More Info
Recently, Astronomy magazine ran a "buyer's guide" to portable 4" apochromatic refractors. All were impressive telescopes, no doubt. But considering their price tags, which ranged from $2,695 (yes, that was the cheapest) to $3,595, you'd be excused if you didn't run right out and throw down your credit card for one.
Here's something more practical: Our Orion 100mm ED Apochromatic Refractor Telescope Optical Tube. Priced well under $1,000, it's by far the most jaw-dropping value in high-end refractors ever offered. The extra-low dispension 100 delivers images remarkably free of chromatic aberration, thanks to its fully multi-coated 100mm objective doublet. It's crafted with one element of FPL-53 extra-low dispersion (ED) optical glass from Japan. The 100mm aperture gives it 56% greater light grasp than our ED80, and the 900mm focal length (f/9.0) is ideal for visual planetary and lunar study and excels for imaging work as well.
The baffled, 36"-long aluminum telescope optical tube is outfitted with a 2" Crayford-style focuser for exceptionally smooth focusing with no backlash. It accepts both 2" and 1.25" diagonals. A molded-in dovetail base accepts any Orion finder scope.
The revolution in affordable apochromatic refractors continues with the Orion 100 Extra-Low Dispension Apochromatic Refractor Telescope Optical Tube. Order yours today.
Warranty
Limited Warranty against defects in materials or workmanship for one year from date of purchase. This warranty is for the benefit of the original retail purchaser only. For complete warranty details contact us at 800-676-1343.
Warning
Please note this product was not designed or intended by the manufacturer for use by a child 12 years of age or younger.
Product Support
Visit our product support section for instruction manuals and more
Specs
Best for viewing
Brighter deep sky
Best for imaging
Deep sky
User level
Beginner - Telescopes suited for beginners are easy to use and maintain. Very good optical and mechanical quality. A great first telescope that will show you the moon and planets.Intermediate -Telescopes for the intermediate user are more robust in features and performance. Excellent quality in optics and mechanics, and more complex in use. An intermediate telescope will allow an enthusiast to "grow" in the hobby.
Advanced - Advanced telescopes are high performance, with exceptional quality. They may require more commitment to use in set-up time and technical savvy. Some advanced telescopes are easy-to-use but large and heavy. An advanced telescope is a purchase for a lifetime.
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.
Advanced
Optical design
A small, quality achromatic refractor of 60mm to 80mm aperture makes a fine starter scope for observing the Moon and major planets. They're affordable ($100 to $350), portable, and maintenance-free, all desirable factors if you're just "testing the waters" of Astronomy. If nebulas and galaxies are your main interest, a Newtonian reflector or Schmidt-Cassegrain is the way to go. Moving up to a 90mm or 100mm refractor will snare more objects and provide better performance, for a higher price. Renowned for crisp, sharp images, refractors are the priciest per inch of aperture of all telescope types. A refractor is the scope of choice if you will be doing most of your stargazing from city or suburbs, where the night skies are moderately light-polluted. Since viewing is restricted mostly to the Moon and planets a big scope would only amplify the skyglow, yielding poor washed out images. Reflectors Newtonian reflectors are great all-around scopes, offering generous apertures at affordable prices. They excel for both planetary and deep-sky viewing. Of course, the larger the aperture, the more you'll see. Smaller, 3" and 4.5" equatorially mounted Newtonians will provide a nice "survey" of celestial luminaries, and they maintain their portability. Six-inch and 8" Newts have enough aperture to deliver captivating images of fainter star-clusters, galaxies, and nebulas-especially in a reasonably dark sky. Although the 6" to 8" Newts are bulkier and weigh more, with a Dobsonian mount they are easily manageable by one person making them a wonderful beginner scopes. Dobsonian-mounted reflectors have lower price tags than their equatorial counterparts, starting in the mid-$300s for a 6" Dob. Schmidt-Cassegrains If portability is important to you, you might want to consider a "catadioptric" scope such as a Schmidt-Cassegrain or Maksutov-Cassegrain. They pack a hefty aperture into a very compact tube. An 8" Schmidt-Cassegrain provides excellent views of the Moon, planets, and deep-sky objects, and is well suited for astrophotography. Schmidt-Cassegrains should be considered as an investment priced over $1000 for the most basic 8" models (and hundreds more to outfit it for astrophotography). The Bottom Line Now that you've received the crash course on telescopes, here's some parting advice for aspiring astronomers: Get as much aperture as you can reasonably handle. Big aperture is desirable, however you don't want to end up with a scope that is too big or complicated to conveniently set up, haul around-and use! Also, avoid those gee-whiz, techno-toy scopes with the hefty price tags that are showing up in the big chain stores. For a first telescope, we recommend a basic refractor of 90mm aperture or smaller, or a Newtonian reflector of 6" aperture or less, unless you're really committed. After you've learned the basics of observing and developed an appreciation for the hobby, then you can move up to a bigger, fancier scope.
Refractor
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.
100mm
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.
900mm
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/9.0
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 multi-coated
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
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.
Extra low dispersion FPL-53
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.
1.16arc*sec
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.
16x
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.
200x
Highest theoretical magnification
200x
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
Mount type
Optical Tube without Mount
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.
Lunar, planetary & long exposure
Length of optical tube
36.0 in.
Weight, optical tube
7.0 lbs.
Additional included accessories
Camera adapter
Other features
One element ED glass in apochromatic primary lens, Crayford focuser, Machined aluminum lens cell
In the Box
Orion Apochromatic Refractor optical tube assembly
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
How do I calculate the magnification (power) of a telescope? How do I clean any of the optical lenses?
Reviews
Orion ED100 100mm f/9 Apochromatic Refractor Telescope 7
7
Already have a good mount but want another scope to put on it? Orion's 100mm ED refractor telescope is perfect for the advanced observer or astrophotographer wanting great views at an amazing price. The ED glass provides very low color distortion.
