Celestron CGEM 800 - Manual

10 A A t t t t a a c c h h i i n n g g t t h h e e V V i i s s u u a a l l B B a a c c k k The visual back is the accessory that allows you to attach all visual accessories to the telescope. The telescope optical tubes come with the visual back installed. If it is not already on the tube it can be a...

11 I I n n s s t t a a l l l l i i n n g g t t h h e e F F i i n n d d e e r r s s c c o o p p e e The CGEM 800 and 925 telescopes come with a 6x30 finderscope used to help you locate and center objects in the main field of your telescope. To accomplish this, the finder has a built-in cross-hair ret...

12 3. Place the mounting bracket over the two holes of the rear cell as shown in the figure 2-10. 4. Insert the screws through the bracket and into the rear cell. WARNING : If you remove the mounting bracket, do not completely thread the screws back into the rear cell of the telescope. The screws ma...

13 2. Point your telescope at the object you selected and center it in the main optics of the telescope. 3. Lock the azimuth and altitude clamps to hold the telescope in place. 4. Check the finder to see where the object is located in the field of view. 5. Adjust the thumb screws on the finder brack...

14 B B a a l l a a n n c c i i n n g g t t h h e e M M o o u u n n t t i i n n D D E E C C Although the telescope does not track in declination, the telescope should also be balanced in this axis to prevent any sudden motions when the DEC lock lever is loose. To balance the telescope in DEC: 1. Loos...

15 The latitude adjustment on the mount has a range from approximately 15° to 70°. It is best to always make final adjustments in latitude by moving the mount against gravity (i.e. using the rear latitude adjustment screw to raise the mount). Adjusting the Mount in Azimuth For rough adjustments in a...

16 All Celestron computerized telescope come with a hand control designed to give you instant access to all the functions that your telescope has to offer. With automatic slewing to over 40,000 objects, and common sense menu descriptions, even a beginner can master its variety of features in just a ...

17 4. Catalog Keys: The hand control has keys on the hand control to allow direct access to each of the catalogs in its database. The hand control contains the following catalogs in its database: Messier – Complete list of all Messier objects. NGC – Complete list of all the deep-sky objects in the R...

18 the telescope will automatically slew to. One Star Align uses the same time/location information but only uses one star for alignment. Solar System Align will display a list of visible daytime objects (planets and the moon) available to align the telescope. Quick-Align will ask you to input all t...

20 O O n n e e S S t t a a r r A A l l i i g g n n One-Star Alignment works much the same way as Two-Star Align but uses only a single star in the sky for alignment. This method of alignment is not as accurate as the two-star alignment and is recommended only for telescopes that are permanently and ...

21 L L a a s s t t A A l l i i g g n n m m e e n n t t The Last Alignment method will automatically recall the last stored index positions to continue using the alignment that was saved when the telescope was last powered down. This is a useful feature should your telescope accidentally lose power o...

22 Pressing any of the other catalog keys (M, CALD, NGC, or STAR) will display a blinking cursor below the name of the catalog chosen. Use the numeric key pad to enter the number of any object within these standardized catalogs. For example, to find the Orion Nebula, press the "M" key and en...

23 Direction Buttons The hand control has four direction buttons (3) in the center of the hand control which control the telescope's motion in altitude (up and down) and azimuth (left and right). The telescope can be controlled at nine different speed rates. Rate Button Pressing the RATE key (11) al...

24 Tracking Rate In addition to being able to move the telescope with the hand control buttons, your telescope will continually track a celestial object as it moves across the night sky. The tracking rate can be changed depending on what type of object is being observed: Sidereal This rate compensat...

25 To replace the contents of any of the user defined objects, simply save a new object using one of the existing identification numbers; the telescope will replace the previous user defined object with the current one. Get RA/DEC - Displays the right ascension and declination for the current positi...

26 Anti-backlash – All mechanical gears have a certain amount of backlash or play between the gears. This play is evident by how long it takes for a star to move in the eyepiece when the hand control arrow buttons are pressed (especially when changing directions). The CGEM anti-backlash features all...

27 and clockwise (negative altitude) then make sure that the buttons used to center the alignment stars also move the telescope in the same directions. Autoguide Rate – Allows the user to set an autoguide rate as a percentage of sidereal rate. This is helpful when calibrating your telescope to a CCD...

28 RA Limits - Sets the limits that the telescope can slew or track in Right Ascension (R.A.) before stopping. The slew limits are represented in degrees and by default set to 0º, being the position of the telescope when the counterweight bar is extended out horizontally. However, the slew limits ca...

29  R.A. switch - this procedure records the offset error when the right ascension index mark is aligned at start-up. Calibrating the R.A. Index will improve the accuracy of your initial star alignments when aligning the telescope in the future.  GoTo Calibration – Goto Calibration is a useful too...

30 Scrolling Menu This menus allows you to change the rate of speed that the text scrolls across the hand control display.  Press the Up (number 6) button to increase the speed of the text.  Press the Down (number 9) button to decrease the speed of the text. Set Mount Position The Set Mount Positi...

32 Figure 4-1 A A c c u u t t a a w w a a y y v v i i e e w w o o f f t t h h e e l l i i g g h h t t p p a a t t h h o o f f t t h h e e S S c c h h m m i i d d t t - - C C a a s s s s e e g g r r a a i i n n o o p p t t i i c c a a l l d d e e s s i i g g n n Actual image orientation as seen with ...

33 Figure 4-3 - The emblem on the end of the focus knob shows the correct rotational direction for focusing your telescope . Focusing The Schmidt-Cassegrain focusing mechanism controls the primary mirror which is mounted on a ring that slides back and forth on the primary baffle tube. The focusing k...

34 thousand yards. The apparent field of each eyepiece that Celestron manufactures is found in the Celestron Accessory Catalog (#93685). 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 throug...

35 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 ...

36 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 ...

37 Latitude Scale Polar Aligning the Mount Latitude Scales 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 p...

38 2. Then accurately center the star in your eyepiece and press ALIGN. The telescope will then "sync" on this star and slew to the position that star should be if it were accurately polar aligned. 3. Use the mounts latitude and azimuth adjustments (see figure 2-15) to place the star in the ...

39 Polar Finderscope Cover Polar Axis Cover Figure 5-4 photography. This must be done in the dark when Polaris is visible and can be done using the hole in the polar axis or with the help of the optional polar axis finderscope. See Optional Accessory section. 1. Set the telescope up so that the pola...

40 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 which will affect your ability to observe. Observing the Moon Often, it is tempting to look at the Moon ...

42 Figure 6-1 Seeing conditions directly affect image quality. These drawings represent a point source (i.e., star) under bad seeing conditions (left) to excellent conditions ( right). Most often, seeing conditions produce images that lie some where between these two extremes.

43 After looking at the night sky for a while you may want to try photographing it. Several forms of celestial photography are possible with your telescope, including short exposure prime focus, eyepiece projection, long exposure deep sky, terrestrial and even CCD imaging. Each of these is discussed...

44 1. Load your camera with film that has a moderate-to-fast speed (i.e., ISO rating). Faster films are more desirable when the Moon is a crescent. When the Moon is near full, and at its brightest, slower films are more desirable. Here are some film recommendations:  T-Max 100  T-Max 400  Any 100...

46 Once you have mastered the technique, experiment with different films, different focal length eyepieces, and even different filters. Long Exposure Prime Focus Photography This is the last form of celestial photography to be attempted after others have been mastered. It is intended primarily forde...

47  3M 1000 (color slide)  Scotchchrome 400  T-Max 3200 (black and white print)  T-Max 400 (black and white print) Periodic Error Correction (PEC) PEC for short, is a system that improves the tracking accuracy of the drive by reducing the number of user corrections needed to keep a guide star ce...

48 7. Point the telescope at the object you want to photograph and center the guide star on the illuminated cross hairs and you are ready to play back the periodic error correction. 8. Once the drive's periodic error has been recorded, use the Playback function to begin playing back the correction f...

50 F F i i g g u u r r e e 8 8 - - 1 1 The three collimation screws are located on the front of the secondary mirror housing. While your telescope requires little maintenance, there are a few things to remember that will ensure your telescope performs at its best. Care and Cleaning of the Optics Occ...

51 Figure 8-3 A collimated telescope should appear symmetrical with the central obstruction centered in the star's diffraction pattern. 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 e...

53 You will find that additional accessories enhance your viewing pleasure and expand the usefulness of your telescope. For ease of reference, all the accessories are listed in alphabetical order. Barlow Lens - A Barlow lens is a negative lens that increases the focal length of a telescope. Used wit...

55 Reducer/Corrector (#94175) - This lens reduces the focal length of the telescope by 37%, making your C8-S a 1280mm 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...

56 Appendix A – Technical Specifications CGEM Series 11097 11098 11099 CGEM 800 CGEM 925 CGEM 1100 Specifications: Optical Design 203mm (8") Schmidt- Cassegrain 235mm (9.25") Schmidt- Cassegrain 280mm (11") Schmidt- Cassegrain Focal Length 2032mm F/10 2350mm F/10 2800mm F/10 Finderscope ...

57 Appendix B - Glossary of Terms A - Absolute magnitude 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 ...

60 Appendix C - RS-232 Connection You can control your telescope with a computer via the RS-232 port on the computerized hand control and using an optional RS-232 cable (#93920). Once connected, the telescope can be controlled using popular astronomy software programs. Communication Protocol: The CG...

61 Additional RS232 Commands S S e e n n d d A A n n y y T T r r a a c c k k R R a a t t e e T T h h r r o o u u g g h h R R S S 2 2 3 3 2 2 T T o o T T h h e e H H a a n n d d C C o o n n t t r r o o l l 1. Multiply the desired tracking rate (arcseconds/second) by 4. Example: if the desired trackra...

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...