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Telescope Manual

• Attaching the C8+ Telescope to the Wedge
• Removing the Lens Cap
• Attaching the Accessories
• Moving the Telescope in R.A. and Dec
• Using the Drive
• Image Orientation
• Focusing
• Aligning the Finderscope

The following telescope manual is adapted (with permission) from the telescope manual written by Celestron International, manufacturer of the Celestron 8+ telescopes used for the astronomy labs. Figure 1 identifies the parts mentionned in this manual:

ATTACHING THE C8+ TELESCOPE TO THE WEDGE

For astronomical viewing, you should mount the telescope on the wedge. Since the telescope bases are polar aligned, this will allow you to use the setting circles and the clock drive. To mount the telescope on the wedge:

1. Tilt the telescope on its side and locate the three threaded holes in the bottom of the drive base

2. Partially thread one of the three 3/8-16x1" bolt (supplied in the bolt pack) into the hole that is opposite the rectangular portion of the base.

3. Pick the telescope up by the folk tines and position it above the base as shown in Figure 2.

4. Slide the bolt into the slot on the top of the tilt plate of the wedge.

5. Tighten the bolt slightly so that the bottom of the drive base is flush to the tilt plate. Do not tighten it fully or you will not be able to move the base enough to insert the two remaining bolts. If you do not tighten the bolt at all, the drive base may be tilted slightly preventing the remaining two bolts from threading straight in.

6. Move the base of the telescope until the two remaining holes in the drive base line up with the holes in the tilt plate on the wedge.

7. Insert the screws and tighten all three completely. There is no need to loosen these until you are ready to remove the telescope from the wedge.

REMOVING THE LENS CAP

The C8⁺ lens cap utilizes a bayonet-type locking mechanism to hold it in place. To remove the lens cap, hold the cover firmly and rotate the outer edge 1/2" counterclockwise and pull off.

Once your telescope has been fully assembled, you are ready to attach the accessories and have a look. This section deals with basic telescope operation that is common to all Celestron 8 telescopes.

ATTACHING THE ACCESSORIES

There are several accessories that come standard with all the Celestron 8 telescopes. The installation and use of each of these is described in this section.

The Visual Back

The visual back is the accessory that allows you to attach all visual accessories to the telescopes. To attach the visual back:

1. Remove the rubber cover on the rear cell.

2. Place the knurled slip ring on the visual back over the thread on the rear cell (see Figure 3).

3. Hold the visual back with the set screw in a convenient position and rotate the knurled slip ring clockwise until tight. Once this is done, you are ready to attach other accessories, such as eyepieces, diagonal prism, etc. If you want to remove the visual back, rotate the slip ring counterclockwise until it is free of the rear cell.

The Star Diagonal

The star diagonal is a prism that diverts the light at a right angle to the light path of the telescope. This allows you to observe in positions that are physically more comfortable than if you were to look straight through. To attach the star diagonal:

1. Turn the set screw on the visual back until it no longer extends into (i.e., obstructs) the inner diameter of the visual back.

2. Slide the chrome portion of the star diagonal into the visual back (see Figure 3).

3. Tighten the set screw to hold the star diagonal in place.

If you wish to change the orientation of the star diagonal, loosen the set screw on the visual back until the star diagonal rotates freely. Rotate the diagonal to the desired position and tighten the set screw.

The Eyepieces

The eyepiece, or ocular, is an optical element that magnifies the image focused by the telescope. The eyepiece(s) fits into either the visual back directly (Figure 4), or the star diagonal (Figure 3). To attach an eyepiece:

1. Loosen the set screw on the star diagonal so that it does not obstruct the inner diameter of the eyepiece end of the diagonal.

2. Slide the chrome portion of the eyepiece into the star diagonal (see Figure 3).

3. Tighten the set screw to hold the eyepiece in place. To remove the eyepiece, loosen the set screw on the star diagonal and slide the eyepiece out. You can then replace it with another ocular.

Eyepieces are commonly referred to by focal length. The focal length of each eyepiece is printed on the eyepiece barrel. The longer the focal length (i.e., the larger the number) the lower the eyepiece magnification (i.e., power) and the shorter the focal length (i.e., the smaller the number) the higher the magnification. Generally, you will use low-to-moderate power when viewing. The magnification (or "power") of the telescope is given by:

Magnification = Focal length of telescope / focal length of eyepiece

The Celestron 8 telescope has a 2000 mm focal length and you are provided with two eyepieces of focal length 25 mm and 10mm. According to the above formula, their magnification is 80X and 200X, respectively.

MOVING THE TELESCOPE IN R.A. AND DEC

Pointing the telescope is done by moving the telescope in right ascension, or R.A. for short, and declination, or Dec for short (see Figure 5). Right ascension corresponds to east/west movement while declination corresponds to north/south movement. To make considerable directional changes:

1. Loosen the R.A. and Dec clamps on the mount.

2. Move the telescope until pointing in the desired direction.

3. Lock the R.A. and Dec clamps to hold the telescope in place.

For fine adjustment in declination, simple turn the declination slow motion knob. The Dec clamp does NOT have to be loosened. Once you have the desired target, stop rotating the Dec slow motion knob. If the Dec slow motion knob will not turn, the Dec travel arm may have reached the end of the threaded rod. To correct this, rotate the Dec slow motion knob in the opposite direction until the travel arm is in the center of the fork tine (see Figure 5). Release the Dec clamp and manually center the object you were looking at. Tighten the Dec clamp and Dec slow motion knob will again allow fine adjustments in both directions.

For fine adjustments in right ascension, release the R.A. clamp until the R.A. slow motion knob rotates freely. Turn the R.A. slow motion knob until the desired object is centered. Once centered, tighten the R.A. clamp by turning it clockwise. The clamp must be sufficiently locked for the drive motor to engage and move the telescope. WARNING: DO NOT TURN THE R.A. SLOW MOTION KNOB WHEN THE R.A. CLAMP IS IN THE FULLY LOCKED POSITION. DO NOT FORCE THE FORK MOUNT TO SWIVEL WHEN THE R.A. CLAMP IS FULLY ENGAGED.

The telescope comes equipped with setting circles to help you locate objects in the night sky. The Dec setting circle is incremented in degrees while the R.A. setting circle is incremented in hours and minutes with a marker every five minutes. The numbers on the inner circle are for use in the northern hemisphere while those on the outer circle are for the southern hemisphere.

USING THE DRIVE

The C8⁺ comes with a built-in single motor spur gear clock drive to track objects as they move across the sky. The C8⁺ is DC powered and operated by an internal 9-volt battery. In addition, the C8⁺ has built-in electronics that work as a drive controller allowing you to do long exposure deep-sky astrophotography. Following is a brief description of each function.

Powering Up the Drive

The ON/OFF switch supplies power to the drive motor. Once on, the motor tracks at sidereal rate, that is, the rate at which the stars move across the sky. The LED above the ON/OFF switch illuminates when the drive is on (Figure 7).

In order for the clock drive to track accurately - across the sky from east to west - the telescope must be polar aligned. The process of polar alignment makes the telescope's axis of rotation parallel to the Earth's, ensuring that the telescope moves the right direction. The telescope mounts (and wedges) have been precisely polar aligned so you need not worry about this part of the telescope set up. Keep in mind that the clock drive moves the telescope only in right ascension at a rate that is half of the hour hand on a clock. Therefore, the telescope makes one complete revolution every twenty four hours, so the motion is very hard to detect simply by looking at the telescope.

The drive motor in your C8⁺ is accurate enough to keep objects in the field for long periods. However, if you watch closely, you will notice that the object drifts slowly back and forth in right ascension. This is know as periodic error which all telescopes drives have to some degree. For visual observing, periodic error does not pose a problem.

IMAGE ORIENTATION

It should be noted that the image orientation will change depending on the viewing configuration. When using the star diagonal, the image is right-side-up, but reversed from left-to-right. If inserting the eyepiece into the visual back (i.e., without the star diagonal), the image is inverted (upside down and reversed from left-to-right). This holds true for the 6x30 finderscope as well as the telescope. See Figure 8.

FOCUSING

The primary mirror is mounted on a ring which slides back and forth on the primary baffle tube (Figure 9). The focusing knob, which moves the primary mirror, is on the rear cell of the telescope. To focus, turn the focusing knob until the image is sharp (and small). If the image grows in size as you turn the focus knob, you are turning in the wrong direction. If the knob will not turn, it has reached the end of its travel on the focusing mechanism. Turn the knob in the opposite direction until the image is sharp. Once an image is in focus, turn the knob clockwise to focus on a closer object and counterclockwise for a more distant object (Figure 10). A single turn of the focusing knob moves the primary mirror only slightly. Therefore, it will take many turns (about 40) to go from closer focus (approximately 25 feet) to infinity.

For astronomical viewing out of focus star images are very diffuse making them difficult, if not impossible, to see. In the C8⁺ telescope, a bright star seen far from focus will look like a doughnut. If you turn the focus knob too quickly, you can go right through focus without seeing the image. To avoid this problem, your first astronomical target should be a bright object (like the Moon or a planet) so that the image is visible even when out of focus.

Critical focusing is best accomplished when the focusing knob is turned in such a manner that the mirror moves against the pull of gravity. In doing so, any mirror shift is minimized. This is done by turning the focus knob counterclockwise.

ALIGNING THE FINDERSCOPE

Your Celestron telescope is equipped with a 6x30mm finderscope. The finderscope is designed to help you find objects that are easily overlooked in the main optics of the telescope.

The first number used to describe the finderscope is the power (6X). The second number is the diameter of the objective lens in millimeters.

Incidentally, power is always compared to the unaided human eye. So, a 6X finderscope magnifies images six times more than the human eye.

To make things a little easier, you should align the finderscope during the day when it is easier to locate objects. To align the finder:

1. Choose a conspicuous objects that is over 500 yards away. This will eliminate any possible parallax effect.

2. Point your telescope at the target and center it in the main optics of the telescope.

3. Lock the R.A. and Dec clamps to hold the telescope in place.

4. Check the finderscope to see where the object is located in the field of view.

5. Adjust the screws on the finder bracket, tightening one while loosening another, until the cross hairs are centered on the target.

6. Tighten each screw an additional quarter of a turn until you are sure they will not come loose easily. Make sure that all three screws are tight and hold the finderscope firmly in place. DO NOT OVER TIGHTEN. Accurate alignment of the finder will make it much easier to find objects in the main optical tube.