ENGLISH Omni XLT Series Telescopes INSTRUCTION MANUAL ● Omni XLT 102 ● Omni XLT 102ED ● Omni XLT 120 ● Omni XLT127 ● Omni XLT 150 ● Omni XLT 150R
Table of Contents INTRODUCTION .......................................................................................................................................................... 4 Warning ...................................................................................................................................................... 4 ASSEMBLY ........................................................................................................................................................
Transparency ............................................................................................................................................ 33 Sky Illumination ....................................................................................................................................... 33 Seeing .......................................................................................................................................................
Congratulations on your purchase of an Omni XLT Series telescope. The Omni XLT Series of telescopes come in several different models: 102mm refractor, 102mm ED refractor, 120mm refractor, 150mm refractor, 150mm Newtonian, 127mm Schmidt-Cassegrain. The Omni Series is made of the highest quality materials to ensure stability and durability. All this adds up to a telescope that gives you a lifetime of pleasure with a minimal amount of maintenance.
1 12 2 3 11 4 5 10 6 9 7 8 Figure 1-1 Omni XLT 102 Refractor (Omni XLT 102ED, Omni XLT 120 and Omni XLT 150R refractors are similar) 1. 2. 3. 4. 5. 6. Optical Tube Tube Rings Finderscope Eyepiece Equatorial Mount Latitude Adjustment Screw 7. 8. 9. 10. 11. 12. -5- 1.
1 2 3 4 12 5 11 6 10 7 9 8 Figure 1-2 Omni XLT 150 Newtonian 1. 2. 3. 4. 5. 6. Finderscope Finderscope Bracket Focuser Eyepiece Tube Rings Equatorial Mount 7. 8. 9. 10. 11. 12. -6- 1.
1 12 2 11 3 10 4 9 5 8 6 7 Figure 1-3 Omni XLT 127 Schmidt-Cassegrain 1. 2. 3. 4. 5. 6. Optical Tube Finderscope Finderscope Bracket Equatorial Mount Latitude Scale Accessory Tray/ Leg Brace 7. 8. 9. 10. 11. 12. -7- 1.
This section covers the assembly instructions for your Celestron Omni XLT telescope. The equatorial mount is exactly the same for all the Omni telescope models and the optical tubes have some differences which will be noted. Your Omni telescope should be set up indoor the first time so that it is easy to identify the various parts and familiarize you with the correct assembly procedure before attempting it outdoor. Each Omni telescope comes in two boxes.
Attaching the Equatorial Mount The equatorial mount allows you to tilt the telescope’s axis of rotation so that you can track the stars as they move across the sky. The Omni mount is a German equatorial mount that attaches to the tripod head. On one side of the tripod head there is a metal alignment peg for aligning the mount. This side of the tripod will face north when setting up for an astronomical observing session. To attach the equatorial head: 1.
Attaching the Center Leg Brace Tripod Mounting Knob Central Rod Accessory Tray Accessory Tray Knob Figure 2-6 1. Remove the accessory tray knob and washer from the central rod. 2. Slide the accessory tray over the central rod so that each arm of the tray is pushing against the inside of the tripod legs. 3. Thread the accessory tray knob onto the central rod and tighten. Installing the Counterweight Bar To properly balance the telescope, the mount comes with a counterweight bar and two counterweights.
Since the fully assembled telescope can be quite heavy, position the mount so that the polar axis is pointing towards north before the tube assembly and counterweights are attached. This will make the polar alignment procedure much easier. Installing the Counterweights Each Omni mount comes with two counterweights (One weighs 7 lbs./3.2kg and the other weighs 4 lbs./1.8kg). To install the counterweights: 1. Orient the mount so that the counterweight bar points toward the ground. 2.
5. The DEC slow motion knob attaches in the same manner as the R.A. knob. The shaft that the DEC slow motion knob fits over is toward the top of the mount, just below the telescope mounting platform. Once again, you have two shafts to choose from. Use the shaft that is pointing toward the ground.
Installing the Finderscope To install the finderscope onto the telescope you must first mount the finderscope through the finder bracket and then attach it to the telescope. Toward the rear of the telescope tube (on refractors and Schmidt-Cassegrain) and front of the telescope tube (Newtonian), there is a small bracket with a set screw in it. This is where the finderscope bracket will be mounted. To install the finderscope: 1. 2. 3.
Installing the Star Diagonal The Star Diagonal is a prism that diverts the light at a right angle to the light path of refractors and SchmidtCassegrain telescopes. This allows you to observe in positions that are physically more comfortable than if you looked straight through. To Eyepiece attach the Star Diagonal onto the optical tube of a Schmidt-Cassegrain: 1. Turn the set screw on the visual back until its tip no longer extends into (i.e., obstructs) the inner diameter of the visual back. 2.
The refracting telescopes can use eyepieces and diagonals of a 2” barrel diameter. To use a 2” barrel eyepiece, the 1¼” eyepiece adapter must first be removed. To do this, simply loosen the two chrome thumbscrews located around the focuser barrel (see figure 2-12) and remove the 1 ¼” adapter. Once removed, a 2” eyepiece or accessory can be inserted directly into the focuser barrel and secured with the two thumb screws. Eyepieces are commonly referred to by focal length and barrel diameter.
Balancing the Mount in DEC The telescope should also be balanced on the declination axis to prevent any sudden motions when the DEC clamp (Fig 2-13) is released. To balance the telescope in DEC (all telescopes except the SCT): 1. Release the R.A. clamp and rotate the telescope so that it is on one side of the mount (i.e., as described in the previous section on balancing the telescope in R.A.). 2. Lock the R.A. clamp to hold the telescope in place. 3.
Adjusting the Mount in Altitude • To increase the latitude of the polar axis, tighten the rear latitude adjustment screw and loosen the front screw (if necessary). • To decrease the latitude of the polar axis, tighten the front (under the counterweight bar) latitude adjustment screw and loosen the rear screw (if necessary). The latitude adjustment on the Omni mount has a range from approximately 20° to 60°. It is best to always make final adjustments in altitude by moving the mount against gravity (i.e.
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. Then, the Schmidt-Cassegrain telescope uses both mirrors and lenses. Each optical design is briefly discussed below: Developed in the early 1600s, the refractor is the oldest telescope design.
Figure 3-2 A cutaway view of the light path of the Newtonian optical design The Schmidt-Cassegrain optical system (Schmidt-Cass or SCT for short) uses a combination of mirrors and lenses and s referred to as a compound or catadioptric telescope. This unique design offers large-diameter optics while maintaining very short tube lengths, making them extremely portable. The Schmidt-Cassegrain system consists of a zero power corrector plate, a spherical primary mirror, and a secondary mirror.
Image Orientation The image orientation changes depending on how the eyepiece is inserted into the telescope. When using the star diagonal with refractors and Schmidt-Cassegrains, 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 or the visual back of the SchmidtCassegrain (i.e., without the star diagonal), the image is upside-down and reversed from left-to-right (i.e., inverted).
Aligning the Finderscope Accurate alignment of the finder makes it easy to find objects with the telescope, especially celestial objects. To make aligning the finder as easy as possible, this procedure should be done in the daytime when it is easy to find and identify objects. The finderscope has a spring-loaded adjustment screw that puts pressure on the finderscope while the remaining screws are used to adjust the finder horizontally and vertically.
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.
Up to this point, this manual covered the assembly and basic operation of your telescope. However, 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. The Celestial Coordinate System To help find objects in the sky, astronomers use a celestial coordinate system that is similar to our geographical co-ordinate system here on Earth.
Motion of the Stars The daily motion of the Sun across the sky is familiar to even the most casual observer. This daily trek is not the Sun moving as early astronomers thought, but the result of the Earth's rotation. The Earth's rotation also causes the stars to do the same, scribing out a large circle as the Earth completes one rotation. The size of the circular path a star follows depends on where it is in the sky.
Latitude Scale The easiest way to polar align a telescope is with a latitude scale. Unlike other methods that require you to find the celestial pole by identifying certain stars near it, this method works off of a known constant to determine how high the polar axis should be pointed. The Omni CG-4 mount can be adjusted from about 20 to 60 degrees (see figure 4-3).
Figure 4-4 Remember, while Polar aligning, DO NOT move the telescope in R.A. or DEC. You do not want to move the telescope itself, but the polar axis. The telescope is used simply to see where the polar axis is pointing. Like the previous method, this gets you close to the pole but not directly on it. The following methods help improve your accuracy for more serious observations and photography.
Big Dipper Litle Dipper Cassiopela N.C.P. Polaris (North Star) Pointer Stars Figure 4-6 The two stars in the front of the bowl of the Big Dipper point to Polaris which is less than one degree from the true (north) celestial pole. Cassiopeia, the “W” shaped constellation, is on the opposite side of the pole from the Big Dipper. The North Celestial Pole (N.C.P.) is marked by the “+” sign.
Pointing at Sigma Octantis This method utilizes Sigma Octantis as a guidepost to the celestial pole. Since Sigma Octantis is about 1° degree from the south celestial pole, you can simply point the polar axis of your telescope at Sigma Octantis.. Although this is by no means perfect alignment, it does get you within one degree. Unlike the previous method, this must be done in the dark when Sigma Octantis is visible. Sigma Octantis has a magnitude of 5.
Declination Drift Method of Polar Alignment This method of polar alignment allows you to get the most accurate alignment on the celestial pole and is required if you want to do long exposure deep-sky astrophotography through the telescope. The declination drift method requires that you monitor the drift of selected stars. The drift of each star tells you how far away the polar axis is pointing from the true celestial pole and in what direction.
Aligning the R.A. Setting Circle Before you can use the setting circles to find objects in the sky you need to align the R.A. setting circle. The declination setting circle is aligned during the process of polar alignment. In order to align the R.A. setting circle, you will need to know the names of a few of the brightest stars in the sky. If you don’t, they can be learned by using the Celestron Sky Maps (#93722) or consulting a current astronomy magazine. Figure 4-10 To align the R.A. setting circle: 1.
8. Lock the R.A. clamp to prevent the telescope from slipping in R.A. The telescope will track in R.A. as long as the motor drive is operating. 9. Look through the finderscope to see if you have located the object and center the object in the finder. 10. Look in the main optics and the object should be there. For some of the fainter objects, you may not be able to see them in the finder.
With your telescope set up, you are ready to use it for observing. This section covers visual observing hints for solar system and deep sky objects as well as general observing conditions which will affect your ability to observe. 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. In addition, little or no contrast can be seen during this phase.
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 when observing our star so as not to damage your eyes or your telescope. Never project an image of the Sun through the telescope. Because of the folded optical design (on the SCT), tremendous heat build-up will result inside the optical tube. This can damage the telescope and/or any accessories attached to the telescope.
Seeing Seeing conditions refers to the stability of the atmosphere and directly affects the amount of fine detail seen in extended objects. The air in our atmosphere acts as a lens which bends and distorts 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.
After looking at the night sky for a while you may want to try photographing it. Several forms of photography are possible with your telescope, including terrestrial and celestial photography. Both of these are discussed in moderate detail with enough information to get you started. Topics include the accessories required and some simple techniques. More information is available in various books on the subject matter. Below is described the traditional photographic methods with traditional equipment.
4. Set the shutter speed to the “B” setting and focus the lens to the infinity setting. 5. Locate the area of the sky that you want to photograph and move the telescope so that it points in that direction. 6. Find a suitable guide star in the telescope eyepiece field of view. This is relatively easy since you can search a wide area without affecting the area covered by your camera lens.
2. Center the Moon in the field of your telescope. 3. Focus the telescope by turning the focus knob until the image is sharp. 4. Set the shutter speed to the appropriate setting (see table 6-1). 5. Trip the shutter using a cable release. 6. Advance the film and repeat the process.
1. Find and center the desired target in the viewfinder of your camera. 2. Turn the focus knob until the image is as sharp as possible. 3. Place the black card over the front of the telescope. 4. Release the shutter using a cable release. 5. Wait for the vibration caused by releasing the shutter to diminish. Also, wait for a moment of good seeing. 6. Remove the black card from in front of the telescope for the duration of the exposure (see accompanying table). 7.
Note: Digital Cameras – follow the camera instructions on focusing and shutter data. 1. Polar align the telescope. For more information on polar aligning see the Polar Alignment section earlier in the manual. 2. Remove all visual accessories. 3. Thread the Radial Guider onto your telescope. 4. Thread the T-Ring onto the Radial Guider. 5. Mount your camera body onto the T-Ring the same as you would any other lens. 6. Set the shutter speed to the "B" setting. 7. Focus the telescope on a star. 8.
CCD Imaging for Deep Sky Objects Special cameras have been developed for taking images of deep sky images. These have evolved over the last several years to become much more economical and amateurs can 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 on the market. Terrestrial Photography Your telescope makes an excellent telephoto lens for terrestrial (land) photography.
While your telescope requires little maintenance, there are a few things to remember that will ensure your telescope performs at its best. Each optical design type has special collimation instructions described below. Care and Cleaning of the Optics Occasionally dust and/or moisture may build up on the objective lens, the corrector plate, or primary mirror depending on which type of telescope you have. Special care should be taken when cleaning any instrument so as not to damage the optics.
Pick a bright star and center it in the field of the telescope. Study the image of the star while racking it in and out of focus using an eyepiece that yields 30 to 60 power for every inch of aperture. If an unsymmetrical focus pattern is present, then collimation is necessary. (If the telescope is properly collimated, the out of focus star image will appear as a concentric ring pattern similar to that shown in Figure 7-2). To collimate, the telescope should be on either a motor driven (i.e.
Before you begin the collimation process, be sure that your telescope is in thermal equilibrium with the surroundings. Allow 45 minutes for the telescope to reach equilibrium if you move between large temperature extremes. To verify collimation, view a star near the zenith. Use a medium to high power ocular — 12mm to 6mm focal length. It is important to center a star in the center of the field to judge collimation. Slowly cross in and out of focus and judge the symmetry of the star.
Perfect collimation will yield a star image very symmetrical just inside and outside of focus. In addition, perfect collimation delivers the optimal optical performance specifications that your telescope is built to achieve. If seeing (i.e., air steadiness) is turbulent, collimation is difficult to judge. Wait until a better night if it is turbulent or aim to a steadier part of the sky. A steadier part of the sky is judged by steady versus twinkling stars.
Newtonian collimation views as seen through the focuser using the collimation cap Primary mirror needs adjustment Secondary mirror needs adjustment Secondary Mirror Primary Mirror Both mirrors aligned with the collimating cap in the focuser. Mirror Clip 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 nonsymmetrical focus pattern is present, then it may be possible to correct this by re-collimating only the primary mirror.
When satisfied with the collimation, tighten the small locking screws. Figure 7-7 Even though the star pattern appears the same on both sides of focus, they are asymmetric. The dark obstruction is skewed off to the left side of the diffraction pattern indicating poor collimation. Take note of the direction the light appears to flare.
You will find that additional accessories for your Omni telescope will enhance your viewing pleasure and expand the usefulness of your telescope. This is just a short listing of various accessories. Visit the Celestron website for complete and detailed accessories available. Barlow Lens - A Barlow lens is a negative lens that increases the focal length of a telescope. Used with any eyepiece, it doubles the magnification of that eyepiece. Celestron offers several Barlow lenses in the 1-1/4" size.
Flashlight, Night Vision - (# 93588) - Celestron’s premium model for astronomy, using two red LED's to preserve night vision better than red filters or other devices. Brightness is adjustable. It operates on a single 9 volt battery (included). Diagonal 2" Mirror (# 93519) - Celestron offers a 2" 90° Mirror Diagonal to thread on Schmidt- Cassegrain telescopes or slides into the barrel of a 2" refractor focuser. This diagonal includes an adapter to accept 1¼" eyepieces.
Reducer/Corrector (# 94175) - This lens reduces the focal length of the SCT telescope by 37%, making your Omni XLT127 a 788mm f/6.3 instrument. In addition, this unique lens also corrects inherent aberrations to produce crisp images all the way across the field when used visually. When used photographically, there is some vignetting that produces a 26mm circular image on the processed film. It also increases the field of view significantly and is ideal for wide-field, deep-space viewing.
Appendix A Technical Specifications Omni XLT Series Optical Design Aperture Focal Length Focal Ratio Optical Coatings 21088 21092 21090 21094 31057 11084 Omni XLT 102 Omni XLT 102ED Omni XLT 120 Omni XLT 150R Omni XLT 150 Omni XLT 127 Refractor Refractor Refractor Refractor Newtonian Schmidt-Cassegrain 102mm (4.0") 102mm (4.0") 120mm (4.7") 150mm (6.0") 150mm (6.0") 127mm (5.0") 1000mm 900mm 1000mm 750mm 750mm 1250mm f/10 f/9 f/8.
Appendix B - Glossary of Terms AAbsolute Magnitude Airy Disk Alt-Azimuth Mounting Altitude Aperture Apparent Magnitude Arc minute Arc second Asterism Asteroid Astrology Astronomical Unit (AU) Aurora Azimuth BBinary Stars The apparent magnitude that a star would have if it were observed from a standard distance of 10 parsecs, or 32.6 light-years. The absolute magnitude of the Sun is 4.8, at a distance of 10 parsecs, it would just be visible on Earth on a clear moonless night away from surface light.
FFocal Length JJovian Planets KKuiper Belt The distance between a lens (or mirror) and the point at which the image of an object at infinity is brought to focus. The focal length divided by the aperture of the mirror or lens is termed the focal ratio. Any of the four gas giant planets that are at a greater distance from the sun than the terrestrial planets. A region beyond the orbit of Neptune extending to about 1000 AU which is a source of many short period comets.
RReflector Resolution Right Ascension: (RA) SSchmidt Telescope Sidereal Rate TTerminator UUniverse VVariable Star WWaning Moon Waxing Moon ZZenith Zodiac A telescope in which the light is collected by means of a mirror. The minimum detectable angle an optical system can detect. Because of diffraction, there is a limit to the minimum angle, resolution. The larger the aperture, the better the resolution.
Celestron Two Year Warranty A. Celestron warrants this telescope to be free from defects in materials and workmanship for two years. Celestron will repair or replace such product or part thereof which, upon inspection by Celestron, is found to be defective in materials or workmanship. As a condition to the obligation of Celestron to repair or replace such product, the product must be returned to Celestron together with proof-of-purchase satisfactory to Celestron. B.
Celestron 2835 Columbia Street Torrance, CA 90503 U.S.A. Tel. (310) 328-9560 Fax. (310) 212-5835 Website www.celestron.com Copyright 2008 Celestron All rights reserved. (Products or instructions may change without notice or obligation.) Item # 21088-INST Rev. 02 Printed in China $10.