*2nd* Orion Observer 70mm Altazimuth Refractor Telescope

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*2nd* Orion Observer 70mm Altazimuth Refractor Telescope

This product is a 'Second'. Learn more

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Item # 79881

Specs

Best for viewing

Lunar & planetary
Best for imaging

Lunar & planetary
User level

User level

Beginner - Suited for a wide range of uses, Level 1 telescopes are simple to operate and set up. Some initial assembly may be required. Very good optical and mechanical quality. Great for families, young people, and folks who don't want to mess with equipment but just want to take a look. Any of these scopes will show you countless lunar craters, Saturn's rings and a myriad of star clusters and nebulas! Referring to the manual is recommended.

Intermediate - These scopes offer higher performance and more advanced features than Level 1 models. They typically take a bit longer to learn and need some set-up or adjustments. But anyone with the slightest technical bent will have no problem getting familiar with these models. Referring to the manual is recommended.

Advanced - These scopes provide the best performance but may require more skill to master and appreciate. They have exceptionally fine optics and mechanics. Some are easy to use but are but on the large or heavy side. Some are intended for specialized uses. These scopes will appeal to the more technically inclined. Referring to the manual is highly recommended.

Expert - Expert telescopes offer uncompromising optical and mechanical quality for the most demanding amateur astronomer. They may be technically involved or designed for specialized use, such as astrophotography or detailed deep sky observation. They carry a premium price, but are designed to provide the ultimate performance in the field. Referring to the manual is highly recommended.

Beginner
Optical design

Optical design

Reflector telescopes use a pair of large and small mirrors to direct incoming light to the eyepiece. Refractor telescopes refract, or "bend" incoming light to a focus by means of an objective lens. Cassegrain telescopes, such as Maksutov-Cassegrains, "fold" incoming light using two mirrors and a front "corrector" lens.

Refractors
Optical diameter

Optical diameter

The optical diameter (also known as aperture), is the size of the telescope's main light collecting lens or mirror, measured in millimeters or inches. As the diameter increases, more light is collected and the resolution increases.

70mm
Focal length

Focal length

The focal ratio of an optical system is the ratio of a telescope's focal length to its aperture. Short focal ratios (f/5, f/4.5) produce wide fields of view and small image scales, while long focal lengths produce narrower fields of views and larger image scales.

700mm
Focal ratio

Focal ratio

The focal ratio of an optical system is the ratio of a telescope's focal length to its aperture. Short focal ratios (f/5, f/4.5) produce wide fields of view and small image scales, while long focal lengths produce narrower fields of views and larger image scales.

f/10.0
Coatings

Coatings

Lenses are coated with an antireflective material to ensure that as little light as possible is reflected away, so more gets to your eye. Good lenses are at least "fully coated," with a single layer of magnesium fluoride applied to each air-to-glass lens surface. Multiple layers of coatings are even more effective; the term "multi-coated" means one or more lens surfaces have multiple coatings. "Fully multi-coated" is even better, meaning that all lens surfaces are multiple-layer coated. Mirror star diagonals are coated with a reflective material similar to telescope mirrors in order to reflect the light into the eyepiece. Standard aluminum coatings reflect between 88%-92%, and enhanced aluminum reflects 97%. Dielectric coatings use a different process to deposit a coating that reflects 99% of the light. In addition to the higher reflectivity, Dielectric coatings are much more durable than aluminum coatings, so they last longer and can be cleaned with less risk of damage.

Fully coated
Optics type

Optics type

Newtonian reflectors will have either a spherical shaped mirror, which is less expensive to produce, or a higher quality parabola, which does not result in spherical aberration. Cassegrain telescopes routinely use spheres in addition to other lenses in the optical path to correct for residual spherical aberration. Refractors use a series of lenses to provide a clear image. Designs range from a standard air-spaced doublet (two lenses in a row) to exotic designs such as oil-spaced triplets and 4-element multi group lenses.

Air-spaced doublet
Glass material

Glass material

Refractors use glass lenses to focus the light, and the glass material plays an important role in the quality of the resulting image. Standard achromatic refractors routinely use Crown and Flint for the two elements, but more expensive apochromatic refractors can use ED (extra low dispersion) glass for one or more of the lenses. Reflector mirrors are made from glass with different levels of thermal expansion. Standard mirrors are made from material such as Soda-Lime Plate glass and BK-7 glass. Glass with Pyrex or other low thermal expansion material will not change shape as dramatically during the cool-down period, resulting in more stable images during this period.

Crown/Flint
Eyepieces

Explorer II 25.0mm, 10.0mm
Magnification with included eyepieces

28x, 70x
Resolving power

Resolving power

The theoretical resolving power of a telescope can be calculated with the following formula: Resolving power (in arc seconds) = 4.56 divided by aperture of telescope (in inches). In metric units, this is: Resolving power (in arc seconds) = 116 divided by aperture of telescope (in millimeters). Note that the formula is independent of the telescope type or model, and is based only upon the aperture of the telescope. So the larger the telescope's aperture, the more it is capable of resolving. This is important to keep in mind when observing astronomical objects which require high resolution for best viewing, such as planets and double stars. However, it is usually atmospheric seeing conditions (not the telescope) which limits the actual resolving power on a given night; rarely is resolution less than one arc-second possible from even the best viewing locations on Earth.

1.65arc*sec
Lowest useful magnification

Lowest useful magnification

Lowest useful magnification is the power at which the exit pupil becomes 7mm in diameter. Powers below this can still be reached with the telescope to give wider fields of view, but the image no longer becomes brighter at a lower power. This is due to the fact that the exit pupil of the telescope (the beam of light exiting the eyepiece) is now larger than the average person's dark adapted pupil, and no more light can fit into the eye.

10x
Highest useful magnification

Highest useful magnification

The highest practical limit is different from the often used "highest theoretical magnification" specification. The "theoretical" limit generally is 50x the aperture of the scope in inches (2x the aperture in mm). So for example, an 80mm refractor is capable of 160x, and a 10" telescope is theoretically capable of 500x magnification. But after approximately 300x, theory breaks down and real world problems take over. The atmosphere above us is constantly in motion, and it will distort the image seen through the telescope. This effect may not be noticeable at lower powers, but at higher powers the atmosphere will dramatically blur the object, reducing the quality of the image. On a good night (a night where the air above is steady and the stars aren't twinkling), the practical upper limit of a large telescope is 300x, even thought the theoretical limit may be much higher. This doesn't mean the scope will never be able to reach those higher "theoretical" powers - there will be that rare night where the atmosphere is perfectly still and the scope can be pushed past it's practical limit, but those nights will be few and far between.

140x
Highest theoretical magnification

140x
Limiting stellar magnitude

Limiting stellar magnitude

The limiting stellar magnitude is a measure of the faintest star you can see through the telescope.

11.9
Optical quality

Optical quality

"Diffraction Limited" means that the limits of image detail are determined by the physical properties of light, and not by optical defects in the telescope.

Diffraction Limited
Finder scope

EZ Finder II
Focuser

1.25" Rack-and-pinion
Diagonal degrees

1.25" 90° Mirror Star
Mirror coatings/over-coatings

Magnesium Flouride
Mount type

Altazimuth
Astro-imaging capability

Astro-imaging capability

The astro-photographic capability of the telescope is based on the style, stability, and accuracy of the mount and tripod. Telescopes on either very lightweight mounts or non tracking mounts (such as Dobsonians) are capable of only very short exposures such as lunar photographs. If a motor drive is attached to an equatorial mount, even a small lightweight mount is capable of capturing some planetary detail. Larger EQ mounts that utilize very precise tracking and excellent stability are capable of longer exposure deep-sky photography.

Simple moon shots
Computerized compatibility

Computerized compatibility

Some mounts are compatible with a motorized Go-To system for fully automated computer finding of objects in the night sky. Others mounts are compatible with computer finding systems which require the user to manually move the mount to the object's position as indicated by the computer finder.

Not compatible
Tube material

Aluminum
Tripod material

Aluminum
Height range of mount

Height range of mount

The height range specification is a measure of the tripod itself - not the eyepiece height. Since telescopes come in all shapes and sizes, the eyepiece height will vary, even when using the same tripod. For an EQ tripod the mount is set up so the counterweight shaft is horizontal, and then the height is measured from the ground to the center of the mounting plate.

29.50 in. - 50.00 in.
Length of optical tube

27.7 in.
Weight, fully assembled

6.5 lbs.
Additional included accessories

Other included items are not always the same between a new and a second. Seconds may be older versions of the new product, or may be customer returns where accessory substitutions have been made.
Other features

2nds are covered by Orion's Satisfaction Guarantee
Warranty

One year

Shipping Info

Orders received by noon Pacific Time for in-stock items ship the same business day. Orders received after noon will ship the next business day. When an item is not in-stock we will ship it as soon as it becomes available. Typically in-stock items will ship first and backordered items will follow as soon as they are available. You have the option in check out to request that your order ship complete, if you'd prefer.

A per-item shipping charge (in addition to the standard shipping and handling charge) applies to this product due to its size and weight. This charge varies based on the shipping method.

Standard Delivery: $0.00
3 Day Delivery: $32.00
2 Day Delivery: $32.00
Next Day Delivery: $39.00

Reviews

Why Buy From Orion

Beginner

User level

Optical design

Optical diameter

Focal length

Focal ratio

Coatings

Optics type

Glass material

Resolving power

Lowest useful magnification

Highest useful magnification

Limiting stellar magnitude

Optical quality

Astro-imaging capability

Computerized compatibility

Height range of mount

Why Buy From Orion

Shop Our Catalogs

About Orion Telescopes & Binoculars

Why Buy From Orion

Beginner

User level

Optical design

Optical diameter

Focal length

Focal ratio

Coatings

Optics type

Glass material

Resolving power

Lowest useful magnification

Highest useful magnification

Limiting stellar magnitude

Optical quality

Astro-imaging capability

Computerized compatibility

Height range of mount

Why Buy From Orion

Why Buy From Orion

Shop Our Catalogs

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About Orion Telescopes & Binoculars