What to Do If Everything Is Not the Way it Ought To Be

If a star test or planetary image seems to reveal subpar optics, what should you do? If you are a beginner, get a second opinion from an experienced SCT-using a fellow amateur from the astronomy club or an Internet group. Couple factors such as col-limation, cooldown, and seeing with the anxious feelings that come when testing a new and expensive telescope, and it is all too likely you will condemn an excellent SCT. As a novice, you really do not have a good idea what star test or planetary images should look like under a given set of conditions. Get help.

If all the checking and consulting in the world still shows the optics to be punk, get on the telephone. If the CAT is new, call the dealer; if you have had it for a while, call the manufacturer. When you speak to either, describe exactly what you have seen. The good thing is that both Meade and Celestron have excellent records of correcting optical problems. Just be sure you know what you are talking about.

Chapter 8 is the "why you came here in the first place" one: a tour of the night sky's wonders with your CAT.

Quick CAT Troubleshooting Guide


Probable Cause

Corrective Action

Computer/Go-to/Electrical Problems

Telescope is dead. Hand control No power to system. Batteries low or display is blank, and power-on dead, no AC power to AC adapter, light is not illuminated. faulty AC adapter, cords or connections faulty, fuse(s) blown.

Double-check that telescope/mount power switch is on. Test batteries under load using battery tester (not just a multimeter). If the scope is normally powered by batteries, if possible, switch to AC power. If an AC power source is not available, try a different DC source (12-volt DC battery or internal cells). If the scope is normally run on AC, switch to a DC power source. Check power cords for continuity. Ensure all connections are secure (at both telescope and battery/AC adapter ends). Replace batteries and repair/replace cords as necessary. Check status of fuses inside telescope drive base if present (refer to manual for location/presence) or in the DC line cord (typically, there is a small fuse in the tip of DC "cigarette lighter adapters" that is revealed by unscrewing the tip). If the scope fails to power up after these checks, CONTACT MANUFACTURER.

Abnormal electronic indications at power up, especially garbled hand control display or unresponsive hand control.

Connectors or cables faulty, low power, poor power quality. Computer/firmware problems.

Check battery and battery cable. If the battery is low, recharge. If on AC power, switch to DC. Small AC power supplies produce poorly filtered DC that can cause computer problems. Check/clean hand control RJ style ("telephone") connectors. During cold weather (below freezing, especially), battery performance will decrease. Keep the battery warm, at least prior to beginning observing, or operate from an AC power supply. Check/replace hand control connecting cable. Perform a "reset" ("factory defaults" for Celestron NexStar telescopes) of the hand controller to resolve program/firmware problems. If no improvement is noted, try reloading hand control firmware. If the telescope is a Celestron NexStar, try reloading motor control firmware as well. If problems persist, CONTACT MANUFACTURER.

Hand controller stops responding to all commands. Display is frozen.

Program problem. Cable problem. Defective hand controller.

Power scope off, wait 90 seconds, and power scope back on. If problem clears initially but returns, check HC cable. Try a hand controller software reload. If the hand controller is still frozen after power up, it may still be possible to reload Meade Autostar firmware via their "safe load" procedure (see manual). If power cycling, a software reload, or a cable check fail, CONTACT MANUFACTURER.

Probable Cause

Corrective Action

Go-to alignment failure.

During alignment, the telescope always stops its alignment slew a great distance (more than 10) from target stars.

Telescope misses go-to targets despite successful alignment.

Wrong go-to alignment stars were centered. Poor SkyAlign alignment objects chosen. Telescope was not placed in home position properly. Incorrect setup information entered in hand control. Electronic compass or level sensor failure. Circuit board failure. Motor failure or problems.

Incorrectly set time, time zone, date, latitude, or longitude. Poorly leveled alt-azimuth mode telescope. Poorly polar aligned equatorial mode telescope. If the telescope points north during alignment or is pointed north to place it in Home Position, magnetic variation or improper setting of Home Position. Poor centering of alignment stars, backlash, normal accuracy variations due to telescope mechanical characteristics. Poor polar alignment with some equatorial mode telescopes.

Use a star chart or planisphere to help ensure correct alignment stars were centered. If stars selected by the telescope were unfamiliar, try alignment again, selecting known stars as alternatives (correct stars will always be the brightest stars in the area where the scope stops). Follow manufacturer guidelines for choosing alignment stars carefully if the telescope does not normally pick them ("Celestron" SkyAlign procedure). Try an alternate alignment method: for instance, Two Star instead of "SkyAlign". If the telescope does not center alignment stars in the eyepiece or finder, do not stop or accept them; center them using the hand control direction buttons. Check manual and online sources for home position setting information. If home position requires pointing scope north and level, use Polaris rather than a compass as a north reference. Level the telescope using a carpenter's bubble level. Check settings in hand control and especially proper "scope type/model" entry. If alignment continues to fail, CONTACT MANUFACTURER. Review hand control entries for correct time, time zone, date, and position entry. The user is required to set time zone and Daylight Savings Time (DST) status (on/ off), even with GPS telescopes. Double-check for correct DST state. If the telescope uses an electronic compass for north-pointing, check the manual for a compass calibration (sometimes referred to as "calibrate sensors") routine to correct for magnetic variation. Use Polaris as a north reference when setting Home Position. Use a polar borescope or other aid for polar alignment of an equatorial mode telescope.

Use a medium-power (100-150x) crosshair reticle eyepiece for centering go-to alignment stars. Center alignment stars using only up/right or down/left keys as instructed (Celestron). Perform Calibrate Motors and Train Drives routines as outlined in manual (Meade). If objects are accurately placed on one side of the sky and are off on another, switch to a lower-power eyepiece for object finding or use "sync" or "precise go-to" as appropriate. Some GEM and equatorial mode fork-mount telescopes require good polar alignment for best go-to performance. Use a polar alignment aid such as a polar borescope or polar alignment reticle on a finder or a drift alignment (see the astro-imaging chapter) to improve polar alignment accuracy.

Telescope begins slewing uncon- Low battery, poor-quality AC power, trollably during observing. cable problems. Circuit board failure.

Telescope motors stall. Unbalanced load. Low battery power due to cold weather. Circuit board problems.

Motors do not move telescope tube when hand control buttons are pressed. Telescope appears to have powered up normally.

Hand control display dims and becomes difficult to read, or displayed messages scroll too slowly Telescope GPS receiver never gets a position fix (finds site latitude and longitude) or takes a long time (more than 30 minutes) to pick up satellites.

Slewing (moving) speed too slow. Altitude-azimuth/RA declination locks not firmly engaged. Slew limit "filters" in the hand control that prevent the telescope from moving below the horizon or bumping into a tripod leg during slews are incorrectly set. Circuit board problems. If only one axis is affected, defective motor or declination cable. Cold weather dims and slows LCD displays.

Obstructed view of GPS satellites. Failure of receiver to retain almanac data. Faulty GPS receiver.

Switch to a DC power source if on AC; use an alternate DC source or switch to AC Z!

if on battery. Check power cable and connections. Check declination cable if the ¡»

mount has one. Cycle power to scope (turn scope off and back on), leaving power i—

off for at least 90 seconds. Reset hand control. CONTACT MANUFACTURER. <gl

Ensure the telescope is balanced in RA/declination and altitude/azimuth, adding bal- ^ ance weights to fork-mount telescopes as required. Meade scopes may need to have the "calibrate motors" procedure performed per the manual, especially if the power 3-

source has been changed (including the installation of new internal batteries). When Q

temperatures are below freezing, battery power output drops, sometimes enough to ft cause erratic telescope operation and motor stalling. Use AC power or keep battery ¿H

warm prior to beginning an observing run. CONTACT MANUFACTURER. Follow the instructions in telescope instruction manual to see how to increase slewing speed with hand control. Lock locks on both axes securely. Check "slew limit" settings in the hand control for proper settings. Check declination cable if present. CONTACT MANUFACTURER.

Keep hand control by keeping it in a pocket or attaching a small heat source.

If the telescope/mount never gets a fix, check for a clear view of the sky; especially the celestial equator and southern horizon. If the GPS receiver is an optional add-on module, ensure GPS is turned "on" in the hand control. For a telescope that consistently takes longer than 30 minutes to get a fix, check GPS receiver for the presence of a battery. Some Celestron SCTs use a small rechargeable battery to hold almanac data in memory (see http://www.nexstarsite.com). In some cases this battery can become discharged if the telescope has not been used in a considerable length __

of time, but can be recharged by leaving telescope plugged in and powered on for 48 hours. If GPS remains problematical, CONTACT MANUFACTURER. ^


Probable Cause

Corrective Action

Objects are difficult to center in the eyepiece using hand control direction buttons.

Fuses in the telescope drive base or DC line cord blow repeatedly.

Telescope does not communicate with an external laptop computer connected to its serial port. Or communications are intermittent. Or telescope demonstrates erratic behavior (uncontrolled or improper slewing) when connected to a laptop or other PC. Telescope is very loud during highspeed slewing.

Optical Problems

Images of stars, planets, and other objects are not sharp and clear. Images cannot be properly focused. Planetary detail is lacking.

Slewing speed set too high. Backlash (telescope does not begin moving immediately when a button is pressed).

Mechanical problems causing motor stalling. Electronics failure. Short in power cord/connector.

Faulty serial cable or connectors. Improper communications setup. Computer serial port problem. Electronics problem.

Most go-to telescope motors are noisy when slewing at maximum speed. Motor gear problems.

Poor seeing conditions indicated by an image that "boils," wavers, or moves around in the field of view, especially at high magnifications. The object being observed is too close to the horizon. Poor seeing caused by local terrain.

Follow instructions in the manual to reduce slewing speed of hand controller. Also check the instructions for procedures for reducing backlash.

Test for possible mechanical binding of the mount by unlocking its locks and moving the telescope by hand in altitude/azimuth or Right ascension /declination. Check for damaged power cords and connectors. Verify that replaced fuses are seated securely in their holders. CONTACT MANUFACTURER.

Ensure proper style of serial cable is in use (i.e., Celestron for Celestron telescopes, Meade for Meade telescopes). Check serial cable with a multimeter. Inspect serial receptacle (usually on the hand controller). Be sure proper serial (com) port is identified in the program on the PC used to control the telescope. If the computer is using a USB-serial adapter cable, try a different brand of USB-serial adapter or a PCMCIA serial card. Double-check all settings in the PC software (including communications parameters, telescope type, and site latitude and longitude) and in the ASCOM utility if the program uses that to communicate with the telescope. High-noise levels are normal for many telescopes/mounts during go-to slews. If the sound threatens to wake the neighbors, speed during go-tos can be reduced for some telescopes, resulting in less noise. See the instruction manual. If motor noise has increased markedly recently, CONTACT MANUFACTURER.

Wait until seeing conditions improve. Conduct critical observing only when target objects are at least 30 degrees above the horizon. Avoid observing objects "over" heat-radiating roofs, paved parking lots, etc.

Images are poor early in the evening, but improve as the night wears on.

Tube currents and mirror figure problems caused by a telescope that has not been allowed to adjust, or "equilibrate," to outdoor temperatures.

Telescope not focused.

Objects are blurry and indistinct. Stars resemble donuts with dark centers.

Planets lack detail and stars, even those near the center of the field, are oblong, resembling comets rather than symmetrical points. Objects are blurred, surrounded by haloes, and dimmer than normal. Stars at the edge of field are out of focus. When they are focused sharply, stars in the center are out of focus.

Stars toward eyepiece field edge are badly misshapen and look more like seagulls or footballs than stars. "Footballs" change orientation on either side of focus (astigmatism).

The telescope is out of collimation.

Telescope optics extremely dirty.

Curved SCT field of view or poor-quality eyepiece.

Eyepieces are of poor quality and exhibit astigmatism or other optical aberrations. Astigmatism in user eyes cause Astigmatism in telescope.

Allow the telescope to cool sufficiently. If the temperature differential between inside ¡i and outside is small, 30 minutes is adequate cool-down time. If, however, the Ei temperature difference is large or critical or high-resolution observing or imaging is to be attempted, at least 2 hours should be allowed. A rear port cooling fan, either ^

home built or purchased (Appendix 1) can speed cooldown. <

Adjust the focus until the image is sharp. Turn the control in the direction that makes 3"

stars and planets "smaller" or increases the sharpness and contrast of lunar details. O

Continue turning through best focus until the image begins to defocus again, and then Q

turn in the opposite direction to bring the image back to maximum clarity. If the tele- -1

scope is initially greatly out of focus, all but the brightest objects may be invisible. In that case, point the telescope at a bright star, planet, or a distant terrestrial object such as a streetlight, and turn the CAT's focus knob until the target begins to get smaller/brighter. If no improvement or the image gets worse, turn the control in the opposite direction. Perform rough and fine collimation using the procedures outlined in Chapter 9.

Follow the optical cleaning instructions in Chapter 9. Optics dirty enough to cause performance degradation will be immediately obvious.

The SCT's curved focal plane will distort stars at the edge of the field. An f/6.3 reducer corrector or a higher quality eyepiece will improve their appearance.

Use higher-quality oculars if the edge-of-field appearance is important. If astigmatism appears to be the problem (see the star test section in this chapter), ensure it is not in the observer's eyes. If astigmatism elongation "tracks" as the observer's head is rotated about the eyepiece, the problem is in the eye. If the astigmatism moves as the eyepiece is rotated in the diagonal, the problem is in the eyepiece. If neither, the astigmatism is in the telescope itself. CONTACT MANUFACTURER.


Probable Cause

Corrective Action

Few details visible on the Moon and planets at higher powers (150x and above).

Stars and planets were initially clear and sharp, but begin to display halos later in the evening.

Objects lack clarity when observed from indoors through a window.

Planetary or deep sky images are sharp until a filter is placed on the eyepiece.

Telescope was precisely collimated in straight-through fashion (eyepiece inserted directly in visual back), but collimation appears off when a star diagonal is used. Optics are free of dew and dirt, but bright stars display halos.

Magnification is too high for telescope aperture or current seeing conditions.

Optical elements (corrector plate or eyepiece) have become covered with dew.

Aberrations introduced by observing through window glass. Seeing problems caused by an open window.

Defective or poorly made eyepiece filter. Failure to refocus following attachment of filter. Defective star diagonal. A poorly constructed or defective star diagonal can affect telescope alignment.

Tree limbs or other obstructions are blocking the telescope's view of an object. This will appear at first as a halo, a diffuse ring of light around the object, and will cause a loss of detail. Defocusing the image by a large amount will reveal obstructing objects by their outlines against a defocused bright star or planet.

Reduce magnification. "Maximum" usable magnification for a given telescope is about 60x per inch of aperture (480x for an 8-inch telescope). Poor seeing conditions, not enough telescope cooldown time, or an inexperienced observer, will limit maximum usable magnification to much less.

Use dew removal/prevention tools including a dew shield, dew zapper gun, and dew heater strips. Early dew buildup will be subtle. The first indication is that bright objects will develop halos of scattered light. As more dew collects on the corrector, detail will be lost.

Modern plate glass is surprisingly flat, but some aberrations will be introduced. Opening a window causes air from inside the house to flow out, creating turbulence and ruining seeing. Under normal circumstances, do not attempt to observe through an open or a shut window.

Replace the filter with a better-made one. Most filters will require refocusing of the telescope after they are added to an eyepiece.

Either replace the star diagonal with a better-quality unit or collimate with the diagonal in place. If the diagonal is very poor, collimation will only be good for the rotational position the diagonal was in when the telescope was collimated.

Move the telescope or change its aim until its view is clear of obstructions.

Moon or planet limbs ¡edges) are rimmed with red and blue light.

Differential refraction. Eyepiece aberration.

Focus control action is stiff or rough.

Images move across the eyepiece field of view when the focus control is turned.

Focus control alignment or bearing problems.

Focus shift caused by the moving-mirror-focusing system of SCTs.

Images of all objects poor despite Telescope optics defective.

good collimation, adequate cooldown, clear and transparent skies, and stable atmospheric or local seeing.

Mount/Mechanical Problems

Tracking is poor. Objects drift out Poor polar alignment for GEM or of eyepiece field in only a few wedge-mounted fork telescopes. Poor minutes. go-to alignment for alt-azimuth mode fork-mounted scopes. Images "shake" and vibrate when Too light or improperly assembled tel-the telescope or focus control is escope mounting. High magnification. touched, even at low-medium Windy conditions. Unbalanced OTA. magnifications.

Differential refraction caused by thick air near the horizon will give one limb of a ¡i planet or the Moon a red-colored border and the opposite limb a blue border. This Ei is f /Of caused by chromatic aberration in eyepieces or the main optics. This effect can also be caused by tube currents in an uncooled telescope. Do not attempt to ^

observe when the Moon or a planet is less than 30 degrees above the horizon. <

Allow telescope sufficient cooldown time. If the effect continues, replace eyepiece 3-

with a higher quality model. Q

Try moving focus to both ends of travel (do not force anything; if knob does not turn Q

easily, stop). If action does not improve, CONTACT MANUFACTURER. -I

About 30 to 45 arc seconds of focus shift are normal in mass-produced SCTs. If the shift is excessive, try moving the mirror to both ends of its travel using the focus control. That will help redistribute grease on the baffle tube. If focus shift is still "excessive", CONTACT MANUFACTURER.

If defective optics are suspected, perform the star test. If possible, get a "second opinion" from an experienced SCT user. If results indicate faulty optics, CONTACT MANUFACTURER.

Improve polar alignment accuracy by using polar alignment aids such as polar alignment borescopes (GEM mounts) and finders with polar alignment reticles (forks). Perform a drift alignment (see astro-imaging chapter). Improve on go-to alignment by precise star centering using a reticle eyepiece. Ensure all tripod (and wedge if one is in use) hardware —bolts, nuts, etc. —is sufficiently tight. Tripod spreader should be firm against tripod legs but not so tight it will cause damage. Learn to exercise a "light touch" when focusing or purchase a remote-control electric focus motor. If telescope tripod legs are equipped with both rubber "crutch tips" and spikes, remove the rubber tips to reveal the spikes. Purchase shock isolation "vibration suppression" pads (sold by Celestron, Meade, and Orion) for use under telescope leg tips. An unbalanced condition of the


Probable Cause

Corrective Action

A fork-mount telescope is overly prone to vibration (vibrates for more than 5 seconds) when the telescope is set up on a wedge for equatorial mode tracking. High-power images vibrate continuously even when telescope is not being touched. During long-exposure astrophotog-raphy, star images trail; they are lines or ovals rather than points.

Telescope mount movement is very stiff in cold weather. The telescope can be moved a small amount in RA/declination or altitude/azimuth when mount locks are engaged. Tripod leg extensions slip.

Wedge too light for telescope. Wedge hardware is loose.

A stepper motor drive is causing vibration as it moves in discrete "steps" as the telescope tracks. Poor polar alignment. Periodic error causes star trailing when not "guided out."

Grease used to lubricate the mount is overly viscous at low temperature. Improper gear mesh.

Weak or damaged leg extension locks.

CAT's OTA (tube) will add to vibration problems. Balance the telescope using optional balance weight systems if necessary. GEMs can be adequately balanced by moving the counterweight along its shaft (an additional counterweight may have to be purchased in some cases) or the telescope along its mounting rail. Wedge may need to be replaced with a heavier duty model. Check that all bolts; especially those loosened to adjust wedge in altitude, are tight.

This usually is due to maladjustment or misalignment of gears and or RA drive motor CONTACT MANUFACTURER.

See instructions in the imaging chapter for performing an accurate drift polar alignment. Guide out errors either manually with a crosshair eyepiece and a guide scope or automatically using a guide camera. If the telescope mount features periodic error correction (PEC), make a "PEC" recording to reduce periodic error. CONTACT MANUFACTURER.

A small amount (Vi-inch or less) of "play" is normal. If the gears are tightly meshed enough to eliminate all slop, they will usually bind and stall the mount motors at some point in their rotation. If play is excessive, CONTACT MANUFACTURER.

Do not over-tighten leg locks, which will cause damage and prevent them from being adequately secured. Never extend tripod legs if they cannot be locked firmly. CONTACT MANUFACTURER.

Bolts, nuts, and other hardware on Low-grade stainless steel hardware mount and OTA begin to rust. was used on mount and OTA.

Some bolts, nuts, and fasteners can easily be replaced with higher-grade stainless steel hardware. Be cautious about removing and replacing hardware on OTA. If in doubt, CONTACT MANUFACTURER.

AC alternating current, CAT catadioptric telescope, DC direct current, GEM German equatorial mount, GPS global positioning system, ¿CD liquid crystal digital, OTA optical tube assembly, PC personal computer, PCMCIA Personal Computer Memory Card International Association, RA right ascension, SCT Schmidt Cassegrain telescope, USB universal serial bus a ft >


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