Celestron AstroMaster LT 70AZ Telescope

What the AstroMaster LT 70AZ Is

The AstroMaster LT 70AZ is a 70mm (2.76") f/10 refractor on a light manual alt-azimuth mount. Celestron pitches the LT series at anyone looking for a portable, easy to assemble telescope, and the whole kit weighs 7.2 lbs (3.27 kg).

It is a manual telescope with no computer, so you find objects yourself with the finderscope, a star map or an app.

Refractor Optics

The AstroMaster LT 70AZ is a refractor with fully coated optics. The 70mm (2.76") aperture and 700mm (28") focal length (f/10) gather 100x more light than the human eye. The limiting stellar magnitude is 11.7 and the resolution 1.99 arc seconds (Rayleigh) or 1.66 arc seconds (Dawes). Highest useful magnification is 165x, and the lowest is 10x.

The aluminum tube is 485mm (19.1") long. It attaches with a CG-5 dovetail bar.

The Alt-Azimuth Mount

The manual alt-azimuth mount moves up and down and left and right, the way you naturally point. The pan handle Alt-Az control with clutch gives smooth and accurate pointing: turn the whole panning handle counterclockwise to loosen the altitude clutch, move the telescope, and turn it clockwise to lock. The left and right axis spins freely and does not lock, but the azimuth tension knob on top of the mount sets how stiffly it turns, clockwise to tighten.

Tripod, Assembly and Weights

The tripod has 1.25" steel legs and an accessory tray on its center brace. The height adjusts from 32" to 51" (812.8mm to 1295.4mm) with the mount. The tube weighs 2.5 lbs (1.13 kg) and the complete kit 7.2 lbs (3.27 kg).

The mount and tripod come fully assembled. Extend the legs with the knobs at their base, stand the tripod up and spread the legs until the center brace snaps into place, then twist the accessory tray onto the brace until its tabs lock. With the mounting platform level and the altitude clutch locked, slide the dovetail bar under the tube into the clamp on top of the mount and tighten the large hand knob.

Eyepieces, Diagonal and Finderscope

Two 1.25" eyepieces are included: the 20mm gives 35x for finding objects and wider views, and the 10mm gives 70x for a closer look. Magnification is the telescope's focal length divided by the eyepiece's focal length. The manual suggests finding and centering an object with the 20mm eyepiece first, then changing to the 10mm to zoom in, and notes that more eyepieces can be bought to change the magnification.

The star diagonal goes into the back of the focuser and uses a small mirror to turn the light at a 90 degree angle, for a more comfortable viewing position. Without it the image would be upside down and mirror reversed; the manual says the diagonal flips it right-side up, but it still appears mirror reversed left to right, which is normal for astronomical telescopes.

Align the StarPointer red dot finderscope once, in daylight: pick an easily recognizable object such as a streetlight, a car license plate or a sign, as far away as possible and at least a quarter mile off. Center it in the 20mm eyepiece, turn the finder's power dial all the way up, and without moving the telescope use its two adjustment knobs until the red dot sits on the same object. It should not need realigning unless it is bumped, dropped or removed. Before first use, pull out the small plastic tab under the battery cover, and turn the red dot off when you are not using it to save the battery.

What You Can Observe

The AstroMaster LT series produces bright, clear images of the Moon and planets, and you can observe the belts and moons of Jupiter and the rings of Saturn. It has limits too: for brighter deep space objects like galaxies and nebulae, the larger aperture and light-gathering ability of a Newtonian reflector is recommended.

Try the Moon for your first night: the best time is from two days after New Moon to a few days before Full Moon, when the craters and lunar mountain ranges show the most detail. Put the red dot on the Moon, focus in the 20mm eyepiece, then swap to the 10mm for a much larger view; you may need to refocus when you change eyepieces.

The manual is frank about deep-sky objects: nebulae and galaxies can be large but are very faint, and the vivid reds and blues in photographs come from long exposures; they are not visible in the eyepiece, because the eye is most sensitive to green. Darker skies, away from city lights, make the biggest difference.

Getting the Best Views

Sky conditions matter as much as the telescope. When stars twinkle or flash colours the air is unsteady, so use low power and look for brighter objects; when they shine steadily, the Moon and planets take higher magnification well. Humidity, smoke or haze dim faint objects, and city sky glow can hide them, while the Moon and planets are bright enough to be little affected.

For the best views, the manual suggests setting up on dirt or grass rather than a deck or concrete, which pass vibrations to the telescope; staying out of the direct path of streetlights and house lights; avoiding objects within 5 to 10 degrees over a roof, which radiates the day's heat; and never observing through a window, open or closed. Objects look best near the meridian, where they are highest, and the air is often steadier later in the night than just after sunset.

The manual says a telescope needs at least 10 minutes to cool to the outside air temperature, longer if the difference is large, to minimize heat wave distortion inside the tube. Your eyes take about 30 minutes to adapt fully to the dark, so use a red LED flashlight on its lowest setting and avoid white lights. Observe with both eyes open to avoid fatigue, and for a faint object look slightly to the side of it rather than straight at it.

For finding your way, the manual recommends a red flashlight, a planisphere (a rotating star map set to your date and time), a star atlas, or an astronomy app or computer program. Its star hopping method uses the StarPointer's field as a ruler on the atlas to step from bright stars to fainter targets.

Photographing the Moon and Planets

The manual says the telescope can image the Moon and planets, while deep-sky objects need a more advanced telescope and a mount with finely geared motorized tracking. The simplest method is holding a phone or a point-and-shoot camera up to the eyepiece, which is easier with the low-power eyepiece and a steady hand. Celestron also offers T-adapters and T-rings to use a DSLR body in place of the eyepiece, and planetary cameras that record video on a laptop and stack the frames into a sharper image; these are sold separately.

Care

To clean the optics, remove large particles with a camel hair brush, blow away loose debris with a squeeze bulb or a few seconds of canned air held upright and at an angle, then use a 50/50 mix of isopropyl alcohol and distilled water on white unscented tissue, with low-pressure strokes from the center outward like the spokes of a wheel, never in circles. Dew can be cleared with a hair dryer on low or by pointing the telescope at the ground until it evaporates. Replace the covers after every session, since the tube is not sealed; internal cleaning and adjustments should be done only by Celestron's repair department.

Software

Starry Night Basic Edition software and the SkyPortal app come with the AstroMaster. Starry Night is a way to learn about the night sky and plan observing sessions, and you don't need it to use the telescope.