AstroMaster 70 AZ, 2.8" Altazimuth refractor

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The Celestron 70mm AstroMaster altazimuth refractor is a good choice for a beginning astronomer who also has an eye for nature. This sensibly-priced refractor optical system is a good way to begin your journey into the night sky, as well as exploring nature during the day. It provides you with detailed high-contrast views of the Moon and planets in the heavens, as well as sharp views of birds and animals across a lake or across the way.

The construction of the optical system is first rate, as the AstroMaster has all-glass optical components, with high transmission optical coatings for enhanced image brightness and clarity. The mount has a convenient pan handle, like the control handle on a camera tripod, for guiding the scope around the skies or the landscape. A built-in clutch makes operating the well-balanced scope with the pan handle smooth and easy. The scope assembles in only a minute or two, with no tools required.

Once you have scanned your way through the solar system and the Milky Way, you can use the AstroMaster to look at things closer to home. The altazimuth mount will let you easily track objects on the ground and allow you to get a closer look at nature and your surroundings.

The AstroMaster 70 has a light grasp 100 times that of the sharpest eye for nighttime and twilight use. It can also resolve details ten times smaller than you can see clearly with your unaided eye. Combine that light grasp and sharpness with its two eyepieces (a 20mm for 45x magnification and a 10mm for 90x), and you have the ability to see many, many celestial and terrestrial objects that are simply invisible to the unaided eye. Some chromatic aberration (a faint halo of violet light around the Moon and planets when observing at night) is visible in the AstroMaster 70, as it is in all achromatic refractor telescopes.

This Telescope’s Optical System . . .

  • Refractor optical tube: 70mm (2.8”) aperture. 900mm focal length f/12.9 achromatic doublet lens with all-glass optics. No plastic lenses.

  • Coated optics: The two-element objective lens has a layer of magnesium fluoride antireflection coatings on all air-to-glass surfaces for high light transmission and good contrast.

  • Dovetail mount: A quick-release dovetail bar on the optical tube fits into a dovetail slot on the mount. The optical tube can be installed and locked firmly in place in seconds using a single no-tool knob on the mount.

  • Dew shield: A dew shield (an extension of the optical tube that’s threaded onto the front of the objective lens) slows the formation of dew on the lens in cold weather. This extends your undisturbed observing time. It also improves the contrast when observing objects on the ground during the day.

  • Rack and pinion focuser: The well-made 1.25” focuser has dual focusing knobs for precise image control with either hand. The good-sized focus knobs are easy to operate, even while wearing gloves or mittens in cold weather.

  • Star diagonal: The 90° viewing angle 1.25” star diagonal (eyepiece holder) allows comfortable viewing when looking overhead at the sky. It provides erect mirror image views (objects are reversed left for right). This is not a problem when observing the stars and planets, but may be disconcerting during terrestrial observing, as printing (license plates, the names on boats, etc.) will be backwards. For most nature studies this isn’t a problem, though, because a duck still looks like a duck whether he’s facing left or right. An optional #6329 45° viewing angle image-erecting diagonal is available if right-reading images are essential. It gives you correctly oriented images and more comfortable extended terrestrial observing.

  • Two eyepieces: You get a high power 1.25” 10mm (90x) eyepiece and a low power 1.25” 20mm (45x) with a 1.1° field of view (over twice the diameter of the full Moon). Both eyepieces have antireflection coatings on their lens surfaces for sharp images and good contrast.

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

This Telescope’s Mount . . .

  • Altazimuth mount: The altazimuth mount with camera tripod-style pan handle provides right/left and up/down motions. This is suitable for casual astronomical observing, and will let you easily track objects on the ground to allow you to get a closer look at nature and your surroundings. An adjustable tension clutch knob at the base of the mount allows you to lock the tube in place or to adjust the drag on the scope during right/left motions. This lets you control how smoothly the mount moves as you move the tube left or right to follow objects moving across the sky or on the land. A simple twist on the pan handle locks the scope in place up and down, as well as letting you adjust the drag on the scope to set the travel smoothness when adjusting its position vertically. The optical tube is well balanced, but keeping your hand on the pan handle at all times when the clutches are unlocked would be a sensible safety precaution.

  • Tripod: The lightweight pre-assembled tripod has 1.5” diameter stainless steel legs to provide a rigid and stable observing platform. It easily adjusts in height with no tools needed for standing or seated observations through the telescope. Spreader bars lock the legs firmly open when the tripod is set up. The tripod includes a convenient accessory tray that attaches to the spreader bars to hold your eyepieces and accessories close at hand and up out of the dew-soaked grass. The no-tool lock knobs that adjust the leg height of the tripod are on the inside of the legs so they won’t snag on clothing in the dark, a thoughtful touch that’s sure to be appreciated.

  • Software: Comes with TheSky Level 1 sky-charting CD-ROM that has a database of 10,000 stars and objects it can plot and display on your Windows-based computer screen. That’s enough solar system and deep space detail to keep you busy observing for years, yet not so much that you’re overwhelmed by charts showing much more detail than your scope can usefully reveal. Custom sky chart printing lets you print out eyepiece finder charts to use with your telescope to help you locate and identify the planets and many famous and faint deep space nebulas, galaxies, and star clusters by star-hopping from object to object using your scope’s pan handle control. There are 75 full color images of well-known celestial objects to help you identify them through your scope.

  • Two year warranty: As an expression of Celestron’s confidence in the quality of their products, the AstroMaster is protected by Celestron’s two-year limited warranty against flaws in materials and workmanship.
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.
150x
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).

11.7
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.

900mm
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.

f/12.9
Resolution:
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.

1.65 arc seconds
Aperture:
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.
2.8"
Weight:
The weight of this product.
18 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.
Refractor
 
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. 
Yes
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.  
Good
Planetary Observation:
Fair
Binary and Star Cluster Observation:
Fair
Galaxy and Nebula Observation:
Fair
Photography:
Yes
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.
Yes
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. 
Yes
Planetary Photography:
No
Star Cluster / Nebula / Galaxy Photography:
No
Warranty:
2 years
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1. Russell on 9/9/2012, said: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics
Attention: For beginners that aren't sure about jumping in with 'both feet' - THIS is your telescope. I surely wish I could have had this refractor when I started out in astronomy. This scope is a keeper! No matter how many telescopes you eventually buy, this one will always have a spot on your list. It is light in weight with a solid tripod and alt/az mount, perfect for viewing the Moon and planets but very good for distant vistas on our planet too. Wait until you see the craters and mountains of our Moon jump into sharp clear view. And Saturn will appear nearly unreal - textbook sharp - as a picture.
This is a quality, 'almost' 3-Inch refractor. It has the 'heart' of a 75mm scope. At a much lower price and no detectable difference between the Astromaster & the 3" refractor. A great deal for the young beginner - AND.. for the old pro's like me. A fun telescope !
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General Accessories
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2.5 Amp AC adapter for Celestron telescopes
by Celestron
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Omni 6mm 1.25" Plossl
by Celestron
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$29.95 
Omni 40mm 1.25" Plossl
by Celestron
Quantity:  
$49.95 
  • 70mm aperture achromatic refractor optical tube with fully coated optics, dovetail mounting bar, and 1.25" rack and pinion focuser
  • Altazimuth mount with pan handle for control in altitude and azimuth and locks on both axes
  • 10mm (90X) and 20mm (45X) eyepieces
  • 90° 1.25” star diagonal
  • Red dot illuminated non-magnifying finder
  • Operating instructions
  • TheSky Level 1 CD-ROM software
  • No-tool adjustable height tripod with stainless steel legs and accessory tray.
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Celestron - AstroMaster 70 AZ, 2.8" Altazimuth refractor

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Celestron - AstroMaster 70 AZ, 2.8" Altazimuth refractorFull-length image of scope on tripod.Close-up of the dovetail and locking knob, pan handle, azimuth clutch knob, red dot finder, focuser, star diagonal, and eyepiece.Close-up of the red dot finderr, focuser, star diagonal, and eyepiece.
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The Celestron AstroMaster 70 altazimuth refractor is an economical introduction to casual astronomy and terrestrial nature study for the backyard astronomer. For not much money, it supplies surprisingly good images of nature, the Moon, the planets, and many of the brighter deep space objects . . .





. . . our 34th year