Large aperture astronomical binoculars are a sheer joy to use, especially for the larger deep-sky objects, so how does Orion’s new 100mm offering perform?
Pros: Rigid construction, good anti-reflective coatings.
Cons: Poor stray light control, wide effective minimum interpupillary distance (IPD).
The Orion binoculars (MSRP: $399.99), which come in an aluminum case, are of Porro-prism construction and feature individual-eyepiece focusing. In common with many other large binoculars, there is a longitudinal bar that connects the hinge to cuffs on the objective lens cells.
As well as providing overall structural rigidity, the bar carries a sliding mounting post that enables you to achieve perfect balance when you mount it. Unfortunately, at the point of perfect balance, the post restricts the minimum achievable IPD to an unusually wide 66mm; to get less than that, the binoculars must be mounted so that they are front-end heavy.
The internal construction appears robust, with the prisms secured in proper cages, so they should not become dislodged by minor bumps. The insides of the objective tubes are smooth and without light baffles, although they are stepped where the objective tubes join with the objective cells and the prism housings. The result is that stray light is not well controlled, and glare from a first-quarter Moon within about 5° of your field of view becomes intrusive, although the effective anti-reflective coatings almost eliminate spurious ghost images.
Despite those shortcomings, the binoculars are still a pleasure to use. The Great Orion Nebula (M42) was bright and, the longer you look, the more structure and detail you’ll see. The Orion Trapezium Cluster was cleanly split into four stars over the central third of the field of view. Color rendition was very good; the binoculars were tested when Betelgeuse was in its early 2020 dimming phase, when it appeared particularly ruddy.
The Whirlpool Galaxy (M51) revealed both of its core condensations, and the often difficult Pinwheel Galaxy (M101) was easy to see in a suburban sky, despite the galaxy’s relatively low altitude. The binoculars’ real strength, though, is open clusters. The Pleiades were simply stunning and it was enjoyable to compare and contrast the Messier clusters in Auriga and Gemini. However, it was Cassiopeia region of the Milky Way that truly demanded attention, with so many knots and clusters of stars visible in the binoculars that it was easy to become lost.
You will need to consider how you mount these binoculars. At the very least, you will need a sturdy tripod and head, but this combination is never completely satisfactory. Fortunately, Orion sells the binoculars as a “kit” with their very capable Monster parallelogram mount; the two are very well-matched.
This review is adapted from an article published on BBC Sky at Night Magazine: