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.


Revision color key:
* -- June 11, 2005
* -- Sept. 22, 2002 

"Orange Tube" note:
These telescopes are the original C5 (1971 to 1985) that came mounted on two-tined forks -- like a "mini" C8. They are not all orange: some later models were black.

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+)

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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.

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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!

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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+):

Alignment Using Drift Method

This should be done after rough polar alignment. 

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

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)

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Align the Internal Optics (All Models)

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

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General Usage Notes

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

RA slow motion

Declination slow motion

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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.

Motor Drive Features
Southern Hemisphere reversal With power to the drive base off, hold down the North/South buttons on the hand controller and turn the base on. After a few seconds release the buttons. Set the RA circle to an index point on the outer rim of the dial. Lock the RA axis. If the RA circle gradually moves counter-clockwise, you are now setup for Southern Hemisphere operation. You can ignore any instructions in the manual to switch drive-motor wires around. Just turn the drive off and on (without holding the buttons) to return to normal mode.
North/South Button reversal You need the optional declination drive installed to test this. With power on, note the direction the declination motor gear turns when holding the South button on the controller. Now power-down the drive base, hold down the South button on the hand controller, and turn on the base. Release the button after a few seconds. Recheck the rotation of the declination motor gear now. If it moves in a contrary direction, your chip has the North/South button reversal feature. Cancel the reversal by powering off and on -- without holding the button.
High-Speed Tracking mode With power on, see if you can increase the speed in RA or DEC (if equipped with optional motor) by holding down the desired direction button and then pressing the opposite button -- so both buttons are depressed. There should be a noticeable change in motor noise if this feature is implemented.

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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.

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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)

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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:

Isop Purity Parts Isop Parts Water
60 100 0
70 86 14
80 75 25
90 67 33
91 66 34
100 60 40

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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:

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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:

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Diagonal Testing (All Models) 

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

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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. 

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. 

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