Orion EON 115 ED Triplet APO Refractor Telescope Review

Whenever you have a tube-only buy, it’s likely you’re investing in a very solid OTA.

What is an OTA?

It’s an Optical Tube or Optical Tube Assemblies that are standalone purchases that do not include a mounting system or tripod. The Orion EON 115 ED is one of those.

So, what you are paying for that justifies a high price without the other much-needed equipment?

The optics.

The EON has an APO triplet optical system that is often desired for quality astro imaging. There’s more to learn, so zoom on in!

Zooming in…

✔️ Best Feature: APO optics

Worst Feature: May require a field flattener

👌 Ideal For: Celestial Viewing, Terrestrial Viewing, Lunar & Planetary Observation, DSO Viewing, Beginners, Intermediates, Experts

  • Optical Design: Refractor
  • Aperture: 115 mm
  • Focal Length: 805 mm
  • Focal Ratio: f/7
  • Eyepieces Included: None

Our Verdict: Without making the leap into the $2000 budget or more, the EON 115 ED Triplet APO telescope allows you to take your astrophotography skills to the next level. As a refractor with appropriate focal specs for imaging, the EON is up to the task and will last for eons as one of your favorite scopes.

Who is the Orion EON 115 ED Triplet APO Best Suited to?

The Orion EON 115 ED APO telescope will be an attractive buy for beginners and intermediates looking for a serious visual scope or an upgrade to further develop astro imaging skills. The price is right within range for those on a budget looking for APO optics as they can easily start in the $2000 price range.

Orion markets the EON as an advanced system, and as a 4.5” APO refractor, it should be recognized by advanced users as an excellent choice for astrophotography because of its versatility. Even then, the EON is very popular with amateurs looking for growth from a telescope that will last a lifetime and intermediates looking for a refractor with APO on budget to expand their imaging catalog.

How Does the Orion EON 115 ED Triplet APO Perform?

The Orion EON 115 has a 4.5” aperture, 805 mm length, and f/7 ratio. It might have a “tiny” aperture for what serious users would consider for deep sky observation, but it’s certainly enough for astrophotography.

Its moderately fast focal specs lend itself to both wide-field views and high-power observation. For visual purposes, the 4.5” aperture works well for visuals on the moon and bright DSOs. However, it will be restrictive on fainter DSOs. Long-exposure, lunar, planetary, solar, and Messier objects for imaging will be within your reach.

With its extra-large 3” Crayford focuser, you have very precise 11:1 dual speed adjustment. It’s also rotatable by two points, so you can keep your knobs parallel to the ground and camera framing where you want it regardless of the tube or focus knob positions. The major factor to consider for astro imaging is the mount. With a Vixen-style dovetail mounting bar, it will fit most any modern Alt-azimuth or equatorial mount available today.

Features & Benefits

APO Optics

Otherwise known as an apochromatic triplet. It’s a series of three lenses that brings three wavelengths to focus at a common focal point. This dramatically reduces CA (Chromatic Aberration) that is easily identified as false color, color bleeding, or color fringing. High contrast targets or bright targets like the moon and Jupiter will maintain their true colors. Without ED (Extra-low dispersion) and APO optics, these objects would be seen with CA that can severely interfere with imaging.

What is ED? ED refers to elements that optical glass can be made with that provides even more aberration-free benefits. Whenever you have an APO lens system, you almost always have ED or FL (Fluorite) elements to improve image quality for either visual or imaging purposes. Improved contrast, sharpness, color fidelity, and resolution is the goal. The Eon 115 has one element ED (FK-61) glass. This is great for most imaging but minimal CA may be noticeable at very high power.

Good for Visual Use

Usually, if you’re buying a telescope with APO optics, you likely have imaging in mind which requires a little more quality in every component than what is needed just for visual use. But, if you prefer to hang out with the scope for casual observation, you’ll have the CA-free benefits of APO and ED optics.

With a 4.5” aperture, you’ll be able to view local objects and bright DSOs like Orion Nebula for example. Unfortunately, it’s still not large enough to gather enough details or light on the dimmest DSOs. While you may get excellent visuals on Jupiter and its satellites, its features are rather faint. But, at least what you can see will have exceptional color fidelity and contrast.

Good for Astrophotography

While you may be tempted to go bigger, remember that there is no substitute for optical quality. In this case, you may have a modest aperture, but you have excellent optics. Refractors are already more expensive per inch in aperture than reflectors, and due to the difficulty in design and the need for color corrective glass elements and coatings required for the optics, maximum size is limited. This obviously is restrictive on very faint DSOs.

However, you may be surprised as to what faint objects you can capture on a refractor of this size. The EON 115 mm has resolution of approximately one arc second that pairs very well with the resolution that is allowed by most atmospheric conditions. The large 3” focuser holds heavy loads suitable for astro imaging. It will allow full-frame imaging sensors a large and full field. The included tube rings have multiple threaded holes to allow piggybacking various astro imaging equipment. Whether you want to do planetary photography with a planetary camera or DSO imaging with a DSLR, the EON will provide stellar photographs.

Mounting Options

Invest in a quality mount. Oftentimes, a serious astrophotographer will spend more on a mount system and it is justified. The mount is what will make or break your efforts in astro imaging. The EON comes with a narrow, long (9.7”) Vixen dovetail mounting bar that is compatible with many different types of mounts.

For imaging, you’ll want a computerized Go To mount. A single-axis or dual-axis motor drive will provide the motorized tracking and slewing. The hand control is what you use to control the functions and access a database that allows you to find objects in the sky.

You’ll want a very sturdy mount made from quality materials that will hold up the weight of the OTA and all additional imaging equipment. Since the OTA weighs approximately 22.5 lbs with the tube rings and dovetail bar attached, and if you were to add another 5-10 lbs for basic gear like a DSLR and 2” eyepiece, you’ll need a high payload capacity mount of 40 lbs or more. This would be something like an EQ6 mount.

Limitations

May Require a Field Flattener

The EON 115 ED APO is what I’d consider a moderately fast telescope with its focal ratio of f/7. While it’s excellent at providing a bit of everything from wide-field viewing to high power observation, it may suffer with field curvature.

To compensate for this inherent flaw in refractor scopes, you may need to purchase a field flattener to improve imaging quality. You’ll likely need to add this accessory as a must-have to your list of extra gear to buy to get completely set up.

Popular Questions

Is the EON 115 ED Triplet APO Portable?

Well, the OTA with its included accessories weighs about 22.5 lbs. It’s a rather heavy rig, but remember you have a refractor telescope with an advanced APO optical system which means more glass and more weight. When you add the type of mount and tripod system that you’d need for astro imaging, you could be looking at a possible total weight of 90+ lbs. If you have the means to transport it, it’s a scope worth taking out to a dark and remote location, but its potential total weight indicates it may be more of a stay-at-home type setup.

Do You Really Need a Field Flattener to Use the Orion EON Telescope?

For visual use, a field flattener is not an essential accessory. For imaging, it’s highly recommended to purchase a field flattener lens to improve image quality and reduce field curvature. However, a camera with an imaging sensor smaller than ASP-C may not produce any difference even with a field flattener.

Does the Orion EON ED APO come with any Accessories?

The EON 115 mm does come with a hard carry case that has a die-cut foam interior. Dimensions: 35” x 10.5” x 11.25”. Standard accessories include a 3” Crayford focuser and two hinged tube rings with threaded holes for mounting other accessories. The Starry Night Special Edition astronomy software digital download insert is also included.

Other than those things, the EON is accessory lacking. There are no eyepieces or diagonal included.

What Type of ED Glass do the Orion EON Telescopes Have?

The Eon series of telescopes have FK-61 ED glass elements in an air-spaced triplet optical system. FK-61 is generally considered first-generation ED glass, is made in China (as is the EON telescope) and is very similar to FPL-51 made in Japan. Color correction with FK-61 is much improved versus non-ED optics, but it’s still entry-level compared to higher grade ED glass. This telescope has one element ED glass.

Conclusion

The Orion EON 115 ED Triplet APO telescope is a buy that you will not be disappointed with.

With a closer examination, it does have some quality features, but is still rather entry-level if you’re comparing ED/FL elements.

Where does it balance out?

The price!

For a refractor with APO optics, it offers excellent value to the budding photographer.

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