The Orion Observer 70mm Altazimuth was a compact 70mm f/10 refractor designed primarily for beginning astronomers. Its simple altazimuth mount, relatively light weight and included eyepieces made it possible to start observing without the additional setup associated with larger or more complicated telescopes.
The Observer 70mm AZ has since been discontinued by Orion. This review is retained as a reference for readers researching the telescope second-hand or looking for information about this older model.
With a 70mm aperture and 700mm focal length, it was primarily intended for observing the Moon, planets and brighter deep-sky objects. Its relatively small aperture also places clear limits on what can be expected from faint targets.
70mm f/10 Refractor Optics
The Observer uses a 70mm achromatic objective with a 700mm focal length, giving it a focal ratio of f/10. Its relatively long focal length is useful in a beginner refractor because it helps control the chromatic aberration that can produce colored fringes around bright objects, although it does not eliminate it completely.
The 70mm aperture provides substantially more light-gathering ability than the naked eye while keeping the telescope compact and inexpensive. Combined with the relatively long focal length, it represents a conventional design for a small beginner refractor.
Orion supplied 25mm and 10mm eyepieces, providing magnifications of 28× and 70× respectively. The lower power is useful for locating objects and viewing larger targets, while 70× provides more image scale for the Moon and planets.
Simple Altazimuth Mount for Beginners
The Observer 70mm uses a simple altazimuth mount, allowing the telescope to move up and down in altitude and from side to side in azimuth. This makes it more intuitive for a beginner than an equatorial mount, with no polar alignment required before observing.
The mount also includes a fine altitude adjustment, which helps make small vertical movements when centering or following an object. An EZ Finder II reflex sight was supplied with the telescope to help point the main optical tube toward objects visible to the naked eye.
The complete telescope weighs only around 5.7 lb (2.6 kg), making it easy to carry outside as a complete setup. That portability is useful for beginners because the telescope requires relatively little preparation before an observing session can begin.
What Can You See Through It?
The Moon is the Observer 70mm’s strongest target, with its larger craters, mountain ranges and the changing shadows along the terminator readily visible. The 70mm aperture also provides enough resolution for useful views of the brighter planets when atmospheric conditions are favorable.
Jupiter’s four Galilean moons are easily within reach, along with the planet’s two main cloud belts under good conditions. Saturn’s rings can be clearly distinguished from the planet itself, while Venus shows its changing phases. Mars is a more challenging target, with significant surface detail generally requiring favorable conditions and a close approach to Earth.
Beyond the Solar System, the telescope is best suited to bright open clusters, double stars and the brightest deep-sky objects. Targets such as the Pleiades, Beehive Cluster and Orion Nebula are accessible, while faint galaxies and nebulae remain much more demanding, particularly from light-polluted locations.
Limitations to Consider
The Observer 70mm’s main limitation is its 70mm aperture. It performs well on bright targets, but it collects considerably less light than larger beginner telescopes, limiting what can be seen in faint galaxies, nebulae and other deep-sky objects.
As an achromatic refractor, it can also show some chromatic aberration around particularly bright targets. The relatively long f/10 focal ratio helps keep this under control, but observers may still notice colored fringes around objects such as the Moon, Venus and Jupiter.
The simple altazimuth mount is easy to use, but it is designed primarily for visual observing rather than astrophotography. It also requires the observer to move the telescope manually as objects drift across the field of view due to Earth’s rotation.
These limitations are typical of a small beginner refractor rather than unusual faults with the Observer 70mm. Its strength lies in providing a simple, portable way to explore brighter objects in the night sky, rather than delivering the light-gathering ability or tracking capabilities of a larger and more advanced telescope.
Who Is the Orion Observer 70mm Best For?
The Orion Observer 70mm is best suited to observers looking for a simple, lightweight refractor for the Moon, bright planets and brighter star clusters. Its manual altazimuth mount and modest 70mm aperture make it less suitable for observers wanting computerized object finding, automatic tracking or stronger deep-sky performance, but its straightforward design makes it easy to set up, move and use for casual observing.
Specifications
- Optical Design: Achromatic refractor
- Aperture: 70mm
- Focal Length: 700mm
- Focal Ratio: f/10
- Objective Coatings: Multi-coated
- Focuser: 1.25-inch rack-and-pinion
- Mount: Altazimuth
- Finder: EZ Finder II reflex sight
- Included Eyepieces: 25mm and 10mm
- Included Magnifications: 28× and 70×
- Diagonal: 90° mirror diagonal
- Assembled Weight: approximately 5.7 lb (2.6 kg)