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Celestron Celestar 8 Deluxe Schmidt-Cassegrain Telescope

Celestar 8 Deluxe Schmidt-Cassegrain
Telescope The original Celestar 8 telescope is a very light weight and economical 8" Schmidt-Cassegrain telescope (SCT) that has become a great success for Celestron, and for that telescopes' purchasers. And then in March 1997 Celestron responded to requests from consumers who desired a more sophisticated 8" SCT, better suited to astrophotography and CCD imaging. The result is the "Celestar 8 Deluxe".

Company Seven generally recommends that adults interested in astronomy acquire nothing less than an 8 inch aperture in a mirror telescope design. The Celestron 8 provides a good value for astronomy. With more than 635 times the effective light gathering power of the human eye (to observe the faint deep sky objects), and with the clear magnification capability (up to about 450-480x usable depending on accessories quality and local seeing conditions) that is particularly desirable for views of the changing major features of the larger planets (Venus, Mars, Jupiter, Saturn in particular).

The Celestar 8 Deluxe features the exact same quality of view as its other Celestron cousins, with a more rigid and adjustable height field tripod and equatorial wedge mount, advanced electronic drive corrector, and a more desireable accessories package for the astronomer. This design is sophisticated yet it does remain simple and fun to use. Set up is quick leaving you time to enjoy yourself and your observing.

The Fastar concept was introduced in 1997 by Celestron (working with Santa Barbara Instruments Group): the "Fastar" telescope concept. Since July of 1998 all C-8 optical tubes provided with the "Celestar 8 Deluxe" and "Ultima 2000" series models have a secondary mirror holder that be interchanged with an optional lens set and CCD camera holder for imaging with either the Celestron Pixcel 255 or Pixcel 237, SBIG ST-5 or ST-237 series CCD cameras - at a very fast f1.95. The post July 1998 C-14 telescopes are similarly equipped to operate at f2.1. This can produce extremely short exposure times of about 25 times faster than was otherwise possible at prime focus. Covering fields of view with a Fastar 8 of as wide as 0.5 x 0.7 degrees - the equivalent of shooting the telescope as a 400mm f1.95 lens! The telescope can also accommodate a variety of optional telecompressor lenses at the axial port to vary the effective focal length and f ratio down to as fast as f3.3.

This "Fastar" concept is now available with orders for C-8 optical tube assemblies as well.

The telescope optical tube assembly weighs only about 10 lbs, and with the attached fork mount and drive base it weighs just 30 lbs. Add the furnished equatorial wedge and tripod and it then weighs 40 lbs. This remains an ideal telescope for the youngster, or elderly astronomer or astrophotographer on the go who can not manage the more substantial or complicated telescopes.

The wedge tilt plate facilitates polar alignment at any latitude between 28 to 90 degrees; by adjusting tripod leveling this can be extended further using caution not to tilt the telescope so far that it becomes unstable. This equatorial wedge accepts an optional "Deluxe Latitude Adjuster" with fine elevation and azimuth adjusting mechanisms and a "no tool knob set" this completely frees one from having to use any wrench at all to set up and polar align the telescope. The telescope fork mount could also be attached to the field tripod directly, thereby using it as an "Altitude-Azimuth" mount; this renders the Celestar 8 Deluxe a choice for those who wish to employ the telescope for applications such as an ultra telephoto or video lens, or as a terrestrial telescope for long distance observing of birds.

The Celestar 8 Deluxe telescope employs a precise "clock drive" tracking system (the early telescope drives were based on modified clocks - these drives rotate a telescope once every 24 hours or so). When properly set up, this mechanism will compensate for the apparent motion of celestial objects across the sky as the Earth rotates. Such a drive system allows you to find and object and precisely center it; there are manual fine motion controls on the fork mount. Find and maintain the object in an eyepiece, where it will remain there permitting you and your friends or family to enjoy the views completly free of any distractions. Furthermore, the setting circles provided on the fork mount allow one to find their way across the sky to find the faint otherwise difficult to find objects using the two dimensional coordinate system employed by professional and amateur astronomers. We highly encourage tracking mounts as this for use by those with young children, or especially if sharing a telescope for astronomy with others. Such a tracking drive system equipped as this is a necessity for astrophotography of most celestial objects.

The electromechanical system incorporates a more rigid fork mount than the Celestar 8 telescope, with a precise worm gear drive system. The electronics control system includes a totally cordless stepper motor drive system with PEC (Periodic Error Correction), an easy recording cycle, four tracking rates including: King, Sidereal, Lunar and Solar, fine correction speed of 0.5X and a slewing speed of 8X sidereal rate. A Declination Control Motor, and Hand Control are furnished. The Hand Control allows fast and slow manual override of the R.A. tracking speed and operation of the optional Declination motor thereby facilitating time exposure astrophotography, and compensating for any errors of Polar Alignment or periodic worm drive errors. The electronic drive corrector is compatible with autoguide CCD systems.

The power-efficient Celestar 8 Deluxe telescope runs off two 9V alkaline batteries so the operation is totally cordless and independent of local power world wide. The Right Ascension drive motor is reversible and so it can operate in either Northern or Southern hemispheres. AC current or 12V operation of the Celestrar 8 Deluxe is possible with the included power adapter cables.

The Celestar 8 Deluxe telescope can be furnished with optional encoders and computer aids to celestial navigation including the Company Seven installed and tested Celestron "Advanced Astro Master" (AAM). This pointing system contains a data base of over 10,000 objects. Once aligned, it will guide you to any one of these objects. Only a simple two star alignment method is needed to get started with your computer assisted telescope - no leveling, longitude or time input needed. The AAM operates from a single 9 volt battery (we sugegst Alkaline or Lithium) for over 30 hours; and it contains an RS-232 serial interface to connect to a personal computer. Other optional systems and interface able planetarium software packages are available. Even though we have some reservations about it and prefer to discuss it in detail with potential buyers, the "Computerised Celestar 8 Deluxe" model with the computer aid to celestial navigation is fun to use, and makes it easy to enjoy our Universe. You can find hundreds or thousands of objects easily. However, we those who wish such performance should seriously consider the better integrated 8" Ultima 2000 computer controlled telescope which also includes features and an accessories package well suited for deep sky astronomy.

Standard accessories of the Celestar 8 Deluxe telescope include: a 9 x 50 Achromatic Finder scope (straight through view), 90 degree Prism Star Diagonal 1-1/4", Visual Back 1-1/4" and a 26mm Plossl Eyepiece 1-1/4" (78x), Declination Motor, Hand Control, AC Adapter (115 v. AC), car battery Adapter (12 v DC), Wedge, Tripod (32" high to the platform, about 39" to the center of the tilt plate).

Specifications of the Celestron 8" Schmidt-Cassegrain Telescope Optical System

The Celestron International company of Torrance, California introduced to the world the first successful mass-production Schmidt Cassegrain telescopes (SCT). In 1970 their 8" aperture model (the original "C-8") telescope was introduced. While the original fork mount has changed over the years and incorporates electronic innovations, and some optical design and manufacture improvements have been incorporated, the Celestron "C-8" remains the most popular and optically acclaimed production 8" SCT in the world.

Left: Cross section illustration of Celestron Schmidt-Cassegrain optical tube assembly

Light entering from the right, passes through the Corrector Lens (1). The light then reflects from the Primary Mirror (2) at the rear of the telescope tube forward to the Secondary Mirror (3). The light then is then reflected back into the Primary Baffle Tube(4), and out of the Rear Cell (5). In this illustration the Rear Cell is shown attached a 90 degree Zenith Prism (6) (or Mirror) diagonal, and an Eyepiece (7).

The Focus Control Knob (8) is rotated clockwise or counter clockwise to move the Primary Mirror forward towards, or to the rear away from the Corrector Lens and Secondary Mirror; this will adjust the position of the focal plane beyond the rear cell of the telescope optical tube assembly where an eyepiece for viewing or a camera for imaging are attached.

The Fastar concept provides for the easy thread off removal of the Secondary Mirror (3) and its holder. In its place is put an optional "Fastar" Field Flattening Lens and CCD camera holder assembly in order to accept any of a number of optional CCD cameras.

Celestron C-8 Optical Tube Assembly Specifications:
Design Schmidt-Cassegrain Catadioptric
Effective Aperture 8 inches, 203.2mm
Nominal Focal Length 80.6 inches, 2048mm
Nominal Focal Ratio f10
Primary Mirror 8.25" Diameter, f1.9, Radius 32", Spherical of fine annealed Pyrex®
Secondary Mirror 2.25" Diameter, Radius 9.7, Spherical (final hand figuring yields a slight asphere) of fine annealed Pyrex®
Mirror Coatings Celestron "Starbright®": 5 step multilayer
Corrector Lens 8" Aperture, 0.190" thick, optical quality crown glass, true aspheric Schmidt curve each side, Mgf2 AR coatings each side
Central Obstruction 2.75"
Highest Useful Magnification Approx. 480x with eyepiece or "negative" lens/Eyepiece combination
Lowest Typical Magnification 37x (1.34 degrees) with 2" 55mm Plossl (5.46mm Exit Pupil), or 32X (1.33 degrees) with 1.25" 40mm Plossl with f6.3 Reducer/Corrector (6.30mm Exit Pupil)
Resolution, Visual Rayleigh Criterion: 0.68 arc seconds, Dawes Limit: 0.57 arc seconds
Resolution, Film 182 lines per mm
Image Scale (CCD or Film) 100 arc seconds per mm, 64 arc seconds per mm
Light Gathering Power 843X Theoretical, Approx. 634X Actual (over human eye with 7mm entrance pupil)
Back Focus 18 + or - 5 inches
Optimum Back Focus Approx. 4 inches; with f6.3 Reducer/Corrector 4" from rear of Reducer
Near Focus Approx. 25' (Camera or Visual)
Optical Tube Dimension Length 16", Diameter 9", Front Cell Diameter 9-1/8"
Optimum Back Focus Approx. 4 inches; with f6.3 Reducer/Corrector 4" from rear of Reducer

*The telescope can accommodate a variety of Telecompressor lenses to vary the effective focal length and f ratio. And beginning in May 1998 all worm driven Celestron 8 telescopes will be equipped with an interchangeable secondary mirror holder to permit the installation of an optional "Fastar 8" CCD camera holder. This permits users of several of our popular CCD cameras to run the cameras at the secondary mirror holder position at f1.95 with the 8", or f2.1 with the C-14. This results in incredibly wide fields of view, and very short exposure times. This is an option available only for the new 8" and 14" Celestron optical tube assemblies; the "Fastar" logo is affixed to those optical tubes that can accommodate the option.

Download the publication Celestron C-8 Telescope, the complete instruction manual which we include with the Celestar 8 and the Celestar 8 Deluxe telescopes. A very good overview about the use of 8 inch Schmidt-Cassegrain fork equatorial telescopes, set up and operation, by Celestron International (in Acrobat Reader ".pdf" format).

Celestron Schmidt-Cassegrain Telescopes
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