LT6-ACF 6" Advanced Coma-Free go-to altazimuth

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ACF optics
Features of this Telescope’s Optical System . . .
  • Advanced Coma-Free catadioptric designed to emulate the optical performance of a Ritchey-Chrétien telescope: The traditional two-mirror Ritchey-Chrétien (R-C) design uses two large hyperbolic primary and secondary mirrors to produce images that are free from coma over a wide field. Because of this wide coma-free field and a relatively fast focal ratio, the Ritchey-Chrétien design is particularly well suited to astrophotography. The R-C is the design of choice for most of the major professional observatory telescopes built in the last half-century. For example, the Hubble Space Telescope and the twin 10-meter Keck telescopes in Hawaii are Ritchey-Chrétiens.
        However, because of the complexity of fabricating and testing a large aperture hyperbolic mirror (just ask the people who built the initially-flawed, but not discovered until it was in space, Hubble Space Telescope), traditional large aperture two-mirror Ritchey-Chrétiens are very expensive to manufacture and purchase, too expensive for many amateur astronomers.
        To emulate the coma-free performance of a true R-C telescope, while keeping the cost very much within reason, each Meade Advanced Coma-Free (ACF) catadioptric optical system uses a full aperture aspheric corrector lens in conjunction with a simple spherical primary mirror. This creates a two-element primary mirror system that performs like an R-C’s single hyperbolic primary mirror from the optical point of view of the system’s secondary mirror. The hyperbolic secondary mirror itself is mounted directly on the rear of the corrector lens, rather than in the traditional R-C’s conventional spider vane assembly. This eliminates the image-degrading diffraction spikes of the secondary mirror support structure visible in commercial R-C scope images. The result is R-C-class coma-free wide-field performance, at only a fraction the cost of most true R-C systems.
        The corrector-modified design would itself be expensive to fabricate were it not for Meade’s more than a quarter-century of experience making Schmidt-Cassegrain correctors, which are in the same optical family as the corrector needed for the coma-free design of the ACF scopes. An additional benefit of the full aperture corrector in the ACF design is slightly better correction for astigmatism than the traditional R-C design.
        In addition, the ACF design, due to its front corrector plate, is a closed tube design. This keeps the primary optical components protected from dust, moisture and other contaminants that might fall on the optical surfaces of the primary and secondary mirrors as can happen with the traditional open-tube R-C design.
        While the ACF scopes may not be traditional R-C designs, their performance is R-C-like in all important characteristics. A review in Sky & Telescope magazine of the ground-breaking predecessor of the Meade ACF optics said the bottom line is that the optics do “indeed perform like a Ritchey-Chrétien.” Another such review, in Astronomy magazine said, “This scope delivers Ritchey-Chrétien-like performance at a fraction of the cost.”

    • Low thermal expansion mirrors: The primary and secondary mirrors are made of low thermal expansion Pyrex to limit any possible focal length change as the temperature drops. This reduces the possibility of the focus changing during critical through-the-scope CCD imaging.

    • Oversized primary mirrors: The diameter of the primary mirror of each ACF scope is larger than the diameter of the corrector lens at the front of its optical tube that admits the light. For example, the primary mirror of the 8” scope is actually 8.25” in diameter, compared to the 8” diameter of the corrector lens. Oversizing the primary mirror in this way gives you a wider fully-illuminated field than a conventional catadioptric scope whose corrector and primary mirror are the same size. The result is a gain of 5% to 8% more off-axis light available to your eye or camera, depending on the telescope model.

    • Fully multicoated UHTC (Ultra High Transmission Coatings) optics: The primary and secondary mirrors are vacuum-coated with aluminum, enhanced with multiple layers of titanium dioxide and silicon dioxide for increased reflectivity. A final layer of durable silicon monoxide (quartz) assures long life.
          A series of anti-reflective coatings of aluminum oxide, titanium dioxide, and magnesium fluoride are vacuum-deposited on both sides of the full aperture corrector plate. These antireflection multicoatings provide a high 99.8% light transmission per surface, versus a per-surface transmission of 98.7% for standard single-layer coatings. Overall light throughput (the amount of light collected by the objective lens that actually reaches your eye or camera) is approximately 89% at the focal plane.
          UHTC multicoatings provide a 15% increase in light throughput compared with standard single-layer coatings. . For example, they effectively add the equivalent of a little more than four-tenths of an inch of extra light-gathering aperture to the performance of the 6” optical system – but with no increase in actual size or weight. The UHTC multicoatings also improve contrast, for lunar and planetary images that appear sharper and more crisply defined.

    • Fully baffled optics: A cylindrical baffle around the secondary mirror, in combination with the cylindrical baffle tube projecting from the center of the primary mirror, prevents stray off-axis light from reaching the image plane. In addition, a series of field stops machined into the inner surface of the central baffle tube effectively eliminates undesirable light which might reflect from the inside surface of the tube. The result of these baffle systems is improved contrast in lunar, planetary, and deep space observing alike.
This Meade LT-6ACF telescope has:

• the latest 6” f/10 Advanced Coma-Free catadioptric optical system with images that rival professional Ritchey-Chrétien telescope performance
• UHTC multicoated optics
• computerized go-to altazimuth mount and tripod
• AudioStar™ talking computer hand control with 30,000+ object memory
• red dot finderscope
• 26mm Series 5000 Plössl eyepiece (59x) for a wide 1.02° field of view

    The Meade LT-6ACF go-to 6” f/10 provides the backyard astronomer with the latest Advanced Coma-Free optics at the lowest price ever for a state-of-the-art optical system. The Meade LT-6ACF is a scope that can keep you happily observing for the rest of your life, at a price that you can afford right now.

    This Meade 6” LT-6ACF catadioptric brings the image quality of a professional observatory to your back yard. Its Advanced Coma-Free optics have a flat, coma-free field that is visibly similar to that of the Ritchey-Chrétien design optics used in most professional observatory telescopes and the Hubble Space Telescope, but at a mere fraction the cost of a true Ritchey-Chrétien.

    The scope’s standard equipment AudioStar™ computer is amazingly simple to set up and operate. You don't have to know Polaris from the Pleiades, or Albireo from Zubeneschamali. All you have to do is level the scope, point it North, and tell the AudioStar™ where you are on Earth and the time and date. The AudioStar™ computer will do the rest, aligning the scope on the skies and letting you locate dozens of deep space objects like a seasoned observer your first night out.

    Once aligned, the speaker built into the AudioStar™ computer hand control of the LT-6ACF and its unique Astronomer Inside™ software can provide you with more than four hours of fascinating audio descriptions of the objects you are observing. Astronomer Inside™ puts the experience and astronomical knowledge of a professional astronomer in the palm of your hand.

This Meade LT-6ACF Telescope’s Optical System . . .

  • Advanced Coma-Free catadioptric designed to emulate the optical performance of a Ritchey-Chrétien telescope: 6” aperture (1524mm focal length f/10). Pyrex primary mirror. Fully-multicoated UHTC (Ultra High Transmission Coatings) optics for the highest possible image brightness. Corrector made from premium clear water white Schott glass. Aluminum tube construction, 7” diameter x 14.2” length, with glare-stop baffling. Guaranteed diffraction-limited performance. The scope has a standard Schmidt-Cassegrain rear cell thread, allowing the use of most SCT accessories manufactured over the past 30 years. For more details, click on the “optics” icon above.

  • Finderscope: A straight-through red dot finder allows easy non-magnified views of the sky, with a projected red dot of light showing exactly where the scope is pointed at all times.

  • Star diagonal: 1.25” 90° prism type.

  • Eyepiece: 1.25” 26mm Series 5000 Plössl (59x). The eyepiece field of view is 1.02°, a trifle wider than the full Moon, for expansive lunar and deep space views.

This Telescope’s Mount . . .

  • Fork mount/drive system: Light-weight, but rigid, die-cast aluminum single fork arm damps vibrations quickly. There is a carrying handle at the top of the fork arm. The mount includes 12volt DC slewing and tracking motors with 4.875” worm gear drives in both altitude and azimuth.
    The scope is powered by eight user-supplied C-cell batteries that store in the drive base so you can use the LT-6ACF in the field or your backyard without the need for a separate battery pack or AC power supply. Battery life is typically about 20 hours, depending on the amount of slewing you do and the temperature (very cold temperatures reduce battery life). An optional #RCXAC adapter is available to allow you to power the scope from 110-120volt 60Hz AC household current in your backyard to conserve battery life. A #607 cigarette lighter plug adapter is also available to power the scope from your car's cigarette lighter plug or a rechargeable battery for extended use in the field.
    The scope is surprisingly light. Its optical tube, fork arm, and drive base weigh only 30 pounds, while the adjustable height tripod weighs only 9 pounds more. This light weight/two-part system makes it easy for one person to transport and assemble the scope, even a youngster.

  • Adjustable height tripod: The rugged steel tripod adjusts in height from 25.5” to 43.5”. Its steel legs damp vibrations quickly, and a center leg brace adds rigidity. Three 1.25” diameter holes in the leg brace can hold eyepieces while observing. A single threaded rod with a large hand-tighten knob simultaneously holds the scope firmly on the tripod and locks the legs rigidly in the most stable position.

  • AudioStar™ computer: The LT-6ACF’s AudioStar™ computer hand control plugs into the telescope’s fork arm to permit a wide array of telescope options. First and foremost is its automatic go-to capability. The AudioStar™ computer can show you the planets and thousands of deep space objects (and tell you about them with over four hours of professionally recorded audio) the very first night you use your scope – even if you've never used a telescope before!
    At the push of a button, the LT-6ACF will move at a fast 6.5° per second to any of the 30,223 objects in its database and center it with five arc minute accuracy, trainable to three arc minute accuracy (the field of view of the supplied eyepiece is about 53 arc minutes wide). You can choose from 13,235 deep-sky objects from the complete Messier, Caldwell, IC, and NGC catalogs (sorted by name and type). Also included are 16,888 stars sorted by name, SAO catalog number, and by whether they are double or variable stars.
    The AudioStar™ will also locate the centroids of all 88 constellations and 50 objects in the solar system (8 major planets from Mercury to Pluto; the Moon; 26 asteroids; and 15 periodic comets). You can use it to track 50 Earth satellites, including the International Space Station and the Hubble space telescope, plus any of 200 user-defined objects. You can also automatically move to any object that’s not in the database simply by entering its right ascension and declination coordinates.
    The AudioStar™ moves the LT-6ACF at any of nine user-selectable slewing and guiding speeds: 6.5°/sec, 3°/sec, and 1.5°/sec for slewing and centering; as well as 128x, 64x, 16x, 8x, and 2x the sidereal rate for centering and astrophotographic guiding. In addition, there are standard solar, lunar, and sidereal tracking rates with 2000 precision-selected incremental rates that permit observatory-level precision in tracking the Moon and planets.
    The AudioStar™ computer includes hundreds of special event menus, guided tours of the night’s best objects, a glossary, utility functions, and telescope status options. It also allows fast alignment of the telescope in the altazimuth mode using any of three alignment methods, including Meade’s proprietary Easy Align method.

  • AudioStar™ computer operation: The operation of the LT-6ACF is simplicity itself. Once you mount the scope on its tripod, aim the scope north and level the optical tube. Enter your observing location’s latitude and longitude into the AudioStar™ computer hand control. This needs only to be done once, as the scope will keep the location in its memory, as well as that of several other favorite observing sites that you can call up at will. Enter the time. The LT-6ACF will orient itself to the sky and slew at 6.5 degrees per second to the first of two alignment stars. If that star is not precisely centered, a touch or two on the AudioStar™ hand control directional push buttons quickly centers it. Do the same with the second alignment star the scope moves to and you’re ready to observe. That's it!
    It takes only a few minutes to begin observing. For the rest of the evening, a computer in the AudioStar™ controls the scope’s altitude and azimuth motors to keep you precisely centered on whatever you aim at, for as long as you want to observe.

  • AutoStar Software Suite: This new software package is included as standard equipment with the LT-6ACF. It is designed to integrate the telescope with your PC or laptop computer for an enhanced range of performance features. The AutoStar Software Suite includes a planetarium program with a database of 19,000,000 stars and deep space objects for display on your computer screen. It includes all the standard planetarium program features for stand-alone use when nights are cloudy.
    In addition, if you connect the scope to your computer (using the supplied cable), the program lets you click on objects in the sky map displayed on the computer screen and have your telescope automatically slew to those objects. You can automatically generate AutoStar Tours of favorite objects with a simple point and click.
    The software lets you control all AutoStar functions from your computer or laptop. You can use it to create observing lists and download them to the AutoStar for use in the field when you don’t have your computer or laptop with you. You can use it to control your telescope remotely via the Internet. “Talking Telescope” software (included) converts AutoStar text displays to synthesized speech through your computer speaker. An AutoStar Update Tool keeps your AutoStar current by downloading the latest system firmware updates and comet, asteroid, and satellite data over the internet from Meade’s website.

    If you’re one of those busy people whose schedule doesn’t leave you much time to enjoy astronomy, the easy to use fully-computerized Meade LT-6ACF with its unique Astronomer Inside™ software and talking AudioStar™ computer hand control will make the most of your limited observing opportunities. The simple two-piece altazimuth design of the LT-6ACF makes setup fast and easy. The rapid alignment features of the AudioStar™ computer and its simplified menus start you observing in only a matter of minutes. The wide array of objects in the LT-6ACF database, and the 5 arc minute pointing accuracy of the AudioStar™ computer, accurately speed you from object to object with no frustrating hunting or star hopping. With the LT-6ACF, you’ll spend more of your time looking at objects and less time looking for them.

    This 6” scope It is big enough to keep you happily observing for many years to come, portable enough to make it easy for spur of the moment observing, with premium coma-free optical performance that will make your observing a visual delight . . . all at a price that won’t break the bank.

Supplied Eyepiece:
The eyepiece that is supplied with this telescope.
Highest Useful Magnification:
This is the highest visual power a telescope can achieve before the image becomes too dim for useful observing (generally at about 50x to 60x per inch of telescope aperture). However, this power is very often unreachable due to turbulence in our atmosphere that makes the image too blurry and unstable to see any detail.

On nights of less-than-perfect seeing, medium to low power planetary, binary star, and globular cluster observing (at 25x to 30x per inch of aperture or less) is usually more enjoyable than fruitlessly attempting to push a telescope's magnification to its theoretical limits. Very high powers are generally best reserved for planetary observations and binary star splitting.

Small aperture telescopes can usually use more power per inch of aperture on any given night than larger telescopes, as they look through a smaller column of air and see less of the turbulence in our atmosphere. While some observers use up to 100x per inch of refractor aperture on Mars and Jupiter, the actual number of minutes they spend observing at such powers is small in relation to the number of hours they spend waiting for the atmosphere to stabilize enough for them to use such very high powers.
Visual Limiting Magnitude:
This is the magnitude (or brightness) of the faintest star that can be seen with a telescope. The larger the number, the fainter the star that can be seen. An approximate formula for determining the visual limiting magnitude of a telescope is 7.5 + 5 log aperture (in cm).

This is the formula that we use with all of the telescopes we carry, so that our published specs will be consistent from aperture to aperture, from manufacturer to manufacturer. Some telescope makers may use other unspecified methods to determine the limiting magnitude, so their published figures may differ from ours.

Keep in mind that this formula does not take into account light loss within the scope, seeing conditions, the observer’s age (visual performance decreases as we get older), the telescope’s age (the reflectivity of telescope mirrors decreases as they get older), etc. The limiting magnitudes specified by manufacturers for their telescopes assume very dark skies, trained observers, and excellent atmospheric transparency – and are therefore rarely obtainable under average observing conditions. The photographic limiting magnitude is always greater than the visual (typically by two magnitudes).

Focal Length:
This is the length of the effective optical path of a telescopeor eyepiece (the distance from the main mirror or lens where the lightis gathered to the point where the prime focus image is formed). Focallength is typically expressed in millimeters.

The longer the focallength, the higher the magnification and the narrower the field of viewwith any given eyepiece. The shorter the focal length, the lower themagnification and the wider the field of view with the same eyepiece.

Focal Ratio:
This is the ‘speed’ of a telescope’s optics, found by dividing the focal length by the aperture. The smaller the f/number, the lower the magnification, the wider the field, and the brighter the image with any given eyepiece or camera.

Fast f/4 to f/5 focal ratios are generally best for lower power wide field observing and deep space photography. Slow f/11 to f/15 focal ratios are usually better suited to higher power lunar, planetary, and binary star observing and high power photography. Medium f/6 to f/10 focal ratios work well with either.

An f/5 system can photograph a nebula or other faint extended deep space object in one-fourth the time of an f/10 system, but the image will be only one-half as large. Point sources, such as stars, are recorded based on the aperture, however, rather than the focal ratio – so that the larger the aperture, the fainter the star you can see or photograph, no matter what the focal ratio.

This is the ability of a telescope to separate closely-spaced binary stars into two distinct objects, measured in seconds of arc. One arc second equals 1/3600th of a degree and is about the width of a 25-cent coin at a distance of three miles! In essence, resolution is a measure of how much detail a telescope can reveal. The resolution values on our website are derived using the Dawes’ limit formula.

Dawes’ limit only applies to point sources of light (stars). Smaller separations can be resolved in extended objects, such as the planets. For example, Cassini’s Division in the rings of Saturn (0.5 arc seconds across), was discovered using a 2.5” telescope – which has a Dawes’ limit of 1.8 arc seconds!

The ability of a telescope to resolve to Dawes’ limit is usually much more affected by seeing conditions, by the difference in brightness between the binary star components, and by the observer’s visual acuity, than it is by the optical quality of the telescope.

0.76 arc seconds
This is the diameter of the light-gathering main mirror or objective lens of a telescope. In general, the larger the aperture, the better the resolution and the fainter the objects you can see.
The weight of this product.
37 lbs.
Heaviest Single Component:
The weight of the heaviest component in this package.
28 lbs.
Telescope Type:
The optical design of a telescope.  Telescope type is classified by three primary optical designs (refractor, reflector, or catadioptric), by sub-designs of these types, or by the task they perform.
Advanced Coma-Free
Based on Astronomy magazine’s telescope "report cards", scopes of this size and type generally perform as follows . . .
Terrestrial Observation:
Observing terrestrial objects (nature studies, birding, etc.) is usually possible only with refractor and catadioptric telescopes, and convenient only when the scope is on an altazimuth mount or photo tripod. Most reflectors cannot be used for terrestrial observing. Scopes with apertures under 5" to 6" are generally most useful for terrestrial observing due to atmospheric conditions (heat waves and mirage, dust, haze, etc.) that degrade the image quality in larger scopes. 
Lunar Observation:
Visual observation of the Moon is possible with any telescope. Larger aperture scopes will provide more detail than smaller scopes, thereby getting a higher score in this category, but may require an eyepiece filter to cut down the greater glare from the Moon's sunlit surface so small details can be seen more easily. Lunar observing is more rewarding when the Moon is waxing or waning as the changing sun angle casts constantly varying shadows to reveal craters and surface features by the hundreds.  
Planetary Observation:
Binary and Star Cluster Observation:
Very Good
Galaxy and Nebula Observation:
Terrestrial Photography:
Photographing terrestrial objects (wildlife, scenery, etc.) is usually possible only with refractor and catadioptric telescopes, and convenient only when the scope is on an altazimuth mount or photo tripod. Most reflectors cannot be used for terrestrial photography. Scopes with focal ratios of f/10 and faster and apertures under 5" to 6" are generally the most useful for terrestrial photography due to atmospheric conditions (heat waves and mirage, dust, haze, etc.) that degrade the image quality in larger scopes.
Lunar Photography:
Photography of the Moon is possible with virtually any telescope, using a 35mm camera, DSLR, or CCD-based webcam (planetary imager). While an equatorial mount with a motor drive is not strictly essential, as the exposure times will be very short, such a mount would be helpful to improve image sharpness, particularly with webcam-type cameras that take a series of exposures over time and stack them together. Reflectors may require a Barlow lens to let the camera reach focus. 
Planetary Photography:
Star Cluster / Nebula / Galaxy Photography:
1 year
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General Accessories
Drive Motors and Drive Accessories (3)
Power Tank 7 Amp-hour 12V DC rechargeable battery
by Celestron
Meade #607 Car Battery Cord
by Meade
Meade AC power adapter for Meade telescopes
by Meade
Extended Service Program (4)
Three-Year Advance Shipping Program
by Meade
Five-Year Advance Shipping Program
by Meade
Three-Year Sky Assurance™ For Meade telescopes priced between $750 and $1199.99
by Meade
Five-Year Sky Assurance™ For Meade telescopes priced between $750 and $1199.99
by Meade
Visual Accessories
Accessory Kits (1)
Series 4000 Super Plössl 1.25" 6-eyepiece and filter set
by Meade
  • 6” f/10 ACF (Advanced Coma-Free) catadioptric optical tube assembly with UHTC optics (multicoated mirrors and a multicoated corrector lens)
  • Single-arm fork mount with dual-axis 4.875” worm gears and control panel
  • Electric slow-motion controls on both axes
  • AudioStar hand controller with Astronomer Inside software and digital readout display, 9-speed drive controls on both axes, and go-to controller
  • 30,223-object onboard celestial software library
  • Internal battery port accepts 8 (user-supplied) C-cells (optional adapters permit powering from either 12vDC auto cigarette lighter plug or from 110-120VAC home outlet)
  • Red dot non-magnifying finder
  • 1.25” prism star diagonal
  • Series 5000 Plössl 26mm eyepiece (59x)
  • AutoStar Astronomer’s Edition Software Suite
  • Adjustable height field tripod
  • Operating instructions.
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Meade - LT6-ACF 6" Advanced Coma-Free Go-to altazimuth

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Meade - LT6-ACF 6" Advanced Coma-Free Go-to altazimuthFull length image of the LT6ACF on its tripod.Feature image name not indicated
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Our Product #: LT6ACF
Manufacturer Product #: 0610-04-10
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LIMITED QUANTITY. This Meade 6” LT-6ACF puts the newest Advanced Coma-Free (ACF) optics with UHTC optical multicoatings on an easily-transported battery-powered go-to altazimuth mount with adjustable tripod. It has a unique AudioStar computer hand control that can talk to you about the thousands of celestial objects it can find and track for you. And it combines them all at the lowest price ever for a scope with state-of-the-art coma-free optics . . .

. . . our 38th year