Celestron AstroMaster Series Telescopes

Introduction

Congratulations on your purchase of an AstroMaster series telescope! The AstroMaster series offers several models, and this guide covers three different models mounted on an Alt-AZ mount (the altazimuth mount is the simplest type with two movements – altitude (up and down) and azimuth (sideways movement) – a 70mm refractor, a 90mm refractor, and a 114mm Newtonian. The AstroMaster series is manufactured with superior quality materials ensuring stability and durability. All these elements combined make these telescopes instruments capable of providing a lifetime of satisfaction with minimal maintenance.

The very design of these instruments is such that a first-time telescope buyer benefits from an exceptional product. The AstroMaster series stands out with its compact and portable design, as well as significant optical performance intended to encourage any newcomer to the world of amateur astronomy. Furthermore, your AstroMaster telescope is perfectly suited for terrestrial observations thanks to its high and impressive magnification power.

AstroMaster telescopes come with a two-year limited warranty. For more information, visit our website at www.celestron.com.

Here are some of the many features of the AstroMaster:

• All optical elements are made of coated glass to provide clear and sharp images.
• Rigid altazimuth mount that maneuvers easily with a large, integrated lever for easy targeting.
• Pre-assembled steel tripod with 31 mm (1.25 in) legs offering a stable platform.
• Quick and simple tool-free setup.
• “The Sky” Level 1 CD-ROM – astronomy software offering sky information with printable sky charts.
• All models can be used terrestrially or astronomically with the standard accessories supplied.

Take the time to read this guide before you begin exploring the universe. As you will likely need several observation sessions to familiarize yourself with your telescope, keep this guide handy until you have mastered its operation. The guide provides detailed information on each step, as well as reference documentation and practical tips that will make your observations as simple and enjoyable as possible.

Your telescope has been designed to provide you with years of pleasure and enriching observations. However, before you start using it, you must consider certain safety precautions to ensure your safety and protect your equipment.

Warnings

• Never look directly at the Sun with the naked eye or through a telescope (unless equipped with a suitable solar filter). Permanent and irreversible eye damage could occur.
• Never use your telescope to project an image of the Sun onto any surface. Heat buildup inside can damage the telescope and any accessories attached to it.
• Never use an eyepiece solar filter or a Herschel wedge. Due to heat buildup inside the telescope, these devices can crack or break, allowing unfiltered sunlight to reach your eyes.
• Never leave the telescope unattended with children or adults who are not familiar with its normal operating procedures.

Assembly

Telescope Diagrams

Figure 1-1: AstroMaster 90AZ Astronomical Refractor (Similar to the AstroMaster 70AZ Refractor)

• 1. Objective
• 2. Telescope optical tube
• 3. Star Pointer finder
• 4. Eyepiece
• 5. 90° Diagonal
• 6. Focus knob
• 7. Handle
• 8. Accessory tray
• 9. Tripod
• 10. Azimuth lock knob
• 11. Alt-Az mount
• 12. Dovetail plate

Figure 1-2: AstroMaster 114 AZ Newtonian

• 1. Star Pointer finder
• 2. Eyepiece
• 3. Telescope tube ring
• 4. Telescope optical tube
• 5. Primary mirror
• 6. Handle
• 7. Azimuth lock knob
• 8. Accessory tray
• 9. Tripod
• 10. Alt-Az mount
• 11. Dovetail plate
• 12. Focus knob

Tripod Installation

This chapter explains how to assemble your AstroMaster telescope. Your telescope should be assembled indoors the first time to easily identify the different parts and familiarize yourself with the correct assembly procedure before attempting to do so outdoors.

Each AstroMaster comes in a carton. The carton contains the following parts: optical tube with Star Pointer finder and tube rings attached (114 AZ only), Alt-Az mount with handle attached, 10mm 1.25in eyepiece, 20mm 1.25in eyepiece (image corrector for the 114AZ), 90° diagonal image corrector 1.25in (for 70AZ and 90 AZ), “The Sky” Level 1 CD-ROM.

1. Remove the tripod from the carton (Figure 2-1). The tripod comes pre-assembled to facilitate installation.
2. Set the tripod upright and extend each leg until fully extended, then lightly press on the tripod's central support (Figure 2-2). The upper part of the tripod is called the tripod head.
3. Next, install the tripod accessory tray (Figure 2-3) onto the tripod's central support (center of Figure 2-2).
4. Insert the cutout in the middle of the tray (flat side of the tray facing down) to center it on the tripod's central support and push it down slightly (Figure 2-4). The tray's tabs should be positioned as shown in Figure 2-4.
5. Rotate the tray until the tabs are positioned under the support for each leg and press lightly until they click into place (Figure 2-5). The tripod is now assembled (Figure 2-6).
6. You can adjust the tripod's telescopic legs to your desired height. The lowest height is 61 cm (24 in) and the highest is 104 cm (41 in). Unlock the locking knob on each tripod leg (Figure 2-7) and extend the legs to the desired height, then firmly retighten the knob. Figure 2-8 shows an illustration of a fully extended tripod.
7. The tripod will offer greater rigidity and stability at its lowest height setting.

Manual Telescope Movement

The AstroMaster's Alt-AZ mount moves easily in the direction you want to point it. Up-and-down rotation (altitude) is controlled by the handle (Figure 2-10). Sideways rotation (azimuth) is controlled by the azimuth lock knob (Figure 2-9). Both the handle and the azimuth locking device are loosened by turning them counter-clockwise. Loosen these controls to find objects more easily, then retighten them. To lock the controls in position, turn them clockwise.

Attaching the Telescope Tube to the Mount

The telescope's optical tube attaches to the mount via a dovetail plate with a guide slot at the top of the mount (Figure 2-11). For the 114 AZ Newtonian, the plate is attached to the tube rings. For the 70AZ and 90AZ refractors, the plate is attached to the underside of the telescope tube. Before attaching the optical tube, ensure that the handle and azimuth lock knob are securely locked. Then, position the dovetail plate horizontally as shown in Figure 2-10. This will prevent the mount from moving abruptly during the attachment of the telescope's optical tube. Also, remove the objective cap (refractor) or the front opening cap (Newtonian). To attach the telescope tube:

1. Remove the protective paper covering the optical tube. For the 114EQ Newtonian, you will need to remove the tube rings to remove the paper.
2. Loosen the mounting knob and the safety screw on the side of the dovetail plate's platform so they do not protrude onto the mounting plate – see Figure 2-18.
3. Slide the dovetail plate into the recess at the top of the mounting plate (Figure 2-17).
4. Tighten the mounting knob on the dovetail plate's platform to secure the telescope in position.
5. Manually tighten the safety screw on the plate's platform until its tip touches the side of the plate.

REMARK: Never loosen any of the telescope tube or mount knobs other than the right ascension and declination knobs.

Installing the 90° Diagonal and Eyepieces (Refractor)

The 90° diagonal is a prism that deflects light perpendicularly to the light's path from the refractor. This allows for a more comfortable viewing position than looking directly into the tube. This 90° diagonal is an image corrector that rights the image, making it upright and correctly oriented from left to right, which is advantageous for terrestrial observations. Additionally, the 90° diagonal can be rotated to the position that best suits you. To install the 90° diagonal and eyepieces:

1. Insert the small barrel of the 90° diagonal into the 1.25 in eyepiece adapter on the refractor's focuser – Figure 2-13. Ensure that the two thumbscrews on the eyepiece adapter do not protrude into the focuser tube before installation and that the cap has been removed from the eyepiece adapter.
2. Insert the chrome barrel end of one of the eyepieces into the 90° diagonal and tighten the thumbscrew. Again, ensure the thumbscrew does not protrude into the 90° diagonal before inserting the eyepiece.
3. Eyepiece focal lengths can be changed by reversing the procedure described above in step 2.

Installing Eyepieces on Newtonians

The eyepiece is the optical element that magnifies the image focused by the telescope. Without an eyepiece, it would be impossible to use the telescope visually. Eyepieces are often designated by their focal length and barrel diameter. Focal length is inversely proportional to eyepiece power: the longer the focal length (i.e., the higher the number), the lower the eyepiece magnification (i.e., the power). Generally, you will use low to moderate magnification power for your observation sessions. For more information on how to adjust magnification, consult the chapter titled “Magnification Calculation.” The eyepiece fits directly onto the focuser of Newtonians. To attach eyepieces:

1. Ensure the thumbscrews do not protrude into the focuser tube. Then, insert the eyepiece's chrome barrel into the focuser tube (remove the focuser cap first) and tighten the thumbscrews – see Figure 2-14.
2. The 20mm eyepiece is called an image-erecting eyepiece because it corrects the image to be upright and correctly oriented from left to right. This feature allows the telescope to be used for terrestrial observations.
3. Eyepieces can be changed by reversing the procedure described above.

Fundamentals of Telescopes

A telescope is an instrument that collects and focuses light. The way light is focused is determined by the type of optical design. Some telescopes, known as refractors, use lenses, while reflector telescopes (Newtonians) are equipped with mirrors.

Developed in the early 17th century, the refractor is the oldest type of telescope. Its name comes from the method it uses to converge incident light rays. The refractor uses a lens to bend or reflect incident light rays, hence its name (see Figure 3-1). Early models consisted of single-element lenses. However, the single lens has the drawback of acting like a prism, splitting light into different colors of the rainbow, a phenomenon known as chromatic aberration. To overcome this problem, a two-element lens, known as an achromat, was introduced. Each element has a different refractive index, allowing two different wavelengths of light to converge at the same point. Most two-element lenses, typically made of crown and flint glasses, are corrected for red and green light. Blue light can be converged at a slightly different point.

A Newtonian reflector uses a single concave mirror as its primary mirror. Light enters the tube to reach the mirror at the end. The mirror's curvature then reflects the light back towards the front of the tube to a single point, the focal point. Since you cannot place your head in front of the telescope to view an image with an eyepiece, a flat mirror called a 90° diagonal intercepts the light and reflects it to the side of the tube, perpendicular to it. The eyepiece is placed there to facilitate observation.

Newtonian reflector telescopes replace heavy lenses with mirrors to collect and converge light, offering greater light-gathering power for the price. Since the light path is intercepted and reflected to the side, focal lengths of up to 1000 mm are possible with a relatively compact and portable telescope. A Newtonian reflector telescope offers such impressive light-gathering capabilities that even with a modest budget, you can seriously explore distant objects in astronomy. Newtonian reflector telescopes require a bit more care and maintenance as the primary mirror is exposed to air and dust. However, this minor inconvenience does not diminish the popularity of this type of telescope for those who want an economical telescope capable of resolving faint and distant objects.

Figure 3-1: Cross-section view of light path in a refractor optical design

Figure 3-2: Cross-section view of light path in a Newtonian optical design

Image Orientation

Image orientation depends on how the eyepiece is inserted into the telescope. If you observe with a 90° diagonal using refractors, the image will be upright but left-right reversed (mirror image effect). If you insert the eyepiece directly into the refractor's focuser (i.e., without the 90° diagonal), the image is inverted and left-right reversed. However, using the AstroMaster refractor with the standard image-erecting 90° diagonal provides correct image orientation.

Newtonian reflectors produce an upright image, but it will appear rotated depending on the position of the eyepiece holder relative to the ground. However, using the image-erecting eyepiece supplied with the AstroMaster Newtonians will provide good image orientation.

Figure 3-3: Image orientation as seen with the naked eye and using image correctors on refractors and Newtonians

Figure 3-3: Left-right reversed image as seen with a 90° diagonal on a refractor

Figure 3-3: Normal reversed image with Newtonians and as seen with the eyepiece directly in a refractor

Focusing

To focus your refractor or Newtonian telescope, simply turn the focus knob located directly below the eyepiece holder (see Figures 1-1 and 1-2). Turn this knob clockwise to focus on an object farther away than what you are currently observing. Turn the knob counter-clockwise to focus on an object closer than what you are currently observing.

Remark: If you wear corrective lenses (especially eyeglasses), it may be helpful to remove them before observing with an eyepiece attached to the telescope. However, when using a camera, you should always wear your corrective lenses to achieve the most precise focus. If you have astigmatism, you must wear your corrective lenses permanently.

Aligning the Finder

The Star Pointer is the quickest and easiest way to accurately point the telescope at a desired object in the sky. It's like having a laser pointer that you can direct straight at the night sky. The Star Pointer is a zero-magnification aiming device with a coated glass window that allows you to superimpose the image of a small red dot onto the night sky. When looking through the finder, keep both eyes open and simply point your telescope so that the red dot observed in the Star Pointer aligns with the object seen with the naked eye. The red dot is produced by a light-emitting diode (LED); it is not a laser beam and poses no danger to the glass window or your eyes. The Star Pointer is powered by a long-lasting 3-volt lithium battery (ref. CR 1620), see Figure 3-4. As with all types of finders, it must be correctly aligned with the main telescope before it can be used. Alignment is best done at night, as the red LED is harder to see during the day.

Calculating Magnification

You can change your telescope's power by simply changing the eyepiece. To determine your telescope's magnification, divide the telescope's focal length by the focal length of the eyepiece used. The equation is as follows:

Magnification = Distance focale du télescope (mm) / Distance focale de l'oculaire (mm)

For example, suppose you are using the 20mm eyepiece supplied with your telescope. To determine the magnification, simply divide the telescope's focal length (e.g., the AstroMaster 70AZ has a focal length of 900mm) by the eyepiece's focal length, which is 20mm. 900 divided by 20 equals a magnification of 45.

Although the power is adjustable, all observation instruments are limited to a maximum useful magnification for an ordinary sky. As a general rule, use a magnification of 60 for each inch (25.4 mm) of aperture. For example, the AstroMaster 70AZ has a diameter of 71mm (2.8 inches). Multiplying 2.8 by 60 gives a maximum useful magnification of 168. While this is the maximum useful magnification, most observations are made within a magnification range of 20 to 35 per 25.4mm of aperture, which is a magnification range of 56 to 98 for the AstroMaster 70AZ telescope. You can determine your telescope's magnification in the same way.

Establishing Field of View (FOV)

Establishing the field of view is important if you want to get an idea of the apparent diameter of the observed object. To calculate the actual field of view, divide the eyepiece's apparent field of view (provided by the eyepiece manufacturer) by the magnification. The equation is as follows:

Actual Field of View = Apparent Field of View of Eyepiece / Magnification

As you can see, it is necessary to calculate the magnification before establishing the field of view. Using the example above, we can determine the field of view with the same 20mm eyepiece supplied with all AstroMaster 70AZ telescopes. The apparent field of view of a 20mm eyepiece is 50°. Dividing 50° by the magnification of 45 gives a field of view of 1.1°.

To convert degrees to feet at 1000 yards, which is more useful for terrestrial observations, simply multiply by 52.5. In our example, multiply the angular field of 1.1° by 52.5. The linear field width is then 17.6 meters (58 feet) at a distance of one thousand yards (914.4 meters).

General Observation Tips

Using an optical instrument requires knowledge of certain elements to achieve the best possible image quality.

• Never look through glass. Household window panes have optical defects, and their thickness varies from one point to another. These irregularities can affect your telescope's focusing capability. In most cases, you will not be able to achieve a perfectly sharp image and may even experience double vision.
• Never look beyond or over objects that produce heat waves, such as asphalt parking lots on hot summer days, or building rooftops.
• Hazy skies, fog, and mist can create focusing difficulties for terrestrial observation. Details are much less visible under these conditions.
• If you wear corrective lenses (especially eyeglasses), it may be helpful to remove them before observing with an eyepiece attached to the telescope. However, when using a camera, you should always wear your corrective lenses for the most precise focus. If you have astigmatism, you must wear your corrective lenses permanently.

Fundamentals of Astronomy

Up to this point, this guide has covered the assembly and basic operation of your telescope. However, to better understand this instrument, you need to familiarize yourself with the night sky. This chapter covers observational astronomy in general and includes information on the night sky and polar alignment. For telescopes equipped with equatorial mounts, users have methods for setting circles and polar alignment that make it easier to find objects in the sky. With the altazimuth mount, you can use the "star hopping" (visual tracking) method described later in this manual, in the "Celestial Observation" chapter. Good star charts are essential to help you locate deep-sky objects, and various astronomy magazines and periodicals will help you locate planets.

The Celestial Coordinate System

To find celestial objects, astronomers use a celestial coordinate system similar to the geographic coordinate system used on Earth. The celestial coordinate system has poles, lines of longitude and latitude, and an equator. Overall, these reference points remain fixed relative to the stars.

The celestial equator circles the Earth 360 degrees and separates the northern celestial hemisphere from the southern celestial hemisphere. Like the Earth's equator, it has an initial position of zero degrees. On Earth, this corresponds to latitude. However, in the sky, it is referred to as declination, or DEC for short. Declination lines are named based on their angular distance above and below the celestial equator. These lines are divided into degrees, minutes of arc, and seconds of arc. Declination figures south of the equator are preceded by a minus sign (-) before the coordinates, and those of the northern celestial equator are either blank (i.e., no designation) or preceded by a plus sign (+).

The celestial equivalent of longitude is called right ascension, or RA for short. Like terrestrial longitude lines, these lines run from pole to pole and are spaced regularly every 15 degrees. Although longitude lines are separated by an angular distance, they are also a measure of time. Each longitude line is placed one hour apart from the next. Since the Earth completes one revolution in 24 hours, there are a total of 24 lines. For this reason, right ascension coordinates are expressed in time units. The starting point is an arbitrary point in the constellation Pisces, located at 0 hours, 0 minutes, 0 seconds. All other points are designated by the distance (i.e., the time) that separates them from this coordinate once they have passed it following its celestial path westward.

Figure 4-1: The celestial sphere viewed from the outside with right ascension and declination.

Star Movement

The daily movement of the Sun across the sky is familiar even to a novice observer. This daily progression is not due to the Sun's movement, as early astronomers believed, but to the Earth's rotation. The Earth's rotation causes the stars to do the same, describing a large circle as the Earth completes a revolution. The size of a star's circular path 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. As you move towards the celestial north pole, the point around which the stars of 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 called circumpolar because they never rise or set. You will never see stars complete a circle because sunlight during the day dims their brightness. However, it is possible to partially observe this circular movement of stars in this region by setting a camera on a tripod and opening the shutter for about two hours. The timed exposure will reveal semicircles rotating around the pole. (This description of stellar movements also applies to the southern hemisphere, with the difference that all stars south of the celestial equator move around the celestial south pole).

Figure 4-2: All stars appear to rotate around the celestial poles. However, the aspect of this movement varies depending on where you look in the sky. Near the celestial north pole, stars describe recognizable circles centered on the pole (1). Stars near the celestial equator also follow circular paths around the pole. Nevertheless, the path is interrupted by the horizon. They therefore appear to rise in the east and set in the west (2). If you look towards the opposite pole, the star's curve or the arc of the opposite direction describes a circle around the opposite pole (3).

Celestial Observation

Once your telescope is set up, you can begin your observation sessions. This chapter covers tips for visual observation of solar system and deep-sky objects, as well as general observation conditions that affect your observation capabilities.

Observing the Moon

It is often tempting to look at the Moon when it is full. This is when the visible face is fully illuminated and the brightness can be too intense. Furthermore, there is little or no contrast during this phase.

Partial phases of the Moon are among the most rewarding moments for lunar observation (around the first or third quarter). Elongated shadows reveal a myriad of details on the lunar surface. At low power, you can distinguish most of the lunar disk. Use optional eyepieces with higher magnification to focus on a more limited area.

Lunar Observation Tips

To increase contrast and bring out lunar surface details, use optional filters. A yellow filter improves contrast well, while a neutral density or polarizing filter reduces overall surface brightness and glare.

Observing Planets

The five planets visible to the naked eye are other fascinating targets. You can see Venus go through phases similar to the Moon. Mars sometimes reveals a myriad of surface details and one or both of its polar caps. You can also observe Jupiter's cloud belts and the Great Red Spot (if visible at the time of observation). Additionally, you can see Jupiter's moons orbiting the giant planet. Saturn and its magnificent rings are easily visible at medium power.

Planet Observation Tips

• Remember that atmospheric conditions are usually the determining factor for the amount of detail visible. Therefore, avoid observing planets when they are low on the horizon or directly above a radiating heat source, such as a roof or chimney. Consult the Visibility Conditions later in this chapter.
• To increase contrast and distinguish planet surface details, try using Celestron eyepiece filters.

Observing the Sun

Although the Sun is often overlooked by many amateur astronomers, observing it is both rewarding and fun. However, due to its very high brightness, special precautions must be taken to avoid eye injury or telescope damage.

To safely observe the Sun, use your solar filter to reduce the intensity of sunlight for safe viewing. With a filter, you can observe sunspots moving across the solar disk and faculae, which are bright areas visible on the Sun's edge.

• The best times for Sun observation are early morning and late afternoon, when the temperature is cooler.
• To center the Sun without looking through the eyepiece, observe the shadow of the telescope tube until it forms a circular shadow.

Observing Deep Sky Objects

Deep sky objects are those located outside our solar system. These include star clusters, planetary nebulae, diffuse nebulae, double stars, and other galaxies located outside the Milky Way. Most deep sky objects have a large angular size. A low to medium power telescope is therefore sufficient to observe them. Visually, they are too faint to reveal the colors that appear in long-exposure photographs. They are visible in black and white. And, due to their low surface brightness, they should be observed from a dark spot in the sky. Light pollution around major urban centers obscures most nebulae, making them difficult, if not impossible, to observe. Light pollution reduction filters help reduce background sky brightness, thereby increasing contrast.

Star Hopping (Visual Tracking)

One of the most practical ways to find deep sky objects is by "Star Hopping." Star Hopping is generally done by using bright stars to "guide" you to an object. To successfully star hop, it is useful to know your telescope's field of view. If you are using the standard 20mm eyepiece supplied with the AstroMaster telescope, your field of view is approximately 1°. If you know an object is 3° away from your current position, you simply need to move 3 fields of view. If you are using another eyepiece, consult the chapter on establishing the field of view. Below are instructions for locating two popular objects.

The Andromeda Galaxy (Figure 5-1), also known as M31, is an easy target. To find M31:

1. Locate the constellation Pegasus, a large square visible in the autumn (in the eastern sky, moving towards overhead) and in the winter months (overhead, moving towards the west), and in the winter months (overhead, moving towards the west).
2. Start with the star located in the northeast corner—Alpha (α) Andromedae.
3. Move approximately 7° northeast. You will find two stars of similar brightness—Delta (δ) and Pi (π) Andromedae—about 3° apart.
4. Continue 8° in the same direction. There you will find two stars—Beta (β) and Mu (µ) Andromedae—about 3° apart as well.
5. Move 3° northwest—the same distance as that separating the two stars—towards the Andromeda Galaxy.

Star hopping to the Andromeda Galaxy (M31) is child's play since all the stars that allow you to get there are visible to the naked eye.

Star hopping requires some practice, and objects that do not have nearby stars to distinguish them with the naked eye are more difficult to locate. Among these objects is M57 (Figure 5-2), the famous Ring Nebula. Here's how to find it:

1. First, find the constellation Lyra, a small parallelogram visible in the summer and autumn months. Lyra is easy to spot because it features the bright star Vega.
2. Start with the star Vega—Alpha (α) Lyrae—and move a few degrees southwest to find the parallelogram. The four stars making up this geometric shape are all similar in brightness, making them easy to spot.
3. Locate the two southernmost stars of this parallelogram—Beta (β) and Gamma (γ) Lyrae.
4. Point halfway between these two stars.
5. Move approximately ½° towards Beta (β) Lyrae while staying on a line connecting the two stars.
6. Look through the telescope, and the Ring Nebula should appear in your field of view. The angular size of the Ring Nebula is quite small and difficult to see.
7. Since the Ring Nebula is quite faint, you may need to use "averted vision" to see it. "Averted vision" is a technique that allows you to see an object slightly off to the side. Under these conditions, if you observe the Ring Nebula, center it in your field of view and look to the side. This way, the light from the observed object activates the retinal rods, which only allow black and white vision, rather than the color-sensitive cones. (Remember that when observing faint objects, it is important to be in a dark location, away from street and city lights. The eye needs an average of 20 minutes to fully adapt to darkness. Therefore, always use a flashlight with a red filter to preserve your adaptation to darkness).

These two examples should give you an idea of how to perform Star Hopping to view deep sky objects. To use this method for other objects, consult a star atlas, then do your visual tracking to find the object of your choice using stars visible to the "naked eye."

Figure 5-1: Star chart showing constellations and deep sky objects.

Figure 5-2: Lyra constellation showing Vega and the Ring Nebula (M57).

Visibility Conditions

Visibility conditions affect what you see in the telescope during an observation session. The following conditions affect observation: transparency, sky brightness, and seeing. Understanding observation conditions and their effects on observation will allow you to get the most out of your telescope.

Transparency

Transparency is defined by atmospheric clarity and how it is affected by clouds, humidity, and airborne particles. Thick cumulus clouds are completely opaque, while cirrus clouds can be thin and allow the light from the brightest stars to pass through. Hazy skies absorb more light than clear skies, making faint celestial objects more difficult to see and reducing the contrast of the brightest objects. Aerosols ejected into the upper atmosphere by volcanic eruptions also affect transparency. The ideal is an inky black night sky.

Sky Brightness

Overall sky brightness, due to the Moon, auroras, natural sky glow, and light pollution, greatly affects transparency. While these phenomena do not affect the visibility of the brightest stars and planets, bright skies reduce the contrast of extended nebulae, making them difficult, if not impossible, to distinguish. To optimize your observations, limit your deep-sky astronomy sessions to moonless nights, far from skies polluted by the light of large urban centers. Light pollution reduction filters (RPL filters) improve deep-sky viewing in light-polluted areas by attenuating unwanted brightness while transmitting the luminosity of certain deep-sky objects. You can also observe planets and stars from light-polluted areas or when the Moon is visible.

Seeing

Visibility conditions relate to the stability of the atmosphere and directly affect the amount of fine detail visible in extended objects. The air in our atmosphere acts like a lens that bends and distorts incoming light rays. The curvature's inclination depends on the air's density. The density of different temperature layers varies, affecting the curvature of light rays. Light rays emanating from the same object arrive with a slight offset, creating an imperfect and smeared image. These atmospheric disturbances vary with time and position. The size of air particles relative to your telescope's aperture determines the quality of seeing. When seeing is good, fine details of bright planets like Jupiter and Mars are visible, while stars appear as pinpoint images. When seeing is poor, images are blurry, and stars resemble shimmering blobs.

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

Figure 5-3: Visibility conditions directly affecting image quality. These drawings represent a point source (i.e., a star) under varying seeing conditions from poor (left) to excellent (right). Most often, visibility conditions produce images between these two extremes.

Astrophotography

The AstroMaster series of telescopes was designed for visual observation. After observing the night sky for some time, you may want to photograph it. Several forms of photography are possible with your telescope for celestial and terrestrial tracking. Below is a brief explanation of the different photography methods available, and we suggest consulting books on the subject for detailed information.

You will need, at a minimum, a digital camera or a 35mm SLR. Mount your camera on the telescope using:

• Digital Camera: You will need the universal digital camera adapter (ref. 93626). The adapter allows the camera to be rigidly mounted for terrestrial astrophotography as well as prime focus.
• 35mm SLR Camera: You will need to remove your camera's lens and attach a T-ring adapter specific to your camera's brand. You will then need a T-adapter (ref. 93625) to attach one end of the T-ring to the camera and the other end to the telescope's focuser. The camera's lens is now transformed into a telescope.

Prime Focus and Short Exposure Photography

Prime focus and short exposure photography is the best way to start imaging celestial objects. Simply mount your camera on the telescope as explained above. A few points to keep in mind:

• Perform polar alignment of the telescope and start the optional motor drive for tracking.
• You can capture images of the Moon and bright planets. You will need to experiment with various settings and exposure times. You can find more information in your camera's user manual to supplement the details found in books on the subject.
• Take your photographs from a dark celestial observation site if possible.

“Piggyback” Photography (Mounting the Camera on the Telescope)

Possible only with the 114EQ Newtonian telescope, Piggyback photography is done by mounting the camera and its standard lens on top of the telescope. With this method, you can capture entire constellations and large-scale nebulae. Mount your camera on the Piggyback adapter screw (Figure 6-1) located on top of the tube adapter (your camera must have a threaded hole on the bottom to accept the screw). You will need to perform polar alignment of the telescope and start the optional motor drive for tracking.

Planetary and Lunar Photography with Special Imagers

Recent technology has evolved, making it relatively easy to take superb images of planets and the Moon, with surprising results. Celestron has created the NexImage (ref. 93712), a specialized camera that includes image processing software. From your very first observation night, you can capture planetary images that rival what professionals with large telescopes were doing just a few years ago.

CCD Imaging for Deep Sky Objects

Specialized cameras have been developed for deep sky photography. These items have evolved over the past few years and have become much more affordable, allowing amateurs to take sensational photos. There are also several books explaining how to get the best possible photos. Technology continues to evolve, bringing increasingly powerful and user-friendly products to market.

Terrestrial Photography

Your telescope serves as an excellent telephoto lens for terrestrial photography. You can capture varied panoramas, wildlife, and almost anything else that interests you. You will need to experiment with focusing, shutter speeds, etc., to achieve the best desired image. You can adapt your camera by following the instructions indicated at the top of this page.

Telescope Maintenance

While your telescope requires minimal maintenance, certain precautions are necessary to ensure its optimal performance.

Optical Element Maintenance and Cleaning

Dust and/or moisture may accumulate from time to time on the objective lens or primary mirror, depending on the type of telescope you own. Take the necessary precautions when cleaning the instrument to avoid damaging the optical elements.

If you notice dust on the objective lens, you can remove it with a brush (made of camel hair) or a can of compressed air. Spray for two to four seconds, tilting the can relative to the glass surface. Then, use an optical cleaning solution and a white tissue to remove any residue. Apply a small amount of solution to the tissue, then wipe the optical elements. Make light movements, starting from the center of the objective lens (or mirror) and moving outwards. DO NOT make circular rubbing motions!

You can use a commercial lens cleaner or make your own. An effective cleaning solution can be made with isopropyl alcohol and distilled water. This solution should consist of 60% isopropyl alcohol and 40% distilled water. You can also use dish soap diluted in water (a few drops per liter of water).

Dew may sometimes accumulate on your telescope's optical elements during an observation session. If you wish to continue observing, you must remove the dew, either with a hairdryer (lowest setting) or by pointing the telescope downwards until the dew evaporates.

In case of moisture condensation inside the optical elements, remove the telescope's accessories. Place the telescope in a dust-free environment and point it downwards. This will help eliminate moisture from the telescope tube.

To avoid cleaning your telescope too often, remember to replace the caps on all lenses after use. Since the cells are NOT airtight, caps must be replaced on openings when the instrument is not in use. This helps limit the ingress of contaminants into the optical tube.

Internal adjustments and cleaning must be entrusted to Celestron's after-sales service. If your telescope requires internal cleaning, please contact the factory for a return authorization number and an estimate.

Collimating a Newtonian Telescope

The optical performance of most Newtonian reflector telescopes can be optimized by collimating (aligning) the telescope's optical elements as needed. To collimate the telescope, simply balance its optical elements. Poor collimation will result in optical aberrations and distortions.

Before collimating your telescope, take the time to familiarize yourself with all its components. The primary mirror is the large mirror located at the rear end of the telescope tube. This mirror is adjusted by loosening and tightening the three screws, spaced 120 degrees apart, located at the end of the telescope tube. The secondary mirror (the small elliptical mirror located under the focuser, at the front of the tube) also has three adjustment screws (you will need some optional tools (described below) to perform collimation. To determine if your telescope needs collimation, first point it at a bright wall or outdoors at a blue sky.

Secondary Mirror Alignment

The following procedure describes daytime collimation of your telescope using the optional Newtonian collimation tool (ref. 94183) offered by Celestron. To collimate the telescope without the collimation tool, read the following chapter on night collimation using stars. For very precise collimation, an optional collimation eyepiece of 1½ in (ref. 94182) is available.

If an eyepiece is installed in the focuser, remove it. Fully retract the focuser tube using the focus knobs until the silver tube is no longer visible. You will look into the focuser to see the reflection of the secondary mirror projected by the primary mirror. During this step, ignore the reflection of the primary mirror's outline. Insert the collimation cap into the focuser and look through it. With the focuser fully retracted, you should see the entire primary mirror reflected in the secondary mirror. If the primary mirror is not centered on the secondary mirror, adjust the secondary mirror screws by loosening and tightening them alternately until the primary mirror's periphery is centered in your field of view. DO NOT loosen or tighten the central screw of the secondary mirror support, as it is intended to hold this mirror in its correct position.

Primary Mirror Alignment

You must then adjust the primary mirror screws to re-center the reflection of the small secondary mirror so that the mirror's outline stands out against the primary mirror. When looking into the focuser, the mirror outlines should appear concentric. Repeat steps one and two until this result is achieved.

Remove the collimation cap and look into the focuser, where you should see your eye reflected in the secondary mirror.

The secondary mirror needs adjustment.

The primary mirror needs adjustment.

Figure 7-1: The two mirrors are aligned with the collimation cap in the focuser.

Figure 7-1: The two mirrors are aligned and your eye is looking into the focuser.

Night Collimation Using Stars

After successfully performing daytime collimation, night collimation using stars can be done by precisely adjusting the primary mirror while the telescope tube is mounted and pointed at a bright star. The telescope should be set for night observation, and the star's image should be examined at medium to high magnification (30x to 60x per inch of aperture). If a non-symmetrical focus pattern appears, it may be possible to correct this by re-collimating the primary mirror only.

Procedure (Please read these instructions fully before starting):

To collimate a star in the northern hemisphere, point the instrument at a fixed star such as Polaris. You will find this star in the north sky, at a distance above the horizon equivalent to your latitude. It is also the last star in the handle of the 'Little Dipper' or Ursa Minor. Polaris is not the brightest star in the sky and can sometimes be quite faint, depending on atmospheric conditions.

Before proceeding with primary mirror collimation, locate the collimation screws at the rear of the telescope tube.

The rear cell (illustrated in Figure 7-1) has three large thumbscrews for collimation and three small thumbscrews to lock the mirror in place. The collimation screws are used to tilt the primary mirror. Start by loosening the small thumbscrews a few turns each. Normally, 1/8 of a turn will suffice, and the maximum required for the large collimation screws will not exceed 1/2 to 3/4 of a turn. Unscrew each collimation screw one by one and, using the collimation tool or an eyepiece, examine how the collimation is affected (see the paragraph below). Several attempts may be necessary, but you will eventually achieve the desired alignment.

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

After centering Polaris or a bright star in the field of view, focus using the standard eyepiece or your most powerful eyepiece, i.e., the one with the shortest focal length, such as 6mm or 4mm. The other option is to use a longer focal length eyepiece with a Barlow lens. When the star is sharp, it should appear as a very precise point of light. If, when focusing on the star, it appears irregular or with a luminous halo around the edges, it means your mirrors are misaligned. If you notice a luminous halo on the star that does not move and remains stable when you focus, new collimation will allow for a sharp image.

When you are satisfied with your collimation, retighten the small locking screws.

Figure 7-2: Although the star drawings appear identical on both sides of the focus, they are asymmetrical. The obscuration is shifted to the left side of the diffraction pattern, indicating poor calibration.

Note the direction in which the light appears to increase. For example, if the halo appears at the three o'clock position in the field of view, you must then move the collimation screw or set of screws needed to move the star's image towards the halo. In this example, the goal is to bring the star's image into your eyepiece by adjusting the collimation screws towards the three o'clock position in the field of view. Adjusting a single screw may be enough to sufficiently move the star's image from the center of the field of view about halfway, or less, towards the edge of the field (when using a high-magnification eyepiece).

Collimation adjustments yield better results when observing the star's position in the field of view by simultaneously turning the adjustment screws. This way, you can see exactly in which direction the movement occurs. It may be helpful to do this procedure with two people: one person observes and indicates which screws to turn and by how much, while the other makes the adjustments.

IMPORTANT: After making the first adjustment, or each adjustment, it is necessary to re-aim the telescope tube to bring the star back to the center of the field of view. The symmetry of the star's image can be estimated by moving closer to or further from precise focus and noting the star's pattern. If adequate adjustments are made, an improvement should be seen. Since there are three screws, it may be necessary to adjust at least two of them to achieve the required mirror movement.

Figure 7-3: A collimated telescope should look like a symmetrical ring pattern similar to the diffraction pattern observed here.

Optional Accessories

You will find additional accessories for your AstroMaster telescope that will enhance the quality of your observations while increasing your telescope's utility. Below is a list of various accessories with a brief description. Visit the Celestron website or consult the Celestron Accessories Catalog for detailed descriptions and to learn about all available accessories.

• Sky Maps (ref. 93722): Celestron Sky Maps are the ideal learning guide for the night sky. Even if you already know most of the constellations, these maps help locate many fascinating celestial objects.
• Omni Plossl Eyepieces: Economically priced, these eyepieces provide sharp observations across the entire field of view. These eyepieces have a 4-element lens design and offer the following focal lengths: 4mm, 6mm, 9mm, 12.5mm, 15mm, 20mm, 25mm, 32mm, and 40mm – all with 1.25in (31mm) barrels.
• Omni Barlow Lens (93326): Used with any eyepiece, it doubles the magnification. A Barlow lens is a negative lens that increases a telescope's focal length. The Omni 2x is a 1.25in (31mm) barrel, less than 3in (76mm) long, and weighs only 113g (4oz).
• Lunar Filter (Ref. 94119-A): The lunar filter is an economical 1.25in (31mm) eyepiece filter that reduces the Moon's brightness and improves contrast, allowing more detail to be observed on the Moon's surface.
• Light Pollution Reduction Filter – UHC/RPL (Ref. 94123): This filter is designed to improve the observation of deep-sky astronomical objects from an urban area. The filter selectively reduces the transmission of certain wavelengths of light, particularly those produced by artificial light.
• Night Vision Flashlight (Ref. 93588): This Celestron flashlight with two red LEDs allows for better preservation of night vision than red filters or other systems. Adjustable brightness. Operates on a single 9-volt battery (included).
• Collimation Tool (Ref. 94183): Collimating your Newtonian telescope will be easily accomplished with this practical accessory accompanied by detailed instructions.
• Collimation Eyepiece – 1.25in (31mm) (Ref. 94182): The collimation eyepiece is ideal for precise collimation of Newtonian telescopes.
• Digital Camera Adapter – Universal (Ref. 93626): A universal mounting platform that allows you to do afocal photography (photography through the telescope's eyepiece) using your digital camera's 1.25in eyepieces.
• T-Ring Adapter – Universal 1.25in (31mm) (Ref. 93625): This adapter is intended for your telescope's 1.25in (31mm) focuser. It allows you to attach your 35mm SLR camera for terrestrial photography as well as lunar and planetary photography.

AstroMaster Specifications

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