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Orion Explorer II Eyepieces

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In the interest of full disclosure, I have no financial stake in any of the companies mentioned in the following article.

Discontinued only recently, Orion’s “Explorer II” series of eyepieces served for more than a decade as their “bargain” eyepieces for beginners or astronomers on a budget. Listed in the catalog as “3 and 4 element designs,” the Explorer II line was a combination of Kellners and Plössls. The eyepieces were available in focal lengths of 25, 20, 17, 13, 10 and 6 millimeters. In earlier sets, the 25mm and 10mm oculars were Kellners while the rest were Plössls. In later sets, only the 25mm eyepiece was a Kellner. All eyepieces (including the Kellners!) had a 50 degree apparent FOV, had fully coated optics and blackened lens edges. For (typically) around $27 each, they were downright cheap. How were they as eyepieces?

In 1998 I purchased the 25mm, 17mm and 10mm Explorer IIs as part of an accessory package to a 6” Deep Space Explorer Dobsonian. These were from the earlier line, so the only Plössl in the set is the 17mm. The build quality of these eyepieces is excellent. The overall fit and finish is very nice, made of beefy anodized aluminum. The eyepieces do not include rubber eyecups, but these can easily be added later. AR coatings consist of a single magnesium fluoride layer on each glass surface, but no surfaces are left uncoated. The filter threads are solid, and have not worn down at all even after 11 years of frequent use.

Each of the 3 eyepieces provides very good views, with the 17mm being the best of the three (not surprisingly). The two Kellners, however, are of surprisingly good optical quality. Each one has an apparent FOV equal to a Plössl, and each provides a very decent, crisp image with sharpness over a surprisingly large portion of the FOV. Optically, the Explorer IIs are staggeringly good performers in spite of their low cost. While higher-end Plössls and Orthoscopics will still walk all over them, they do provide an incredible bargain for the price. They also make very good “Star Party” eyepieces, as their low cost makes slightly more dispensable in case a careless member of the general public accidentally damages one while still giving people really nice views.

Although they have been discontinued, they pop up on the used market quite a bit at even lower prices than originally sold for. I highly recommend them, as they give an enormous amount of bang for the buck.

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