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Review - Explore Scientific 2" 17mm & 12mm 92° eyepieces

Posted: 19 September 2020

2" 17mm 92° eyepiece
2" 12mm 92° eyepiece
Explore Scientific
$550 each

In Astronomy Technology Today, Issue 6, June 2020, I reviewed the Explore Scientific 2" 14mm 100° and 2" 5.5mm 100° eyepieces. The review is also available here. This review will discuss the Explore Scientific 2" 17mm 92° and 2" 12mm 92° eyepieces that Explore Scientific provided.

The 92° eyepieces come in lovely boxes that protect the eyepiece during shipment. As I mentioned in the review of the 100° eyepieces, I love the star chart design used on the Explore Scientific product boxes. A nice cloth bag and a warranty card are included. The eyepieces are waterproof (Argon-purged). Explore Scientific provides a fully transferrable unlimited lifetime warranty on waterproof eyepieces, if registered within 60 days of purchase, with anytime free service and repurposing of an eyepiece that is returned for their trade-up program.


The sizes of the two eyepieces are nearly identical, although they are not parfocal with each other.


The next photograph shows the size comparison for the Explore Scientific 92° eyepieces, Explore Scientific 100° eyepieces, and two comparable focal length 1.25" eyepieces.


The eyepieces have a 92° apparent field-of-view. I measured the actual field-of-view of both eyepieces when used on my 12" f/8 (focal length 2438mm) telescope:

2" 17mm 92° eyepiece: 32 arc min
2" 12mm 92° eyepiece: 21 arc min

Both eyepieces have a long eye relief (20mm), which is good for visual observing. However, I could not see the entire wide field-of-view while wearing glasses. The long eye relief makes afocal imaging through the eyepieces a challenge using telescopes with a large secondary mirror, as seen in this image taken with a handheld smartphone using the 17mm eyepiece.


With the 17mm eyepiece the Full Moon's entire disk was visible, giving a large bright view. At the time of Full Moon there were many mountains visible rising above the lunar limb. The sharp view and high magnification really made these lunar features stand out. The top image below taken shortly before Full Moon through the 17mm eyepiece using a handheld smartphone shows nice details, although it was not possible to photograph the entire field-of-view of the eyepiece. The 12mm eyepiece provided a nice bright higher magnification view of the Moon. The bottom image is a similar view through the 12mm eyepiece using a handheld smartphone, but again it was not possible to photograph the entire field-of-view of the 12mm eyepiece.


The 17mm and 12mm eyepieces provided nice views of the planet Jupiter, its Great Red Spot (more a Little Pink Spot), and the four Galilean Moons widely spread out across the entire field-of-view. The combination of high magnifications and wide fields made the view impressive in both eyepieces. Saturn and its Ring system were crisp with several moons visible. The Cassini Division was clearly seen with both eyepieces. The wide field is somewhat wasted when viewing planets, but the long eye relief will be appreciated by those who wear glasses.

The tube diameter for both the 17mm and 12mm eyepieces (2.9 inches and 2.8 inches, respectively) is too large for most smartphone adapters. I was able to take these handheld afocal photographs (single frame, not stacked) of Jupiter and Saturn using an iPhone. The top two images (cropped) show Jupiter through the 17mm and 12mm eyepieces, respectively, and the bottom two images (cropped) show Saturn with the 17mm and 12mm, respectively. (Seeing was not good when I was photographing Saturn.)


From my dark site I enjoy observing galaxies, nebulae, globular clusters, and open star clusters. During the time I had the eyepieces for this review I viewed the galaxies M85 and NGC4457. I had my first visual sighting of Supernova 2020nlb in M85 and Supernova 2020nvb in NGC4457 using the 17mm eyepiece. The galaxies and both supernovae were very distinct in both eyepieces. The bright fields of view and the high magnifications made visually separating the supernovae from the galaxies easy. M57 (Ring Nebula) was a lovely bright view showing its context in the wide field view of the stars. M13 (Great Globular Cluster in Hercules), M4 (globular cluster), and M22 (globular cluster) were impressive in both eyepieces with many of the clusters' stars visible. M16 (Eagle Nebula) showed the nebula faintly visible with a nice view of the nearby star cluster in both eyepieces. M8 (Lagoon Nebula) was gorgeous. M20 (Trifid Nebula) showed the structure of the nebula. M17 (Swan Nebula) was very nice with lots of details visible. The best view of all of these Deep Sky Objects was with the 17mm eyepiece, although the globular clusters tolerated the higher magnification of the 12mm very well.


While the 17mm and 12mm 92° eyepieces make nice additions to your eyepiece collection for lunar and planetary observing, viewing Deep Sky Objects with both of these wide field eyepieces will provide years of observing pleasure. Objects in both eyepieces are very sharp and bright all the way to the edge of the wide field-of-view. These large eyepieces are heavy so be certain your telescope and mount can handle the weight. The high quality 2" long eye relief eyepieces have higher prices than comparable focal length narrow field-of-view eyepieces. The Explore Scientific 2" 17mm 92° eyepiece is $550 (USD) and the Explore Scientific 2" 12mm 92° eyepiece is also $550 (USD). With the Explore Scientific unlimited lifetime warranty your purchase will be protected.

Which lines of Explore Scientific eyepieces is best, 92° or 100°? Since the apparent field-of-view is similar and the prices are comparable for both, it could come down to deciding which focal length is best for your observing (unless you need the long eye relief with the 92° eyepieces). Either way, you will be happy with your decision.

This review appeared in Astronomy Technology Today magazine, Volume 14, Issue 8.

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