Celestron Advanced VX 8" SCT

8" Schmidt-Cassegrain Optics: 2032mm at f/10

Celestron traces the C8 tube to the revolutionary C8 that transformed the hobby, and says the 8" tube offers 84% more light gathering ability than a 6" telescope; the Schmidt-Cassegrain design eliminates chromatic aberration, making it a good choice for astroimaging. The aluminum tube is 432mm (17") long and 238mm (9.37") in diameter, weighs 12.5 lbs (5.67 kg) and mounts with a CG-5 dovetail bar.

The 203.2mm aperture and 2032mm focal length give 843x the light gathering power of the eye, a limiting stellar magnitude of 14 and a resolution of 0.69 arc seconds (Rayleigh) or 0.57 arc seconds (Dawes). The secondary obstruction is 31% by diameter and 9.77% by area.

The included 25mm eyepiece gives 81x; the highest useful magnification is 480x and the lowest is 29x. A 6x30 finderscope and a 1.25" star diagonal are included.

StarBright XLT Coatings, Focusing and Collimation

StarBright XLT is Celestron's coating system, built from three parts: enhanced multi-layer mirror coatings of aluminum, SiO2 and TiO2, with reflectivity fairly flat across the spectrum for both imaging and visual use; multi-layer anti-reflective coatings of magnesium fluoride and hafnium dioxide; and water white glass instead of soda lime glass for the corrector. Water white glass transmits about 90.5% of light uncoated, 3.5% more than soda lime glass, and reaches an average transmission of 97.4% with the StarBright XLT anti-reflective coatings. StarBright XLT lets you discern subtle details while viewing the Moon and planets as well as faint galaxies and nebulae.

Focusing moves the primary mirror, which slides on the primary baffle tube; the focus knob sits on the rear cell just below the star diagonal, and it takes about 30 turns to go from close focus to infinity. Make the final focus turn counterclockwise so the mirror moves against gravity, which minimizes any mirror shift, and start on a bright object such as the Moon or a planet, since out-of-focus stars are very diffuse.

Celestron collimates every telescope at the factory and checks it before shipping. If it is jarred in transport, you can adjust the tilt of the secondary mirror with the three collimation screws on the secondary housing, the only adjustment available to the user. To check, defocus a star at least 20 degrees above the horizon with a high-power eyepiece: the dark shadow of the secondary should sit centered in the bright rings on both sides of focus. If you are unsure whether it needs adjustment, it is likely fine and best left alone. Before checking collimation, let the telescope reach thermal equilibrium with its surroundings, allowing 45 minutes if you move it between large temperature extremes, such as from a heated house into the cold night air.

The Advanced VX Mount: 30 lb Payload and DC Servo Motors

The Advanced VX sets a standard in mid-level telescopes, with many of the features found on Celestron's most sophisticated German equatorial mounts: All-Star Polar Alignment, Celestron PWI telescope control software and permanently programmable periodic error correction (PPEC). It is the smallest of Celestron's German equatorial mounts. The Advanced VX carries 30 lbs, not including the counterweight. Features include high-torque, low-cog DC servo motors with encoders on both axes to smoothly drive heavier loads, permanently programmable periodic error correction (PPEC), a dedicated autoguider port, large, easy-to-access polar alignment knobs and an ergonomic design that disassembles into compact, portable pieces. The latitude range is 7° to 77°, and the mount slews at nine speeds up to 4° per second, tracking at sidereal, lunar and solar rates in EQ North and EQ South.

The 30 lb payload, which does not include the counterweights, gives a sturdy platform for any of the Advanced VX optical tubes, even with optional accessories such as StarSense AutoAlign, a focus motor, a finderscope and a camera.

To balance in R.A., loosen the R.A. clutch lever with the counterweight bar horizontal and move the counterweight until the telescope stays put; in Dec, loosen the DEC clutch with the tube level and slide the tube in the saddle. Celestron's tip for imaging is a very slight imbalance, toward the counterweight side when the tube is west of the mount and toward the tube when it is east, so the worm gear always pushes against a slight load.

Dual Saddle Plate and the 2" Steel Tripod

The dual saddle plate takes the narrower 1.75" V-plate (CG-5, Vixen-style) dovetail or the wider 3" (75mm) D-plate style used on Celestron's CGEM, CGX and CGX-L. It ships set up for the V-plate; removing two bolts on the left side of the saddle with a 6mm Allen key converts it for the wider bar. On its product page Celestron adds that the saddle takes Vixen format dovetails 100mm or longer, and that other makers' D format plates are not compatible, whoever makes them; the wide side is for Celestron's CGE-style bar.

The tripod is impressive for its class: 2" (50.8mm) stainless steel legs give an extra-wide stance for improved stability, and with the mount it adjusts from 1118mm to 1626mm (44" to 64"). The head weighs 17 lbs (7.71 kg), the tripod 18 lbs (8.16 kg). This kit includes one 12 lb counterweight.

The tripod comes fully assembled, with an all-metal center leg brace and accessory tray for rock solid support. The alignment peg ships between two legs, so the counterweight bar extends between them; you can move it over a leg, but observers at lower latitudes will prefer it between two legs so the counterweight clears the tripod at the bottom of its swing. The azimuth adjustment knobs are removed for shipping and attach to the mount at setup.

NexStar+ Hand Control and Celestron PWI Software

The NexStar+ hand control has an LCD and 19 fiber-optic backlit LED buttons, and its database holds over 40,000 objects, 100 user defined programmable objects and enhanced information on over 200 objects. With automatic slewing and menu descriptions, any level of astronomer can master the mount in just a few observing sessions; beginners can start with the Sky Tour, which finds the most interesting objects in the sky and slews to each one.

Alignment procedures are 2-Star, 1-Star, Solar System, Last Alignment and Quick Align, and calibration stars added after a two-star alignment improve pointing accuracy. The mount tracks at sidereal, solar and lunar rates in EQ North and EQ South modes.

Celestron includes Celestron PWI (CPWI) telescope control software, with a graphical planetarium interface and PointXP mount modelling that adds 100+ points to the alignment model, saving and reloading the alignment and parking the scope for remote observatory setups, and a complete ASCOM telescope interface for third-party software. A free download of Starry Night Special Edition, which can also control the telescope, and the SkyPortal app are included too.

Imaging: PPEC, All-Star Polar Alignment and Slew Limits

Periodic Error Correction improves tracking by reducing the amplitude of the worm errors. Recording PEC takes three steps: the mount indexes its worm gear, you guide with an autoguider for at least 10 minutes (one full worm revolution) while it records your corrections, and then you play them back. The mount retains the recording, and PEC is meant for advanced astrophotography and still needs careful guiding.

All-Star Polar Alignment lets you polar align accurately using any bright star, even when the celestial pole is hidden. After a two-star alignment with at least one calibration star, you slew to a bright star from the Named Star list, ideally high in the sky and near the meridian, and choose Polar Align, then Align Mount. The mount syncs on the star and slews to where it should be if accurately polar aligned, and you center it with the mount's latitude and azimuth adjustments, not the hand control's direction buttons.

The R.A. slew limits can be set anywhere from 40° above level to 20° below, so the mount can keep tracking past the meridian without flipping, or stop before an imaging cable runs out of length, and the Meridian setting (Favor Current, Favor West, Favor East or Disable) chooses which side of the mount the tube stays on. Built-in calibration routines compensate for the mechanical variation found in every German equatorial mount; running them is recommended, and most need doing only once.

The 8" tube is Fastar/HyperStar compatible: the secondary mirror can be removed and replaced with a lens assembly, sold separately and not included, so that a camera works at the f/2 focus of the primary mirror at the front of the telescope. Celestron's SCT manual says f/2 needs exposures about 25 times shorter than f/10, with a field of view 5 times larger and the object 1/5 the size. The secondary mirror should never be removed except to install the Fastar lens assembly.

Ports, PC Control and Power

The mount has a hand control port, two AUX ports for optional accessories such as StarSense AutoAlign and an autoguider port. A mini USB cable (not included) from a computer to the port on the bottom of the NexStar+ hand control links it to software and updates the hand control firmware without external power or the mount.

Power is 12V DC at 3.5A, tip positive. The supplied car battery adapter cable plugs into a car's cigarette lighter outlet or a portable power supply, or you can use Celestron's optional 12V AC adapter; use only adapters Celestron supplies, as others may damage the electronics and void the warranty.