Knowledge Base

  • Self-Guiding

    No telescope drive system is perfect. All have small flaws in their drive gears
    that cause the telescope to speed up or slow down periodically. These drive train
    errors (and gradual declination drift from not being precisely aligned on the celestial
    pole), can cause the stars in long exposure photographs to develop small tails or
    elongate unnaturally. For the sharpest long exposure photos, the telescope should
    be guided during the exposure, speeding up or slowing down the drive to compensate
    for the unavoidable unwanted telescope motions as they happen.

    Many SBIG CCD cameras are self-guiding, making the telescope's right ascension drive
    and declination drift error corrections automatically during the course of a long
    exposure. This means that you don't have to stay glued to a crosshair guiding eyepiece
    during the entire exposure to correct for those errors manually. You can even leave
    the telescope entirely, letting it guide and take its photographs automatically.

    The self-guiding SBIG cameras use two CCD detectors, one is a Kodak 657 x 495 pixel
    TC-237H detector for guiding, while the other is a larger detector for collecting
    the image. The detectors are mounted in close proximity to each other within a single
    camera body. Both are focused at the same image plane. This patented guiding method
    allows you to focus both taking and guiding detectors simultaneously.

    Some competitive cameras have a separate guiding detector that mounts in an off-axis
    guider body. This two-housing system requires more setup time to focus each detector
    independently than does the one-time focus of the SBIG cameras. Still other cameras
    have one detector, but use a portion of that detector to guide while the balance
    of the detector collects the image. By using a completely separate internal CCD
    for guiding, the SBIG cameras allow 100% of the imaging CCD to be used to collect
    the image, an improvement over other single chip designs.

    In SBIG tests performed under moderate light pollution with an 8" f/6.3 telescope,
    randomly pointing the telescope with a self-guiding SBIG camera in it toward objects
    in relatively star-poor areas of the sky away from the Milky Way resulted in stars
    on the guiding detector being bright enough to be used for guiding 95% of the time.
    TheSky
    software from Software Bisque (supplied with each camera) can print finder charts
    showing the correct placement of the guiding detector's field of view relative to
    the imaging CCD's field of view. Using this software tool to plan your nights imaging
    will help you orient the camera for proper guide star acquisition in those few cases
    where a bright-enough guide star might not be immediately apparent.

  • TDI

    TDI (Time Delay Integration) imaging lets you image large areas of the sky without guiding - so that any telescope will do. In TDI, you point the camera at an area of the sky and turn off the telescope drive. This lets the stars drift across the field of view. The imaging detector is clocked (read out) one column of pixels at a time in sync with the rate of stellar drift. This keeps the accumulating charge underneath each star's image until the star reaches the edge of the CCD, and the readout register, at which point the signal is sent to your computer for storage and later processing. The resulting image has an exposure time equal to the amount of time it takes the stars to drift across the CCD.

    Depending on the focal length of the telescope, this can be many minutes. Because the scope itself is not moving, there is no periodic error and no guiding error during the exposure! Furthermore, the image you are recording scrolls as the sky moves past, so the image file can be as many pixels tall as your CCD imaging detector is tall by 1000 pixels in width, or 2000 pixels wide, or 3000, etc.

    An SBIG user, Christoph Flohr, has written a very capable program for doing this kind of imaging with SBIG cameras, particularly the ST-7/8/9/10 series. The program can be downloaded for free from www.driftscan.com. For a more complete SBIG .pdf file describing the TDI process, click on this link.

  • Indicator Lights

    A set of five LED indicator lights on the side panel of the camera lets you know if your input voltage at the camera is getting too low for normal operation. A green LED lets you know the camera is booting up and gives camera exposure status during normal operation. A red LED provides a warning if the heat sink gets too hot. This could happen, for instance, if you were running high power to the cooler and the fan failed for some reason. In this case the camera automatically reduces power to the two-stage cooler to prevent damage. An amber LED warns of an input voltage drop to 11 volts or less but the camera will continue functioning normally. A second amber LED warns of an input voltage drop to 10 volts but the camera will still continue functioning normally. The last red LED warns of an input voltage drop to 9 volts or less. In this case, the camera automatically turns off the TE cooler and continues to operate normally without cooling until the voltage drops to the point that the camera shuts down (below 7 volts).

  • Advanced Series mount review

    A review of the Celestron heavy duty CG-5A Advanced Series computerized German equatorial mount in Sky & Telescope magazine said, "When the mount was fitted with a short-tube 90-millimeter refractor, vibrations damped out in just 1 to 1½ seconds after I gave a sharp rap to the tube. When I placed vibration-suppression pads (a Celestron option) under each leg, the damping time was cut in half. This is performance as good as by any mount I've seen at any price."

    The Sky & Tel review added, "The Advanced Series CG-5 mount is an ideal platform for a 3- to 5-inch refractor, a 4- to 6-inch Newtonian reflector or Maksutov-Cassegrain, or a 5- to 9¼-inch Schmidt-Cassegrain. The smaller, shorter, and lighter the optical tube assembly, the sturdier the combination will be. When mated to a 4-inch short focus refractor or a compact 5-inch Maksutov or Schmidt-Cassegrain, the Advanced Series mount forms an amazingly solid platform that is virtually insensitive to vibration. Yet the complete package is light enough to be carried outside fully assembled."

    It should be noted that periodic drive speed errors are a problem with all worm gear telescope drives, no matter what size the telescope or what its cost. Due to the relatively small size of the drive gears in the Advanced Series mount, periodic error may be noticeable during long exposure astrophotography in the form of stars that look like short streaks in your images, rather than points of light. Since automatic periodic error correction is not available in the Advanced Series mount, long exposure astrophotography will require careful manual guiding if it is to be successful. Lunar and planetary exposures are all very short, so guiding is not required during this type of photography. Visual observing is not affected by periodic drive errors.

    Because of the possibility of periodic drive errors during long exposure imaging, the Sky & Telescope review cautioned that, "The Advanced Series' strength is serving as a mount for a telescope used visually and for snapshots or webcam imaging of the Moon and planets."

    Despite the long exposure imaging caution, Sky & Tel concluded that "for an affordable customized telescope with Go To capability the Celestron Advanced Series mount is a great choice."

  • NexStar Computer details

    The NexStar computer hand control has a built-in database of more than 40,000 stars, deep space objects, and solar system objects it can locate for you. The computer's memory contains the following objects:

    • the entire RNGC (Revised New General Catalog) of 7840 nebulas, galaxies, and star clusters

    • the IC (Index Catalog) of 5386 nebulas, galaxies, and star clusters

    • the Messier Catalog of the 110 best known deep sky objects

    • the Caldwell Catalog of 109 fascinating objects that Messier missed

    • 20 famous asterisms

    • the Abell Catalog of 2712 galaxy clusters

    • 25 selected CCD imaging objects

    • 29,500 selected SAO stars, including variable stars and multiple star systems.

    Also included are the eight major planets out to Pluto, as well as the Moon, for a total database more than 40,000 stars and objects. It's enough fascinating objects to keep you busy observing for the rest of your life.

    You can also store and edit the right ascension and declination of 100 objects of your own choosing, such as the comet and asteroid coordinates published monthly in Astronomy and Sky & Telescope magazines. The computer control can quickly find any of those objects at your command, and track them with high accuracy for visual observing or casual astrophotography.

    A review in Sky & Telescope magazine commented, "To quantify the Go To pointing accuracy, I spent several nights slewing to 50 objects selected from the NexStar's database. About one-third of them ended up dead center in the field, another third landed within ½° of the center, and the remaining third were within 1° of the center."

    All of the database and scope operation information is displayed on a double line, 16-character, liquid crystal display on the hand control. This display leads you through the steps necessary to line up the scope on the sky, locate objects, control scope functions like the brightness of the hand control display, and much more. It shows you basic information about the object being viewed (such as the object's name, catalog designation, type, magnitude, and so forth). In addition to this basic information, there is enhanced information on over 200 of the most note-worthy objects. The display also shows you the right ascension and declination coordinates at which the scope is currently aimed.

    The Sky & Telescope review said, "After using several NexStar-equipped telescopes in recent years, I can attest to the quality of the software and hardware for Celestron's Go To system. The package is reliable and offers quick access to an excellent array of databases. I especially like Celestron's Tour mode, which steps a user through an eclectic choice of deep-sky objects, quirky asterisms, and fine double stars, the latter being a class of objects great for urban observing that many Go To systems ignore. Using NexStar scopes, I've been introduced to many fine double stars."

    There are 19 fiber optic backlit LED buttons that glow a soft red in the dark to make it easy for you to control the computer without affecting your dark-adapted vision. An RS-232 communication port on the hand control allows you to operate the telescope via a personal computer using optional NexRemote telescope control software. The Sky & Telescope review said, "The author tried Windows and Mac programs, including Desktop Universe, ECU, MegaStar, SkyMap Pro, Starry Night, and TheSky, and all controlled the mount without any problems." You can upgrade the software via the internet from Celestron's website so you can always have the latest version of the NexStar software available to control your scope.

    There is also an Autoguider port that can use a CCD autoguider to automatically control the drive motors during long exposure astrophotography. A high precision pointing subroutine ("precise go-to") in the computer lets you point accurately at objects that you want to photograph that are too dim to be seen though the scope.

    Several different alignment methods are built into the NexStar computer, allowing you to choose a level of computer accuracy in automatically finding objects with which you are comfortable. Both the two star "quick align" procedure and two more accurate three star alignment methods (one computer-guided) are easily accomplished in only a few short minutes. You can be observing in less than 15 minutes after you first take the scope outdoors, including telescope set-up time.

    In addition, the NexStar computer hand control is GPS-compatible (using an optional inexpensive SkySync GPS module) for full GPS (Global Positioning System) satellite accuracy. Adding GPS to the computer is something no competitive scope can do. Once the scope is approximately polar aligned, the 16-channel SkySync GPS system uses signals from government satellites to calculate the scope's location on earth in three dimensions with an accuracy measured in meters. The system also calculates the current time based on the split second accuracy of the GPS time signals.

    After the SkySync quickly completes these calculations and enters the information into the computer control for you automatically, the computer then orients the scope with the sky, slews to a pair of guide stars, asks you to confirm that the stars are in the center of the field (and center them if they're not precisely aligned), and then starts finding and tracking over 40,000 objects for you at your command. With the Advanced Series go-to mount and the SkySync, orienting the scope in time and space on earth and aligning the scope on the sky becomes almost as easy a task as simply turning the scope on.

  • CG-5 mount

    The CG-5 German equatorial mount supplied with this Celestron telescope does not
    come with a motor drive as standard equipment, but its manual worm gear drive slow
    motion controls will let you smoothly track celestial objects for visual observing
    with only an occasional twist of the wrist. If family viewing is planned,
    a motor drive means you don't have to worry about the object being observed drifting
    out of view while changing observers. This is especially handy when observing with
    small children or groups of people (at star parties or scout meetings, for example).
    If astrophotography is in the cards, the #MDCG5D motor drive/drive corrector is
    essential. Snap-on plastic covers keep the drive gears (and the optional motor drives)
    free from small fingers, dust, and debris.

        The standard manual right ascension and declination slow motion controls
    have the appropriate length solid or flexible cables to make it easy to reach the
    controls with your particular length optical tube. Large easy-grip knobs make small
    control adjustments a cinch. To make a casual polar alignment for visual use quick
    and easy, there's a latitude scale and fine adjustment controls in both altitude
    and azimuth. If astrophotography is in your plans, an optional polar finder is available
    to increase the accuracy of your alignment.

        The mount's adjustable height tripod has 2" diameter steel legs, with
    excellent damping characteristics. There's a center leg brace for rigidity. The
    brace is drilled to form a convenient accessory tray that holds both 1.25" and 2"
    eyepieces to keep them up out of the dew-soaked grass. A review in Sky & Telescope
    magazine said, "When the mount was fitted with a short-tube 90-millimeter refractor,
    vibrations damped out in just 1 to 1½ seconds after I gave a sharp rap to the tube.
    When I placed vibration-suppression pads (a Celestron option) under each leg, the
    damping time was cut in half. This is performance as good as by any mount I've seen
    at any price."

        One or more counterweights are supplied, depending of the weight of
    the optical tube. The sliding counterweight(s) are locked in place with a single
    hand-tighten thumbscrew each, making it easy to rebalance the scope if you add heavy
    accessories. The mount is easily capable of handling the scope and any reasonable
    combination of accessories you might want to add. If needed, an optional 11 lb.
    counterweight (#1711) is available to balance very heavy loads. The mount's payload
    capacity is over 35 lbs.

        An adjustable dovetail slide bar allows the optical tube to be quickly
    and precisely balanced fore and aft on the mount, eliminating the need for an extra
    counterweight to balance a camera or other accessories. Setup and takedown times
    are exceptionally fast, as a single large hand-tighten knob holds the optical tube
    in place. A second smaller lock knob prevents the tube from sliding off the mount
    should the hand-tighten knob loosen.

        The review in Sky & Telescope magazine concluded, "The Advanced
    Series CG-5 mount is an ideal platform for a 3- to 5-inch refractor, a 4- to 6-inch
    Newtonian reflector or Maksutov-Cassegrain, or a 5- to 9¼-inch Schmidt-Cassegrain.
    The smaller, shorter, and lighter the optical tube assembly, the sturdier the combination
    will be. When mated to a 4-inch short focus refractor or a compact 5-ince Maksutov
    or Schmidt-Cassegrain, the Advanced Series mount forms an amazingly solid platform
    that is virtually insensitive to vibration. Yet the complete package is light enough
    to be carried outside fully assembled".

  • CG-4 mount

    The CG-4 German equatorial mount supplied with this Celestron telescope does not
    come with a motor drive as standard equipment, but its manual worm gear drive slow
    motion controls will let you smoothly track celestial objects for visual observing
    with only an occasional twist of the wrist. Adding optional
    dual axis motor drive #MDCG4D

    will keep objects centered in the eyepiece continuously. If family viewing is planned,
    a motor drive means you don't have to worry about the object being observed drifting
    out of view while changing observers. This is especially handy when observing with
    small children or groups of people (at star parties or scout meetings, for example).
    If astrophotography is in the cards, the #MDCG4D motor drive/drive corrector is
    essential.

        The mount uses precision ball-bearings in both the right ascension
    and declination axes to assure smooth and hitch-free motion of your scope across
    the skies. Built-in non-powered setting circles are provided to help you find objects
    by using their right ascension (hour) and declination (degree) coordinates as shown
    in a star chart or atlas. The right ascension hour circle is equipped with a vernier
    scale that lets you adjust the telescope position in right ascension to an accuracy
    of one minute.

        The standard manual right ascension and declination slow motion controls
    have easy-grip knobs that make manual tracking and small position adjustments a
    cinch. The extra-large control knobs are positioned so that they fall easily to
    hand when observing, so you don't have to grope blindly for the knobs when you need
    to make adjust the scope's position. To make a casual polar alignment for visual
    use quick and easy, there's a latitude scale and fine adjustment controls in both
    altitude and azimuth. The mount can be used over a latitude range of approximately
    20° to 60°. If astrophotography is in your plans, an optional polar finderis available
    to increase the accuracy of your alignment.

        The mount's adjustable height tripod has 1.75" diameter stainless steel
    legs for strength and rigidity. There's a center leg brace that locks the tripod
    legs firmly in place for excellent vibration-damping. The center brace is drilled
    with several holes that will hold your 1.25" and 2" eyepieces conveniently at hand
    and up and out of the dew-soaked grass. The no-tool locking knobs that adjust the
    height of the tripod are located on the inside of the tripod legs. This keeps them
    from snagging clothing in the dark, a thoughtful touch sure to be appreciated. The
    tripod adjusts over a height range of 33" to 47". As with all tripods, it is at
    its most rigid and stable when at its lowest height.

        Two counterweights are supplied to balance the optical tube. The sliding
    counterweights are locked in place with a single hand-tighten thumbscrew each, making
    it easy to rebalance the scope if you add heavy accessories. The mount is easily
    capable of handling the scope and any reasonable combination of accessories you
    might want to add.

        An adjustable dovetail slide bar allows the optical tube to be quickly
    and precisely balanced fore and aft on the mount, eliminating the need for an extra
    counterweight to balance a camera or other accessories. Setup and takedown times
    are exceptionally fast, as no tools are required to assemble the mount and tripod
    and only a single large hand-tighten knob holds the optical tube in place. A second
    smaller lock knob prevents the tube from sliding off the mount should the hand-tighten
    knob loosen.

        The CG-4 equatorial head weighs 10 lbs (4.5 kg). The 7 lb (3.2 kg)
    and 4 lb (1.8 kg) counterweights total 11 lbs (5 kg). The tripod weighs 12.5 lbs
    (5.7 kg). Total weight of the complete mount set up to receive an optical tube is
    33.5 lbs (15.2 kg).

  • Great Polaris mount, ash tripod

    The Great Polaris DX mount has a payload capacity of 22 pounds. This allows the use of midweight optical tubes, plus photoguide scopes and other equipment for advanced astrophotography. The mount has 144-tooth brass main drive gears in both right ascension and declination. To keep to a minimum the periodic error that affects tracking accuracy in astrophotography, the brass right ascension worm gear is precision machined to better than 1 micron (1/1000mm) tolerances for very precise tracking of celestial motion. The brass declination worm gear is machined to 2/1000mm accuracy precision, more than accurate enough for corrections in declination. All right ascension and declination gears are individually inspected before assembly. The end result is a higher unguided right ascension tracking accuracy for the Great Polaris DX than is possible with any lesser mount. Optional single and dual axis motor drives are available for no-hands tracking and guided astrophotography. Standard equipment covers for the optional motor drives keep dust and debris out of the motors for more trouble-free operation in dusty environments.

    The Great Polaris DX has an aluminum die-cast body that's built to be strong, yet light, to satisfy both stability and ease of portability needs. The complete scope, including standard equipment 8.2 and 4.2 pound counterweights and ash tripod, weighs 42.1 pounds, making transportation and setup easy. Additional counterweights are recommended to balance payloads over 13.2 pounds.

    Standard equipment right ascension and declination setting circles, used to help point the telescope at a celestial object by dialing in its coordinates, are precisely engraved in metal. The right ascension circle is marked in 10 arc minute increments, while the declination circle is marked in two-degree increments. Micrometric manual slow motion control knobs in both axes are supplied for manual tracking and centering of objects.

    The Great Polaris DX has a 6 x 20mm 8-degree field polar finderscope as standard equipment. This finder allows you to align the polar axis of the scope precisely and easily on the north celestial pole, rather than just on Polaris, using the mount's altitude and azimuth fine adjustment mechanisms. Precise polar alignment allows for drift-free observing and more precise guided astrophotography. The polar finderscope comes standard with a battery-operated internal variable brightness illuminator and works in both the northern and southern hemispheres. Properly utilized, the polar finder will allow the Great Polaris DX mount to be aligned on either celestial pole with three arc minute accuracy. For those situations when Polaris is not visible, hidden behind trees or buildings, a built-in latitude scale and optional compass allow the mount to be roughly aligned on the celestial pole for casual observing. The mount is designed to operate in both northern and southern hemispheres at latitudes from 0° (the equator) to 62° (Central Canada, Northern Europe, and all of South America). Twin adjustment handles allow quick and precise setting of the latitude. Twin adjustment knobs let you fine-tune the azimuth, as well.

    The mount's adjustable-height 11 pound ash tripod is stable and rigid. The tripod legs adjust in length to put the top of the tripod between 31" and 42" above ground level, to allow the observer to place the focuser at a convenient observing height for most optical tube lengths or optical tube types. Should the tripod legs not have enough extension, for example in the case of a long focal length refractor optical tube, an optional half pillar is available to fit between mount head and tripod to raise the telescope an additional 9 inches. An accessory tray keeps eyepieces and other accessories close to hand and out of the dew-laden grass. A built-in bubble level in the mount allows the mount to be quickly leveled for more accurate tracking by adjusting the length of the tripod legs independently.

    The mount is equipped with a 1.8" dovetail groove for installing telescope optical tubes. No dovetail plate is supplied to hold the optical tube, as the choice of dovetail plates is dependent on the optical tube to be installed. A variety of optional dovetail plates are available. Setup and takedown times are exceptionally fast, as a single large hand-tighten knob (with a separate safety knob) holds the optical tube and dovetail plate in place.

  • Starbright optics

    Starbright multicoated optics: Starbright multicoatings are standard equipment. Celestron is the only major manufacturer to provide multicoated optics as standard equipment at no extra cost on all their catadioptric telescopes. These Starbright multicoatings include 5-layer vacuum-deposited high reflectivity primary and secondary mirror coatings of aluminum enhanced with titanium dioxide and overcoated with a protective layer of silicon monoxide (quartz) for long life. These multicoatings visibly increase contrast on subtle lunar, planetary, and nebula details when compared with competitive scopes with standard single-layer aluminum mirror coatings. They also give you higher light transmission for brighter deep space images and shorter exposure times during photography. High transmission magnesium fluoride antireflection coatings on both sides of the Schmidt corrector lens assure minimum light loss and high contrast.

    Hand-figured optics: Hand figuring the optical system is a complex optical procedure done on a commercial basis only by Celestron. Four separate optical tests are made on every set of Schmidt-Cassegrain optics, using a double-pass laser autocollimator - an Airy disc inspection, a test for spherical aberration by examining the diffraction images on both sides of focus, a Ronchi grating test, and a knife edge test. A skilled optician evaluates these tests, and then fabricates a precision pitch lap and delicately hand polishes the secondary mirror to smooth the optical figure and reduce any small residual zonal defects to vanishingly small levels. Done a few strokes at a time, and testing constantly to evaluate their effect, this final hand-figuring can take hours. But, when it is finished, the optical performance makes every tedious hour of handcrafting well worth the effort.

  • 6" Starbright XLT multicoatings

    The Starbright XLT advanced optical multicoatings package includes mirror coatings consisting of multiple layers of vacuum-deposited high reflectivity aluminum on both the primary and secondary mirrors. The mirror coatings are enhanced with titanium dioxide for maximum reflectivity and then overcoated with a protective layer of silicon monoxide (quartz) for long life.

    A unique combination of magnesium fluoride and hafnium dioxide high transmission antireflection coatings is vacuum-deposited on both sides of the Schmidt corrector lens for maximum light throughput and contrast. The corrector lens itself is made of high transmission water white float glass instead of the conventional soda lime glass (which has 3.5% lower transmission) used in other telescopes.

    The Starbright XLT multicoatings give you higher light transmission for brighter deep space images and shorter exposure times during CCD and DSLR photography. Across the total visual/photographic spectrum from 400nm to 750nm, independent laboratory tests show the new Starbright XLT coatings are 16% brighter overall than even the original industry-standard Starbright multicoatings. They also visibly increase the contrast on subtle lunar, planetary, and nebula details when compared with a scope with standard multicoatings.

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