Celestron AstroMaster LT Series Telescopes Instruction Manual

Figure 1-1 AstroMaster LT 70AZ Refractor (AstroMaster LT 60AZ refractor similar)

Diagram showing the refractor telescope components:

1. Objective Lens
2. Telescope Optical Tube
3. Star Pointer Finderscope
4. Eyepiece
5. Diagonal
6. Focus Knob
7. Pan Handle
8. Accessory Tray
9. Tripod
10. Azimuth Lock
11. Alt-Az Mount
12. Dovetail Mounting Bracket

Figure 1-2 AstroMaster LT 76 AZ Newtonian

Diagram showing the Newtonian telescope components:

1. Star Pointer Finderscope
2. Eyepiece
3. Telescope Optical Tube
4. Primary Mirror
5. Pan Handle
6. Azimuth Lock
7. Accessory Tray
8. Tripod
9. Alt-Az Mount
10. Dovetail Mounting Bracket
11. Focus Knob

Assembly

Setting Up the Tripod

This section covers the assembly instructions for your AstroMaster LT telescope. Your telescope should be set up indoors the first time so that it is easy to identify the various parts and familiarize yourself with the correct assembly procedure before attempting it outdoors.

Each AstroMaster LT comes in one box. The pieces in the box are: optical tube with attached sky pointer, Alt-Az mount with attached pan handle, 10 mm eyepiece – 1.25", 20 mm eyepiece – 1.25", mirror diagonal 1.25" (for 60AZ and 70 AZ), "The Sky" Level 1 CD-ROM.

1. Remove the tripod from the box. The tripod comes preassembled so that the set up is very easy.

2. Stand the tripod upright and pull the tripod legs apart until each leg is fully extended and then push down slightly on the tripod leg brace. The very top of the tripod is called the tripod head.

3. Install the tripod accessory tray onto the tripod leg brace (center of the tripod head).

4. Insert the cut-out in the center of the tray (flat side facing down) to match the center of the tripod leg brace and push down slightly. The ears of the tray should appear as shown.

5. Rotate the tray until the ears are under the leg brace support of each leg and push slightly; they will lock in place. The tripod is now completely assembled.

6. Extend the tripod legs to the desired height. The lowest level is 24" (61cm) and extends to 41" (104cm). Unlock the tripod leg lock knob at the bottom of each leg and pull the legs out to the desired height, then lock the knob securely. A fully extended tripod is shown.

7. The tripod will be the most rigid and stable at the lowest height.

Moving the Telescope Manually

The AstroMaster LT Alt-Az mount is easy to move wherever you want to point it. The up and down (altitude) is controlled by the pan handle. The side-to-side (azimuth) is controlled by the azimuth lock. The pan handle and the azimuth lock are both loosened by turning the handle and lock counterclockwise. When loose, you can find your objects easily and then lock the controls by turning them clockwise.

Attaching the Telescope Tube to the Mount

The telescope optical tube attaches to the mount via a dovetail slide bar mounting bracket at the top of the mount. The mounting bar is attached along the bottom of the telescope tube. Before attaching the optical tube, make sure that the pan handle and azimuth lock are fully locked. Then put the dovetail bracket in the horizontal position. This will ensure that the mount does not move suddenly while attaching the telescope optical tube. Also, remove the objective lens cap (refractor) or the front opening cap (Newtonian).

To mount the telescope tube:

1. Remove the protective paper covering the optical tube.
2. Loosen the mounting knob and the mounting safety screw on the side of the dovetail mounting platform so they do not protrude into the mounting platform.
3. Slide the dovetail mounting bar into the recess on the top of the mounting platform.
4. Tighten the mounting knob on the dovetail mounting platform to hold the telescope in place.
5. Hand tighten the mounting platform safety screw until the tip touches the side of the mounting bracket.

NOTE: Never loosen any of the knobs on the telescope tube or mount other than the pan handle and azimuth locks.

Installing the Diagonal & Eyepieces (Refractor)

The diagonal is a mirror assembly that diverts the light at a right angle to the light path of the refractor. This allows you to observe in a position that is more comfortable than if you looked straight through. Also, the diagonal can be rotated to any position which is most favorable for you.

To install the diagonal and eyepieces:

1. Insert the small barrel of the diagonal into the 1.25" eyepiece adapter of the focuser tube on the refractor. Make sure the two thumbscrews on the eyepiece adapter do not protrude into the focuser tube before installation and the plug up cap is removed from the eyepiece adapter.
2. Put the chrome barrel end of one of the eyepieces into the diagonal and tighten the thumb screw. Ensure the thumb screw is not protruding into the diagonal before inserting the eyepiece.
3. The eyepieces can be changed to other focal lengths by reversing the procedure in step 2 above.

Installing the Eyepieces on the Newtonians

The eyepiece (or ocular) is an optical element that magnifies the image focused by the telescope. Without the eyepiece, it would be impossible to use the telescope visually. Eyepieces are commonly referred to by focal length and barrel diameter. The longer focal length (i.e., the larger the number) the lower the eyepiece magnification (i.e., power). Generally, you will use low-to-moderate power when viewing. For more information on how to determine power, see the section on "Calculating Magnification". The eyepiece fits directly into the focuser of the Newtonians.

To attach the eyepieces:

1. Make sure the thumbscrews are not protruding into the focuser tube. Then, insert the chrome barrel of the eyepieces into the focuser tube (remove the plug up cap of the focuser first) and tighten the thumbscrews.
2. The eyepieces can be changed by reversing the procedure as described above.

Telescope Basics

A telescope is an instrument that collects and focuses light. The nature of the optical design determines how the light is focused. Some telescopes, known as refractors, use lenses, and other telescopes, known as reflectors (Newtonians), use mirrors.

Refractor Telescopes

Developed in the early 1600s, the refractor is the oldest telescope design. It derives its name from the method it uses to focus incoming light rays. The refractor uses a lens to bend or refract incoming light rays, hence the name. Early designs used single element lenses. However, the single lens acts like a prism and breaks light down into the colors of the rainbow, a phenomenon known as chromatic aberration. To get around this problem, a two-element lens, known as an achromat, was introduced. Each element has a different index of refraction allowing two different wavelengths of light to be focused at the same point. Most two-element lenses, usually made of crown and flint glasses, are corrected for red and green light. Blue light may still be focused at a slightly different point.

Figure 3-1: A cutaway view of the light path of the Refractor optical design, showing light passing through a lens.

Newtonian Reflector Telescopes

A Newtonian reflector uses a single concave mirror as its primary. Light enters the tube traveling to the mirror at the back end. There, light is bent forward in the tube to a single point, its focal point. Since putting your head in front of the telescope to look at the image with an eyepiece would keep the reflector from working, a flat mirror called a diagonal intercepts the light and points it out the side of the tube at right angles to the tube. The eyepiece is placed there for easy viewing.

Newtonian Reflector telescopes replace heavy lenses with mirrors to collect and focus the light, providing much more light-gathering power for the money spent. Because the light path is intercepted and reflected out to the side, you can have focal lengths up to 1000mm and still enjoy a telescope that is relatively compact and portable. A Newtonian Reflector telescope offers such impressive light-gathering characteristics you can take a serious interest in deep space astronomy even on a modest budget. Newtonian Reflector telescopes do require more care and maintenance because the primary mirror is exposed to air and dust. However, this small drawback does not hamper this type of telescope's popularity with those who want an economical telescope that can still resolve faint, distant objects.

Figure 3-1: Cutaway view of the light path of the Newtonian, showing light reflecting off a primary mirror and then a secondary mirror.

Image Orientation

The image orientation changes depending on how the eyepiece is inserted into the telescope. When using a star diagonal with refractors, the image is right-side-up, but reversed from left-to-right (i.e., mirror image). If inserting the eyepiece directly into the focuser of a refractor (i.e., without the diagonal), the image is upside-down and reversed from left-to-right (i.e., inverted).

Newtonian reflectors produce a right-side-up image but the image will appear rotated based on the location of the eyepiece holder in relation to the ground.

Figure 3-3: Illustrates image orientation: left shows image as seen with the unaided eye & using erecting devices on refractors & Newtonians; middle shows image reversed from left to right, as viewed using a Star Diagonal on a refractor; right shows inverted image, normal with Newtonians & as viewed with eyepiece directly in a refractor.

Focusing

To focus your refractor or Newtonian telescope, simply turn the focus knob located directly below the eyepiece holder. Turning the knob clockwise allows you to focus on an object that is farther than the one you are currently observing. Turning the knob counterclockwise allows you to focus on an object closer than the one you are currently observing.

Note: If you wear corrective lenses (specifically glasses), you may want to remove them when observing with an eyepiece attached to the telescope. However, when using a camera, you should always wear corrective lenses to ensure the sharpest possible focus. If you have astigmatism, corrective lenses must be worn at all times.

Aligning the Finderscope

The Star Pointer is the quickest and easiest way to point your telescope exactly at a desired object in the sky. It's like having a laser pointer that you can shine directly onto the night sky. The Star Pointer is a zero magnification pointing tool that uses a coated glass window to superimpose the image of a small red dot onto the night sky. While keeping both eyes open when looking through the Star Pointer, simply move your telescope until the red dot, seen through the Star Pointer, merges with the object as seen with your unaided eye. The red dot is produced by a light-emitting diode (LED); it is not a laser beam and will not damage the glass window or your eye. The star pointer is powered by a long life 3-volt lithium battery (#CR1620).

Like all finderscopes, the Star Pointer must be properly aligned with the main telescope before it can be used. The alignment procedure is best done at night since the LED dot will be difficult to see during the day.

To align the Star Pointer finderscope:

1. Turn on the Star Pointer by turning the switch to the "on" position.
2. Locate a bright star or planet and center it in a low power eyepiece in the main telescope.
3. With both eyes open, look through the glass window at the alignment star. If the Star Pointer is perfectly aligned, you will see the red LED dot overlap the alignment star. If the Star Pointer is not aligned, take notice of where the red dot is relative to the bright star.
4. Without moving the main telescope, turn the Star Pointer's two adjustment screws until the red dot is directly over the alignment star. Experiment to determine which way each screw moves the red dot.
5. The Star Pointer is now ready for use. Always turn the power off after you have found an object. This will extend the life of both the battery and the LED.

Note: Your battery may be installed already. If not, open the battery compartment with a thin coin or screwdriver. Put the battery in with the "+" sign facing out. Then put the battery compartment back on. If you ever need to replace the battery, it is a 3-volt lithium type # CR 1620.

Note: The above description applies basically for astronomy. If your finderscope is aligned properly, you can use it for terrestrial applications also. The finderscope acts like a sighting tube. The red dot may be difficult to see in the daytime but the dot will let you align objects before looking through the main telescope optics and can be quite helpful.

Calculating Magnification

You can change the power of your telescope just by changing the eyepiece (ocular). To determine the magnification of your telescope, simply divide the focal length of the telescope by the focal length of the eyepiece used. The formula is:

Magnification = Focal Length of Telescope (mm) / Focal Length of Eyepiece (mm)

For example, using the 20mm eyepiece that came with your telescope, and assuming the AstroMaster LT 60AZ has a focal length of 700mm, dividing 700 by 20 yields a magnification of 35 power.

Although the power is variable, each instrument under average skies has a limit to the highest useful magnification. The general rule is that 60 power can be used for every inch of aperture. For example, the AstroMaster LT 60AZ is 2.4" in diameter. Multiplying 2.4 by 60 gives a maximum useful magnification of 144 power. Most observing is done in the range of 20 to 35 power for every inch of aperture (48 to 84 times for the AstroMaster LT 60AZ).

Determining Field of View

Determining the field of view is important if you want to get an idea of the angular size of the object you are observing. To calculate the actual field of view, divide the apparent field of the eyepiece (supplied by the eyepiece manufacturer) by the magnification. The formula is:

True Field = Apparent Field of Eyepiece / Magnification

Using the example from the previous section, with a 20mm eyepiece having an apparent field of view of 50°, dividing by the magnification of 30 power yields an actual field of 1.7°.

To convert degrees to feet at 1,000 yards (useful for terrestrial observing), multiply by 52.5. For the example, 1.7° multiplied by 52.5 produces a linear field width of 89 feet at a distance of one thousand yards.

General Observing Hints

When working with any optical instrument, there are a few things to remember to ensure you get the best possible image.

• Never look through window glass. Glass found in household windows is optically imperfect and may vary in thickness, affecting focus. In most cases, you will not achieve a sharp image, and in some cases, you may see a double image.
• Never look across or over objects that are producing heat waves, such as asphalt parking lots on hot summer days or building rooftops.
• Hazy skies, fog, and mist can also make it difficult to focus when viewing terrestrially. The amount of detail seen under these conditions is greatly reduced.
• If you wear corrective lenses (specifically glasses), you may want to remove them when observing with an eyepiece attached to the telescope. When using a camera, however, you should always wear corrective lenses to ensure the sharpest possible focus. If you have astigmatism, corrective lenses must be worn at all times.

Astronomy Basics

To understand your telescope more thoroughly, you need to know a little about the night sky. This section deals with observational astronomy in general and includes information on the night sky and polar alignment.

For telescopes with equatorial mounts, users have setting circles and polar alignment methods to find objects. With your altazimuth mount, you can use a method called "star hopping," described in the "Celestial Observing Section." Good star maps are essential for locating deep sky objects, and current monthly astronomy magazines help locate planets.

The Celestial Coordinate System

To help find objects in the sky, astronomers use a celestial coordinate system similar to our geographical co-ordinate system. The celestial coordinate system has poles, lines of longitude and latitude, and an equator. For the most part, these remain fixed against the background stars.

The celestial equator runs 360 degrees around the Earth and separates the northern celestial hemisphere from the southern. Like Earth's equator, it reads zero degrees. On Earth, this is latitude; in the sky, it is declination (DEC). Lines of declination are named for their angular distance above and below the celestial equator, broken down into degrees, minutes of arc, and seconds of arc. Declination readings south of the equator carry a minus sign (-), and those north are either blank or preceded by a plus sign (+).

Figure 4-1: The celestial sphere seen from the outside showing R.A. and DEC.

The celestial equivalent of longitude is called Right Ascension (R.A.). Like Earth's lines of longitude, they run from pole to pole and are evenly spaced 15 degrees apart. Although separated by angular distance, longitude lines also measure time; each line is one hour apart. Since Earth rotates once every 24 hours, there are 24 lines. R.A. coordinates are marked in units of time, beginning with an arbitrary point in Pisces designated as 0 hours, 0 minutes, 0 seconds. Other points are designated by how far they lag behind this coordinate after it passes overhead moving west.

Motion of the Stars

The daily motion of the Sun across the sky is familiar to most observers. This daily trek is not the Sun moving, but the result of Earth's rotation. Earth's rotation also causes stars to move, scribing a large circle as Earth completes one rotation. The size of the circular path a star follows depends on its position in the sky. Stars near the celestial equator form the largest circles, rising in the east and setting in the west. Moving toward the north celestial pole, the point around which stars in the northern hemisphere appear to rotate, these circles become smaller. Stars at mid-celestial latitudes rise in the northeast and set in the northwest. Stars at high celestial latitudes are always above the horizon and are said to be circumpolar because they never rise and never set.

You will never see stars complete a full circle because sunlight during the day washes out starlight. However, part of this circular motion can be seen by setting up a camera on a tripod and opening the shutter for a couple of hours. The timed exposure will reveal semicircles that revolve around the pole. This description of stellar motions also applies to the southern hemisphere, where stars south of the celestial equator move around the south celestial pole.

Figure 4-2: Illustrates star paths: stars seen near the north celestial pole, stars seen near the celestial equator, and stars seen looking in the opposite direction of the north celestial pole. All stars appear to rotate around the celestial poles, but the appearance varies. Near the north celestial pole, stars scribe recognizable circles (1). Near the celestial equator, paths are interrupted by the horizon, appearing to rise and set (2). Looking toward the opposite pole, stars curve or arc in the opposite direction (3).

Celestial Observing

With your telescope set up, you are ready to use it for observing. This section covers visual observing hints for both solar system and deep sky objects, as well as general observing conditions.

Observing the Moon

Often, it is tempting to look at the Moon when it is full. At this time, the face we see is fully illuminated and its light can be overpowering. Little or no contrast can be seen during this phase.

One of the best times to observe the Moon is during its partial phases (around the time of first or third quarter). Long shadows reveal a great amount of detail on the lunar surface. At low power, you will be able to see most of the lunar disk at one time. Change to optional eyepieces for higher power (magnification) to focus in on a smaller area.

Lunar Observing Hints: To increase contrast and bring out detail on the lunar surface, use optional filters. A yellow filter works well at improving contrast, while a neutral density or polarizing filter will reduce overall surface brightness and glare.

Observing the Planets

Other fascinating targets include the five naked eye planets. You can see Venus go through its lunar-like phases. Mars can reveal a host of surface detail and one, if not both, of its polar caps. You will be able to see the cloud belts of Jupiter and the great Red Spot (if visible). You can also see the moons of Jupiter as they orbit the giant planet. Saturn, with its beautiful rings, is easily visible at moderate power.

Planetary Observing Hints:

• Remember that atmospheric conditions are usually the limiting factor on how much planetary detail will be visible. Avoid observing planets when they are low on the horizon or directly over a source of radiating heat, such as a rooftop or chimney. See the "Seeing Conditions" section.
• To increase contrast and bring out detail on the planetary surface, try using Celestron eyepiece filters.

Observing the Sun

Although overlooked by many amateur astronomers, solar observation is both rewarding and fun. However, because the Sun is so bright, special precautions must be taken to avoid damaging your eyes or your telescope.

For safe solar viewing, use a solar filter that reduces the intensity of the Sun's light. With a filter, you can see sunspots as they move across the solar disk and faculae, which are bright patches seen near the Sun's edge.

• The best time to observe the Sun is in the early morning or late afternoon when the air is cooler.
• To center the Sun without looking into the eyepiece, watch the shadow of the telescope tube until it forms a circular shadow.

Observing Deep Sky Objects

Deep-sky objects are those objects outside the boundaries of our solar system, including star clusters, planetary nebulae, diffuse nebulae, double stars, and galaxies outside our Milky Way. Most deep-sky objects have a large angular size, so low-to-moderate power is sufficient. Visually, they are too faint to reveal the color seen in long exposure photographs; instead, they appear black and white. Because of their low surface brightness, they should be observed from a dark-sky location. Light pollution around large urban areas washes out most nebulae, making them difficult to observe. Light Pollution Reduction filters help reduce background sky brightness, thus increasing contrast.

Star Hopping

One convenient way to find deep-sky objects is by star hopping, using bright stars to "guide" you to an object. For successful star hopping, it is helpful to know your telescope's field of view. If using the standard 20mm eyepiece with the AstroMaster LT telescope, your field of view is approximately 1°. If an object is 3° away, you need to move 3 fields of view. Consult the "Determining Field of View" section for other eyepieces.

The Andromeda Galaxy (M31) is an easy target. To find M31:

1. Locate the constellation of Pegasus, a large square visible in the fall (eastern sky, moving toward overhead) and winter months (overhead, moving toward the west).
2. Start at the star in the northeast corner – Alpha (α) Andromedae.
3. Move northeast approximately 7°. There you will find two stars of equal brightness – Delta (δ) and Pi (π) Andromeda – about 3° apart.
4. Continue in the same direction another 8°. There you will find two stars – Beta (β) and Mu (μ) Andromedae – also about 3° apart.
5. Move 3° northwest – the same distance between the two stars – to the Andromeda galaxy.

Figure 5-1: Star chart showing constellations like Andromeda, Cassiopeia, and Triangulum, with labels for stars and deep sky objects like M31 (Andromeda Galaxy).

Star hopping to the Andromeda Galaxy (M31) is simple, as all the stars needed are visible to the naked eye.

Star hopping takes practice, and objects without nearby naked-eye stars are challenging. One such object is M57, the Ring Nebula. Here's how to find it:

1. Find the constellation of Lyra, a small parallelogram visible in the summer and fall months. Lyra is easy to pick out because it contains the bright star Vega.
2. Start at the star Vega – Alpha (α) Lyrae – and move a few degrees southeast to find the parallelogram. The four stars forming this geometric shape are similar in brightness.
3. Locate the two southernmost stars of the parallelogram – Beta (β) and Gamma (γ) Lyra.
4. Point about halfway between these two stars.
5. Move about ½° toward Beta (β) Lyra, while remaining on a line connecting the two stars.
6. Look through the telescope; the Ring Nebula should be in your field of view. The Ring Nebula's angular size is quite small and difficult to see.
7. Because the Ring Nebula is rather faint, you may need to use "averted vision." "Averted vision" is a technique of looking slightly away from the object. Center the Ring Nebula in your field of view and then look off to the side. This causes light from the object to fall on the black and white sensitive rods of your eyes, rather than the color-sensitive cones. (Remember that when observing faint objects, it's important to observe from a dark location, away from street and city lights. The average eye takes about 20 minutes to fully adapt to darkness. Use a red-filtered flashlight to preserve your dark-adapted night vision).

These examples should give you an idea of how to star hop to deep-sky objects. To use this method on other objects, consult a star atlas, then star hop to the object of your choice using "naked eye" stars.

Figure 5-2: Star chart showing the constellation Lyra, with labels for Vega, M57 (The Ring Nebula), and other stars.

Seeing Conditions

Viewing conditions affect what you can see through your telescope during an observing session. Conditions include transparency, sky illumination, and seeing. Understanding viewing conditions and their effect will help you get the most out of your telescope.

Transparency

Transparency is the clarity of the atmosphere, affected by clouds, moisture, and other airborne particles. Thick cumulus clouds are opaque, while cirrus can be thin, allowing light from the brightest stars through. Hazy skies absorb more light than clear skies, making fainter objects harder to see and reducing contrast on brighter objects. Aerosols from volcanic eruptions also affect transparency. Ideal conditions are when the night sky is inky black.

Sky Illumination

General sky brightening caused by the Moon, aurorae, natural airglow, and light pollution greatly affects transparency. While not a problem for brighter stars and planets, bright skies reduce the contrast of extended nebulae, making them difficult to see. To maximize your observing, limit deep sky viewing to moonless nights far from light-polluted urban areas. LPR filters enhance deep sky viewing from light-polluted areas by blocking unwanted light while transmitting light from certain deep sky objects. You can observe planets and stars from light-polluted areas or when the Moon is out.

Seeing

Seeing conditions refer to the stability of the atmosphere and directly affect the amount of fine detail seen in extended objects. The air in our atmosphere acts as a lens, bending and distorting incoming light rays. The amount of bending depends on air density. Varying temperature layers have different densities and therefore bend light differently. Light rays from the same object arrive slightly displaced, creating an imperfect or smeared image. These atmospheric disturbances vary from time-to-time and place-to-place. The size of the air parcels compared to your aperture determines the "seeing" quality. Under good seeing conditions, fine detail is visible on brighter planets like Jupiter and Mars, and stars are pinpoint images. Under poor seeing conditions, images are blurred and stars appear as blobs.

The conditions described here apply to both visual and photographic observations.

Figure 5-3: Drawings representing a point source (star) under bad seeing conditions (left) to excellent conditions (right). Most often, seeing conditions produce images somewhere between these two extremes.

Astrophotography

The AstroMaster LT series of telescopes was designed for visual observing. After looking at the night sky for a while, you may want to try your hand at photography. Several forms of photography are possible for celestial and terrestrial pursuits. Below is a brief discussion of some methods, with suggestions to search out books for detailed information.

As a minimum, you will need a digital camera or a 35mm SLR camera. Attach your camera to the telescope with:

• Digital camera: You will need the Universal Digital Camera Adapter (# 93626). The adapter allows the camera to be mounted rigidly for terrestrial as well as prime focus astrophotography.
• 35mm SLR camera: You will need to remove your lens from the camera and attach a T-Ring for your specific camera brand. Then, you will need a T-Adapter (# 93625) to attach to the T-Ring and the telescope focuser tube. Your telescope then acts as the camera lens.

Short Exposure Prime Focus Photography

Short exposure prime focus photography is the best way to begin imaging celestial objects. It is done by attaching your camera to the telescope as described above. Keep these points in mind:

• Polar align the telescope and start the optional motor drive for tracking.
• You can image the Moon as well as brighter planets. Experiment with various settings and exposure times. Much information can be obtained from your camera instruction manual, which can supplement detailed books on the subject.
• Do your photography from a dark sky observing site if possible.

Planetary & Lunar Photography with Special Imagers

In recent years, new technology has evolved that makes taking superb images of the planets and moon relatively easy, with amazing results. Celestron offers the NexImage (# 93712), a special camera with included image processing software. You can capture planetary images on your first night out that rival what professionals were doing with large telescopes just a few years ago.

CCD Imaging for Deep Sky Objects

Special cameras have been developed for taking images of deep sky objects. These have evolved over the last several years to become more economical, allowing amateurs to take fantastic images. Several books have been written on how to get the best images possible. The technology continues to evolve with better and easier-to-use products.

Terrestrial Photography

Your telescope makes an excellent telephoto lens for terrestrial (land) photography. You can take images of various scenic views, wildlife, nature, and just about anything. Experiment with focusing, speeds, etc., to get the best image desired. You can adapt your camera per the instructions at the top of this page.

Telescope Maintenance

While your telescope requires little maintenance, there are a few things to remember to ensure your telescope performs at its best.

Care and Cleaning of the Optics

Occasionally, dust and/or moisture may build up on the objective lens or primary mirror, depending on the telescope type. Special care should be taken when cleaning any instrument so as not to damage the optics.

If dust has built up on the optics, remove it with a brush (made of camel's hair) or a can of pressurized air. Spray at an angle to the glass surface for approximately two to four seconds. Then, use an optical cleaning solution and white tissue paper to remove any remaining debris. Apply the solution to the tissue and then apply the tissue paper to the optics. Low pressure strokes should go from the center of the lens (or mirror) to the outer portion. Do NOT rub in circles!

You can use a commercially made lens cleaner or mix your own. A good cleaning solution is isopropyl alcohol mixed with distilled water (60% isopropyl alcohol and 40% distilled water). Alternatively, liquid dish soap diluted with water (a couple of drops per one quart of water) can be used.

Occasionally, you may experience dew build-up on the optics during an observing session. If you want to continue observing, the dew must be removed, either with a hair dryer (on low setting) or by pointing the telescope at the ground until the dew has evaporated.

If moisture condenses on the inside of the optics, remove the accessories from the telescope. Place the telescope in a dust-free environment and point it down. This will remove the moisture from the telescope tube.

To minimize the need to clean your telescope, replace all lens covers once you have finished using it. Since the cells are NOT sealed, the covers should be placed over the openings when not in use. This will prevent contaminants from entering the optical tube.

Internal adjustments and cleaning should be done only by the Celestron repair department. If your telescope is in need of internal cleaning, please call the factory for a return authorization number and price quote.

Collimation of a Newtonian

The optical performance of most Newtonian reflecting telescopes can be optimized by re-collimating (aligning) the telescope's optics as needed. To collimate the telescope simply means to bring its optical elements into balance. Poor collimation will result in optical aberrations and distortions.

Before collimating your telescope, familiarize yourself with all its components. The primary mirror is the large mirror at the back end of the telescope tube. This mirror is adjusted by loosening and tightening the three screws, placed 120 degrees apart, at the end of the telescope tube. The secondary mirror (the small, elliptical mirror under the focuser, in the front of the tube) also has three adjustment screws. To determine if your telescope needs collimation, first point your telescope toward a bright wall or blue sky outside.

Aligning the Secondary Mirror

The following describes the procedure for daytime collimation using the optional Newtonian Collimation Tool (#94183) or the optional Collimation Eyepiece 1 ¼" (# 94182).

If you have an eyepiece in the focuser, remove it. Rack the focuser tube in completely, using the focusing knobs, until its silver tube is no longer visible. You will be looking through the focuser at a reflection of the secondary mirror, projected from the primary mirror. During this step, ignore the silhouetted reflection from the primary mirror. Insert the collimating cap into the focuser and look through it. With the focus pulled in all the way, you should be able to see the entire primary mirror reflected in the secondary mirror. If the primary mirror is not centered in the secondary mirror, adjust the secondary mirror screws by alternately tightening and loosening them until the periphery of the primary mirror is centered in your view. DO NOT loosen or tighten the center screw in the secondary mirror support, as it maintains proper mirror position.

Aligning the Primary Mirror

Now adjust the primary mirror screws to re-center the reflection of the small secondary mirror, so it's silhouetted against the view of the primary. As you look into the focuser, silhouettes of the mirrors should look concentric. Repeat steps one and two until this is achieved.

Remove the collimating cap and look into the focuser, where you should see the reflection of your eye in the secondary mirror.

Diagrams showing Newtonian collimation views through the focuser using a collimation cap: Secondary mirror needs adjustment, Primary mirror needs adjustment, Both mirrors aligned with the collimating cap in the focuser, Both mirrors aligned with your eye looking into the focuser.

Night Time Star Collimating

After successfully completing daytime collimation, night time star collimation can be done by closely adjusting the primary mirror while the telescope tube is on its mount and pointing at a bright star. The telescope should be set up at night, and a star's image should be studied at medium to high power (30-60 power per inch of aperture). If a non-symmetrical focus pattern is present, it may be possible to correct this by re-collimating only the primary mirror.

Procedure:

To star collimate in the Northern Hemisphere, point at a stationary star like the North Star (Polaris). It can be found in the north sky, at a distance above the horizon equal to your latitude. It's also the end star in the handle of the Little Dipper. Polaris is not the brightest star in the sky and may appear dim, depending upon your sky conditions.

Prior to re-collimating the primary mirror, locate the collimation screws on the rear of the telescope tube. The rear cell has three large thumbscrews for collimation and three small thumbscrews to lock the mirror in place. The collimation screws tilt the primary mirror. Start by loosening the small locking screws a few turns each. Normally, motions of about 1/8 turn will make a difference, with approximately 1/2 to 3/4 turn being the maximum required for the large collimation screws. Turn one collimation screw at a time and use a collimation tool or eyepiece to see how collimation is affected. It will take some experimenting, but you will eventually get the centering you desire.

It is best to use the optional collimation tool or collimating eyepiece. Look into the focuser and notice if the secondary reflection has moved closer to the center of the primary mirror.

With Polaris or a bright star centered within the field of view, focus with either the standard ocular or your highest power ocular (shortest focal length in mm, such as 6mm or 4mm). Another option is to use a longer focal length ocular with a Barlow lens. When a star is in focus, it should look like a sharp pinpoint of light. If, when focusing on the star, it is irregular in shape or appears to have a flare of light at its edge, your mirrors aren't in alignment. If you notice the appearance of a flare of light from the star that remains stable in location, just as you go in and out of exact focus, then re-collimation will help sharpen the image.

Diagrams showing star patterns under different focus conditions, indicating asymmetry and skew due to poor collimation.

When satisfied with the collimation, tighten the small locking screws. Note the direction the light appears to flare. For example, if it flares toward the three o'clock position, move whichever screw or combination of collimation screws necessary to move the star's image toward the direction of the flaring. It may only be necessary to adjust a screw enough to move the star's image from the center of the field of view to about halfway, or less, toward the field's edge (when using a high power ocular).

Collimation adjustments are best made while viewing the star's position and turning the adjustment screws simultaneously. This way, you can see exactly which way the movement occurs. It may be helpful to have two people working together: one viewing and instructing, and the other performing the adjustments.

IMPORTANT: After making the first, or each adjustment, it is necessary to re-aim the telescope tube to re-center the star in the field of view. The star image can then be judged for symmetry by going just inside and outside of exact focus and noting the star's pattern. Improvement should be seen if proper adjustments are made. Since three screws are present, it may be necessary to move at least two to achieve the necessary mirror movement.

Diagram showing a collimated telescope appearing as a symmetrical ring pattern similar to a diffraction disk.

AstroMaster LT Specifications

Note: Specifications are subject to change without notice or obligation.

Note: This equipment has been tested and found to comply with the limits for a Class B digital device, pursuant to part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference in a residential installation. This equipment generates, uses and can radiate radio frequency energy and, if not installed and used in accordance with the instructions, may cause harmful interference to radio communications. However, there is no guarantee that interference will not occur in a particular installation. If this equipment does cause harmful interference to radio or television reception, which can be determined by turning the equipment off and on, the user is encouraged to try to correct the interference by one or more of the following measures:

• Reorient or relocate the receiving antenna.
• Increase the separation between the equipment and receiver.
• Connect the equipment into an outlet on a circuit different from that to which the receiver is connected.
• Consult the dealer or an experienced radio/TV technician for help.

Celestron
2835 Columbia Street
Torrance, CA 90503 U.S.A.
Tel. (310) 328-9560
Fax. (310) 212-5835
Website www.celestron.com

Copyright 2012 Celestron
All rights reserved.

(Products or instructions may change without notice or obligation.)

Designed and intended for those 13 years of age and older

WARNING: This product contains a chemical(s) known to the State of California to cause cancer, birth defects or other reproductive harm.

Item # 21061-INST
Printed in China
$10.00
06-07

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