Celestron 5" Usage Notes

Last revised: June 11, 2005
presented by:
 www.Pietro.org

Author is not affiliated with, and these notes are not authorized by, Celestron International. 
Latest version is found at “The Unofficial Home for Celestron 5” SCTs”.

Introduction

These notes serve as a concise reference for common Celestron 5" SCT setup and maintenance tasks -- without the need to wade through plethora of manuals and instruction pages you have accumulated over the years. Information was culled from Celestron manuals, and user experience. The occasional observer, who may loose familiarity with the equipment over time, will find the tips and hints here a real time-saver. Seasoned observers may learn a thing-or-two about their equipment. Print these notes (adjust browser font size first) and keep them packed with your observing gear for quick reference! 

Being concise, these notes are not a complete substitute for reading the telescope and accessories literature: reference is made to that literature when necessary. 

Test any nighttime procedures under lighted conditions the first time you try them.  Celestron has neither reviewed nor endorsed these notes. Use this information at your own discretion.

I'd like to expand this reference, so send your thoughts and tips to webmaster@pietro.org. Submission of  NexStar tips for posting is especially encouraged.  Links to other sites, with their own tips, modifications, etc., can be found on the website.

CONTENTS

Telescope Field Setup
Setup Optional Tripod for Equatorial Fork-Mount (C5/C5+)
Placing on the CG-3 Mount (G5 and others)*
Orange Tube on Alternate Mounts (Orange Tube)
External Power Sources (All Models)
Align the Finder Scope (All Models so equipped)
Rough Polar Alignment (C5/C5+)
Fine Polar Alignment (All Equatorial Models)
Calibrate RA Setting Circle (All Equatorial Models)
Align the Internal Optics (All Models)
Disassembly at End of Observing Session (C5/C5+)

General Usage Notes
Slow Motion and Axis Locks (Orange Tube, C5/C5+)*
Hand Controller (C5/C5+)*
RA Motor Drive Direction Change (C5/C5+)* 
Focusing (All Models)*
Reducer/Corrector (All Models)
Image Orientation (All Models)*
Prime Focus Photography (All Models)
Photography Counterweight (C5/C5+)

Telescope Maintenance
Cleaning Fluid for External Optics (All Models)
Corrector Plate Removal (All Models?)*
Base Maintenance (C5/C5+)
Tripod Maintenance (C5/5+ but can apply to all tripod mounted scopes) 
Diagonal Testing (All Models) 
Declination Setting Circle Care (All models so equipped)*

Telescope Field Setup

Setup Optional Tripod for Equatorial Fork-Mount (C5/C5+)

• Orient the tripod so the wedge support holes form a triangle pointing south.  This will minimize azimuth reorientation when polar alignment is done.

• Extend the tripod legs at least a few inches each, if not all the way.  Lowering the legs to achieve level (last step) is easier than extending the legs, when the weight of the telescope and wedge are attached.

• Follow direction in users manual to mount wedge to tripod and telescope base to wedge.

• Turn the declination knob to place the tangent arm (running down the inside of the fork) in the middle of the threaded declination rod.

• Mount telescope onto the fork as instructed in the manual.

• Using the bubble-level on the wedge, experiment with lowering the legs to achieve level.

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Placing on the CG-3 Mount (G5 and others that mount on CG-3)

To make mounting the optical tube on the CG-3 mount easier: remove the slow motion declination knob so it doesn't interfere with your hand, when attaching the mounting screws. The tube should be mounted on the platform so the front (corrector end) is away from the declination slow-motion knob.

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Orange Tube on Alternate Mounts (Orange Tube)

If you demount the C5 from the "saddles" that go between it and the fork, tape-up the exposed tube holes to protect the optics. Simply replacing the screws on the un-mounted tube - without the intervening tube "saddle" - will protrude the screws too far into the interior of the telescope and damage the optics.

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External Power Sources (All Models)

Plug connector into telescope base before connecting to power outlet.

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Align the Finder Scope (All Models so Equipped)

Telescope must be on a sturdy mount/tripod to do this.

• Mount the visual back on the main telescope without any intervening accessory, such as diagonal or field flattener.

• If the finder has never been aligned before, place a low-power eyepiece in the telescope visual back and sight a bright star, the Moon, or distant ground structure.  First align the finder cross-hair with the telescope axes of motion.  Look though the finder and move one of the telescope slow-motion controls back and forth.  Rotate the finder to line-up the cross-hair with this motion: push finder forward to pop out the O-ring, align, and pull back.  With that done, keep looking through the finder and rough-align on the target by turning the set screws that ring the finder holder.  Turn screws two-at-a-time: tighten one and loosen the other. 

• Fine-tune alignment though a higher-power eyepiece, by repeating the above step on a bright star.  Use a guiding (cross-hair) eyepiece here, if you have one.

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Rough Polar Alignment (C5/C5+)

The initial steps above must be completed to proceed with this one.  Caution!  Moving the wedge in altitude (raising/lowering) can be tricky, because of the weight of the telescope tube.  Loosen wedge altitude and azimuth restraining bolts just enough to move the scope – leave some friction!

• Set wedge roughly to latitude of site.
• Place diagonal and eyepiece (cross-hair, if available) in visual back.
• Set scope to 90-degree declination and lock declination axis.
• Move scope in right ascension (RA) so that fork arm is at the lowest spot and lock RA rotation axis.
• Moving the scope around often causes the ground/tripod to settle, so this is a good time to re-level the tripod if you are using one.  Observe the bubble-level while lowering one leg (slightly) at a time.  Perfect level is important if you plan multiple sessions at the same location and do not change the angle on your wedge between sessions.  This will insure that the polar axis angle is consistent from session-to-session and require less fine-tuning on subsequent setup.
• Center finder on Polaris by moving wedge in altitude and azimuth (side-to-side) – don’t move RA or DEC axis.  Moving the wedge, with the factory-supplied hardware, is accomplished by loosening and tightening several hex bolts with an allen key.  Be aware that it is awkward to grip the telescope and move it in alt/azimuth because there are no handgrips!  Locking the RA and using the fork handle to move the weight of the scope can damage the RA gears.  With the lock off it is hard to move without causing it to slip.  Moving the scope by the piggyback platform will likewise stress the fork arm.  (I recommend hardware modifications to replace the hex bolts with wing nuts or knobs.  This will void your tripod and wedge warranty.  Modification instructions will be posted on this site in the future.) 
• Finish centering on Polaris by sighting it through the main telescope eyepiece while making slight alt/azimuth adjustments with the wedge.

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Fine Polar Alignment (All Equatorial Models)

This is can be TEDIOUS for beginners and you may wish to skip this step, if you are not imaging through the main tube.  Two methods are presented below to fine tune alignment. 

 Alignment by Polar Offset

The steps below assume the equatorial mounted telescope is set to 90-degree declination and the mount was moved in alt/azimuth to center Polaris though the main telescope (steps above for C5/C5+):

• At this point the scope is aligned on Polaris and not the celestial pole.  Before finding the pole, the alignment of the declination axis must be fine-tuned.  With Polaris centered in a low-power eyepiece, unlock the RA axis and slew the scope in RA while observing Polaris.  Polaris will stay centered if the declination axis is truly at a right angle (90-degrees) to your RA axis.  If the declination axis is slightly off, the star will make a small circle.  If further off, it may appear to move in a nearly straight line.  If the axis is off: move the slow-motion declination control a partial turn – remember the direction -- while keeping Polaris in view.  If you turned in the correct direction, Polaris should make a tighter circle around the center of the field as the telescope is rotated in RA.  If Polaris quickly flies out of the field faster than before, you must adjust the slow-motion declination control the other way.  For large corrections you may have to adjust the mount in alt/azimuth to keep Polaris into the field-of-view.  Keep adjusting until Polaris stays in the field under RA rotation.  If you succeed, loosen the polar setting circle disk (use a Philips screwdriver) and align the index with the 90-degree mark, before tightening it.
• Fine tune polar alignment by using a low-power eyepiece and a map of the region around Polaris or computer program that indicates angle offset of Polaris from the pole (The Astro Utilities on this site can generate an image of Polaris in relation to the pole for any date and time).  One handy way I’ve used is to photocopy a detailed map (Uranometria quality) of the pole stars onto transparency.  Flip the transparency upside-down and tape to a white sheet of cardboard.  This will give you the required mirror-reversed image of the polar region to center the guiding eyepiece on.  Digitized or computer generated sky charts can be employed to generate a similar view.  Move the telescope in altitude and azimuth to offset Polaris the required amount to match the map or calculated angle offset.
• To minimize error caused by misalignment of declination axis: if Polaris is near an upper/lower culmination, rotate telescope in RA so that tube is above or below the RA axis (set fork arm low or high on C5/C5+).  Now achieve polar alignment by offsetting in altitude away from Polaris.  If Polaris is near east/west alignment rotate tube to be on left or right side of scope and offset mount in azimuth.

Alignment Using Drift Method

This should be done after rough polar alignment. 

• With clock-drive off, center a star on the celestial equator near the meridian.  Watch drift in declination to determine correction to polar axis.  Moving the equatorial mount in azimuth will correct the drift.

If drift is south: axis is too far east
If drift is north: axis too far west

• Now move in RA to a star near the eastern horizon and check its motion to see if the polar axis is set to the proper altitude.  Moving the equatorial mount in altitude will correct the drift.  Switch the following error corrections for a star on western horizon.

If drift is south: axis is too low
If drift is north: axis too high

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Calibrate RA Setting Circle (All Equatorial Models)

• Make sure clock drive is on.  Chose a bright star near the celestial equator and center in telescope eyepiece.  Dial in RA of star on setting circle -- see chart.  For the C5/C5+ use the inner markings in the northern hemisphere; increments are 5-minutes of RA so try to choose a star with RA minutes that is a multiple of 5. 

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Align the Internal Optics (All Models)

• When seeing is steady and scope is thermally stable, you can check alignment of the optics by employing the collimation method found in the manual (I have preference for the hi-power technique).  This technique requires sighting a star and adjusting the three screws that align the secondary mirror at the front of the telescope. (Since this invariably places a metal tool near the corrector lens, I think this is best done with two people -- though I've never tried it this way(!): one person to turn the adjustment screws and the other to watch the calibration star and recenter it.)  Use an eyepiece directly into the visual back, without flattener or diagonal, so that you are not correcting for defects in these devices.  Keep the clock-drive on and aim at a star that is at a comfortable elevation.  During collimation you’ll notice that the star moves around when an adjustment screw it turned. This will impact your Polar alignment slightly.

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Disassembly at End of Observing Session (C5/C5+)

• Turn off clock drive, place eyepieces back in case, and place caps on scope and finder optics.

• Remove scope from fork by sliding it off the dovetail bracket on the declination axis, as described in the manual.  Store the telescope. 

• With the weight off the scope, you can carry the whole tripod, wedge and drive base away.  Else break each piece down and move separately.

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General Usage Notes

Slow Motion and Axis Locks (Orange Tube, C5/C5+)

RA slow motion

• Do not force the RA slow motion if the axis is fully locked. Slow motion in RA is only possible if the RA lock is partially or fully loose. Use the partial setting -- you'll feel the slow motion to be slightly stiff -- when making small motions. Fully loosen for large motions. If the RA circle is calibrated and the drive is on: each second the lock is fully loose will cause the RA circle to fall behind by a like amount.

Declination slow motion

• Orange Tube: you must lock the declination axis for the slow motion control to work.
• C5/C5+: declination slow motion works regardless of the declination axis lock.

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Hand Controller (C5/C5+)

The hand controller sends signals to an integrated circuit chip in the drive base. This chip sends pulse-modulated signals to the motors. Because of this computer control, various drive functions of the hand controller exist -- depending on the version of the chip is in the drive base. It is known that the documentation shipped with scopes might not have been up-to-date on these control features. You'll have to try the following tests to see which features are active in your model. These tests can be done in daylight, with the hand controller plugged into the base, and the scope doesn't have to be mounted on the arm.

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RA Motor Drive Direction Change (C5/C5+) 

See Hand Controller section to see if this is necessary. If your model lacks the drive reversal feature, follow this instructions.

• Remove the drive base cover by unscrewing the four larger screws at the corners of the plate.  (Do not undo the four smaller screws! They hold a circuit board in place).  
• Locate the red and black wire pair that runs from the circuit board to the motor. On the circuit board it ends in a two pin connector. 
  Do not continue if your version of the C5+ does not have this connection, use the Hand Controller method of flipping the motor direction instead.
• If the red and black wire connector exists: unplug from the circuit board, flip the connector over and plug it back in. In the end, the red and black wire have traded places and the RA motor should track for southern hemisphere operation.

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Focusing (All Models)

To keep mirror from shifting due to gravity, the last focus turn should be counter-clockwise with the tube pointed at the sky.  This is the direction of the infinity arrow on the focus knob.

Orange Tube: At "high-power," a position shift of one-third the field may be noticed while focusing. This is due to the primary mirror wobbling while moving on its track.

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Reducer/Corrector (All Models)

With this accessory in place, after focusing on a star at field center, Celestron recommends turning the knob an additional 30-degrees to get sharp focus across the field.  Alternately set a target star between the center and edge of field to focus on.  

Don’t use an eyepiece longer than 35-mm with this accessory.

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Image Orientation (All Models)

• Image in finder is upside-down and mirror L<=> R reversed: star chart matches if turned "upside-down".  
• Image in main scope, with eyepiece inserted directly into visual back, matches finder.
• Image in main scope with diagonal is right-side-up and L<=> R reversed: star chart matches if you look through the "back" of the chart.

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Prime Focus Photography (All Models)

When using the Reducer/Corrector in photography, Celestron recommends turning the focus knob an additional 15-degrees after the center of field is in sharp focus.  Without the Reducer/Corrector, this amount should be 30-degrees.

If you will be using the Reducer/Corrector, mount it on the scope first and then follow the directions below.

T-Adapter Unguided Photography
Assemble components in this order: thread T-Ring onto T-Adopter and mount to camera body.  Mount whole assemblage onto scope.  Find scope balance by setting the tube horizontal and sliding it back and forth along the dovetail mount.

Radial Guider Photography
Prepare the Guider
Instructions here were tested using the Celestron Radial Guider #94171 -- not the '-5' model!  Using this with a Celestron 5" SCT requires that the spacing ring on the shaft of the eyepiece holder be removed.  This ring is 5-mm thick and located below the eyepiece holder in contact with the body of the guider.  Above it are two hex set screws.  Loosen these screws with an Allen wrench (not provided, but if you bought all the accessories you will have one wrench that fits) and slowly lift out the eyepiece holder -- mind the optical prism at the end of this assembly!  Put the spacer ring aside and replace the assembly.  Re-alignment of the eyepiece-holder/prism assembly is best done when the guider is mounted on the telescope and is explained at the bottom. 

Mount the Parts
The guider setup puts a lot of weight on one side of the telescope tube, so move the scope as far forward in the dovetail bracket as possible before connecting the following parts: attach the radial guider to telescope; mount T-Ring onto this; mount camera onto T-Ring.  Position eyepiece holder so it is above the vertical axis of the film plane.  Insert guiding eyepiece into holder.

Check Clearance
With the Reducer/Corrector as part of the assemblage, there may not be enough space between the back of the camera and the mount base to reach the northern parts of the sky.  Slowly swing the telescope in declination to see if there is clearance - if not: read off the maximum declination from the setting circle and compare with your intended photographic targets.  If the targets are out of range, remove one of the tripod block safety screws and slide the telescope forward along the dovetail bracket until you have clearance.  Try replacing the screw.  If you get less than three turns of the screw, leave off to avoid loosing it.

Balance the Telescope
The telescope will probably be out of balance, especially if you used the Reducer/Corrector and a heavy camera.  If you planned on employing a second camera on the piggyback platform, attach it now and balance the scope by sliding it along the track of the platform.  If not, and you have the optional Counterpoise set (#93603), attaching the big counterweight onto the piggyback platform works nicely.  Using the 1/4x20 mounting screw and washers on either side of the platform, mount the counterweight bar as you would a camera and then spin-on the big weight until it contacts the platform.  Move this assemblage along the platform to balance the telescope.  

Adjust Guider Field of View
If you removed the guider spacer ring, you must align the prism to 'grab' the most light from the light cone.  This is best done in daylight so that the full field of view reflected by the prism is clearly visible.  Take the camera body off the guider to access the hex set screws on the guider eyepiece holder.  Tape a large cap (Reducer/Corrector works) over the T-Adapter to block off stray light.  Place a low-power eyepiece -- 20-mm or 15-mm with the Reducer/Corrector -- in the holder and focus.  Use the long prism adjustment screw on the front of the eyepiece holder to center the field of view vertically; backing out 6¾ turns from all-the-way in works for me.  Loosen the hex set screws at the base of the eyepiece holder so that the holder/prism can turn freely.  Observing through the eyepiece, turn the holder until the field is centered horizontally.  Now tighten the set screws.  

Working with the Guider
It is handy to understand the placement of the guider field-of-view (FOV) in relation to that of the camera viewfinder and finder scope.  Do this in daylight on a distant target. 

With all parts assembled as instructed in the sections above, the view through the camera may show a small bump along the bottom of the frame.  This is caused by the guider prism.  The guider field is centered horizontally on this bump and is vertically centered some distance below it.  The Reducer/Corrector and a 20-mm guiding eyepiece will have a FOV that extends ¼ into the camera frame and ¾ below it.  Only the tip of the guider FOV will be in the camera frame without the Reducer/Corrector.  

When setting the prism adjustment screw to find a guide star, the last turn should be "inward," or clockwise if you were facing the screw from the screw head.

View a target though the guider eyepiece and then look through the telescope finder.  A standard straight-through finder will show the target to be some distance above the cross-hair -- perhaps ¼ the way from center to the edge.  Note this position so you can use it to place a guide star in the field of the guider.

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Photography Counterweight (C5/C5+)

Used when piggybacking a camera.  Setup weight to be unbalance slightly toward east so that RA drive has something to work against.

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Telescope Maintenance

Cleaning Fluid for External Optics (All Models)

The advantage of mixing your own fluid is that commercial lens cleaning fluid streaks, because it contains detergent.  Use a mixture of 6 parts isopropyl alcohol to 4 parts distilled water.  If you are starting out with less than 100% isopropyl consult the following table:

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Corrector Plate Removal (All Models?)

If your telescope is very dirty on the inside, it is best to contact Celestron International and arrange an overhaul. But for *accomplished* optical do-it-yourselfer, a corrector plate removal procedure was outlined in the manual for the original Orange Tube C5/C8 of the early 1970s. The company dropped these instructions from later user manuals -- probably do to the exacting nature of the procedure. It's just a guess that the procedure is accurate on follow-up models of the 5" SCT. Details and cautions on obtaining these instructions can be found at: SCT Corrector Removal and the "Orange Tube".

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Base Maintenance (C5/C5+)

Place the base on a steady table without the telescope and proceed as follows:

• Check base fork-arm by wiggling it.  If loose: tighten the two 3/16” hex bolts at base of fork.  Remove C5+ declination motor, if installed, to reach bolts.

• Pull/push on declination slow motion knob to see if it slides back and forth.  If so, loosen setscrew on knob with allen wrench.  Push knob inward and tighten setscrew.  Repeat with opposite knob or motor gear if optional C5+ declination motor is installed.  Wrench for motor is smaller than that used on DEC knob.

• If C5+ declination motor is installed: view from gear-teeth side to make sure motor gear and declination gears are aligned.  View planar side to make sure teeth mesh with some backlash (space).  Make sure motor is seated tightly by hand screw beneath it.  I use a small shim of wood between the motor and bottom part of the bracket to accomplish this.  Check tightness of the 11-mm clutch hex-nut in front of declination gear.  It is over-tight if turning the declination knob on the other side if difficult.  It is loose if the declination motor can’t turn the gear.  When the motor is operating you should notice the opposite slow-motion declination knob moving.

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Tripod Maintenance (C5/5+ but can apply to all tripod mounted scopes) 

With the wedge off, spread the tripod legs on firm ground or flooring:

• Shake tripod head to see if leg bolts rattle where they attach to the head.  Tighten if needed, but make sure legs extend and collapse smoothly.  Slightly loosen bolts if legs are hard to extend.  Field Tripod #93591 has ½” or 13mm bolt heads.

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Diagonal Testing (All Models) 

Perform this optical test by placing the scope on mount or firm tripod. 

• Install the diagonal so the eyepiece holder is horizontal with the ground.  Place a cross hair or high-power eyepiece in place.  Center the field-of-view on a distant object if daylight or Polaris at night.  Loosen screws that hold diagonal to visual back, hold diagonal from falling out and swing it around 180-degrees.  Tighten screws to secure the diagonal and view the object again.  If the object has left the center of field your diagonal is misaligned.  You’ll have to examine it to see if adjustments are possible.

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Declination Setting Circle Care (All models so equipped)

Angular Accuracy Test

The scope does not have to be mated to the equipment to do this. 

• Place a piece of masking tape on the (stationary) side of the circle opposite the index mark. 
• Set the circle to zero-degrees on the index mark. 
• Put a pencil mark on the tape at the zero-degree mark opposite this. You now have a secondary index mark. 
• Move the declination axis in 45-degree increments with respect to the main index. 
• At each point, note the reading on the secondary (pencil mark) index. 

If the numbers always match to within a hair: you're fine. If not: your circle is not centered (for disks) or has inconsistent gradient mark spacing (for rings). There is probably no way to fix bad circles short of replacing them; you'll have to take any error into account when trying to locate objects with your declination circle.

Calibrate Declination Circle

Your circle must pass the angular accuracy test above for this procedure to be accurate. This test works best on a distant land target. 

• Point telescope at a distance object and note the DEC circle reading. 
• Rotate the telescope 180-degrees (12-hours) in RA and adjust the DEC axis to re-center the target. 
• A difference between declination readings indicates misalignment of the circle: loosen the DEC circle hardware, and rotate the circle it to split the difference between the two readings. Tighten the hardware. 
• Redo the test to confirm the fix.

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