixed in their positions in the sky. The platform on which the telescope is sitting ( the Earth) rotates once every 24 hours under these objects. To keep astronomical objects centered in the field of the telescope, simply turn one or both of the Altitude and Azimuth flexible cable controls (3) and (4). Objects will appear to move through the field more rapidly at higher powers.

—Avoid touching the eyepiece while observing through the telescope. Vibrations resulting from such contact will cause the image to move. Likewise, avoid observing sites where ground-based vibrations may resonate the tripod. Viewing from the upper floors of a building may also introduce image movement.

—You should allow a few minutes to allow your eyes to become "dark adapted" before attempting any serious astronomical observations. Use a red filtered flashlight to protect your night vision when reading star maps or inspecting the components of the telescope.

—Avoid setting up the telescope inside a room and observing through an open window (or worse yet, a closed window). Images viewed in such a manner may appear blurred or distorted due to temperature differences between inside and outside air. Also, it is a good idea to allow your telescope a chance to reach the ambient (surrounding) outside temperature before starting an observing session.

—Avoid viewing objects low on the horizon. Objects will appear better resolved with far greater contrast when viewed higher in the sky. Also, if images appear to "shimmer" in the eyepiece, reduce power until the image steadies. This condition is caused by air turbulence in the upper atmosphere.

The Meade Model 390 may be used for a lifetime of rewarding terrestrial and astronomical observing, but basic to your enjoyment of the telescope is a good understanding of the instrument. Read the above instructions carefully until you understand all of the telescope's parts and functions. One or two observing sessions will serve to clarify these points forever in your mind.

The number of fascinating objects visible through your Meade refractor is limited only by your own motivation. Astronomical software such as Meade's AstroSearch, or a good star atlas such as the Meade Star Charts will assist you in locating many interesting celestial objects. These objects would include:

  • Cloud belts across the surface of the planet Jupiter.

  • The 4 major satellites of Jupiter, visible in rotation about the planet, with the satellite positions changing each night.

  • Saturn and its famous ring system, as well as several satellites of Saturn, much fainter than the major satellites of Jupiter.

  • The Moon: A veritable treasury of craters, mountain ranges and fault lines. The best contrast for viewing the Moon is during its crescent phase. The contrast during the full Moon phase is low due to the angle of illumination.

  • Deep-Space: Nebulae, galaxies, multiple star systems, star clusters hundreds of such objects are visible through the Model 390.

  • Terrestrial objects: Your Meade Model 390 may be used for high-resolution land viewing. In this case note that the diagonal mirror results in an image which is reversed left-for-right, but which is correctly oriented up and down. For a fully-corrected image, the optional Meade #928 45° Erect-Image Roof Prism is required. Terrestrial observations should almost always be made using a low-power eyepiece (50X or less), for bright sharp images. Beyond the 50X-limit, images may appear ill-defined due to the fact that the images are being viewed through the thickest and most turbulent part of the atmosphere, unlike astronomical observations made by pointing the telescope up and through a thinner atmosphere.

[ toc ] D. Calculating Power

The power, or magnification, of the telescope depends on two optical characteristics: the focal length of the main telescope and the focal length of the eyepiece used during a particular observation. For example, the focal length of the Model 390 telescope is fixed at 1000mm. To calculate the power in use with a particular eyepiece, divide the focal length of the eyepiece into the focal length of the main telescope. For example, using the MA 25mm eyepiece supplied with the Model 390, the power is calculated as follows:

Power = 1000mm ÷ 25mm= 40x

Meade Instruments manufactures several types of eyepiece designs that are available for your telescope. The type of eyepiece ("SP" Super Plössl, etc.) has no bearing on magnifying power but does affect such optical characteristics as field of view, flatness of field, eye-relief, and color correction.

The maximum practical magnification is determined by the nature of the object being observed and, most importantly, by the prevailing atmospheric conditions. Under very steady atmospheric "seeing," the Model 390 may be used at powers up to about 250X on astronomical objects. Generally, however, lower powers of perhaps 75X to 175X will be the maximum permissible, consistent with high image resolution. When unsteady air conditions prevail (as witnessed by rapid "twinkling" of the stars), extremely high-power eyepieces result in "empty magnification," where the object detail observed is actually diminished by the excessive power. Under such conditions a planet may appear as a featureless fuzzy orb of bright light.

Accessory eyepieces are available both to increase and decrease the operating eyepiece power of the telescope. If the Model 390 is used on a regular basis, a selection of four to five eyepieces is a worthwhile investment to get the best performance from your telescope. For example, an eyepiece assortment of focal lengths 32mm or 40mm, 25mm, 12.5mm, 9mm, and 6mm yields a magnifying range of 31x or 25x, 40x, 80x, 111x, and 167x respectively. A high quality Barlow Lens, such as the Meade #126 2x Telenegative Barlow Lens, serves to double the power of each of these eyepieces. To use the Barlow Lens, insert the #126 unit into the telescope's focuser first, then insert the diagonal mirror, followed by an eyepiece; the power thus obtained is then double the power obtained when the eyepiece is used alone. For example, the MA 25mm eyepiece, when used in conjunction with the #126 2x Telenegative Barlow Lens yields 80X.

[ toc ] E. Maintenance

[ toc ] 1. Cleaning

As with any quality instrument, lens or mirror surfaces should be cleaned as infrequently as possible. Multi-coated lens surfaces, in particular, should be cleaned only when absolutely necessary. In all cases avoid touching any lens surface. A little dust on the surface of a lens or mirror causes negligible loss of performance and should not be considered reason to clean the surface. When lens cleaning does become necessary, use a camel's hair brush or compressed air gently to remove dust. If the telescope's dust cover is replaced after each observing session, cleaning of the optics will rarely be required. Note: remove the dew shield (22) to access the objective lens (23) for cleaning.

[ toc ] 2. Mount and Tripod Adjustments

Every Meade Model 390 Altazimuth mount and tripod is factory inspected for proper fit and function prior to shipment. It is unlikely that you will need to adjust or tighten these parts after receipt of the telescope. However, if the instrument received unusually rough handling in shipment, it is possible that some of these assemblies can be loose. To make adjustments you will need 1/2", 11/16", and/or 3/4" socket or adjustable end wrenches, and a Phillips-head screwdriver.

The Altazimuth mount has two main areas that can be adjusted: A loose Altitude shaft can be tightened by turning the Altitude shaft 3/4" acorn cap nut (24) clockwise to a firm feel. A loose Azimuth base (6), can be tightened by turning the 11/16" Azimuth shaft bolt (7), that is located underneath the mount and in between the three tripod legs, clockwise to a firm feel. Note that overtightening of any of the nuts or bolts can inhibit the smooth rotating action of the axes and gears, and may result in stripping the threads.

The tripod legs have 1/2" nuts (26), and Phillips-head screws (25) that may have backed off; these may also be tightened to a firm feel for the most sturdy performance of the telescope.

[ toc ] F. Specifications: Model 390

Objective (main) lens focal length: 1000mm
Objective lens diameter: 90mm (3.54")
Focal ratio: f/11
Mounting : Altazimuth

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