2" 14mm 100° eyepiece
2" 5.5mm 100° eyepiece
Explore Scientific
$550, $450

In November 2012 I purchased an Explore Scientific 2" 9mm 100° eyepiece and it quickly became my favorite high magnification eyepiece on my 8" telescope and then my 12" telescope. I had always planned to get another Explore Scientific 100° eyepiece but somehow never got around to it. When Explore Scientific and Astronomy Technology Today offered me the opportunity to review some products for the magazine, I knew that I needed to review other eyepieces in the Explore Scientific 100° line so that more amateur astronomers would want to experience the joy of observing with these very wide field eyepieces. [Note: Explore Scientific provided the 14mm and 5.5mm eyepieces for this review that was first published in Astronomy Technology Today magazine.]

The 100° eyepieces come in lovely boxes that protect the eyepiece during shipment (seen at the right). I love the star chart design used on the Explore Scientific product boxes. A nice cloth bag and a warranty card are included. 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.

As seen below, the 2" 5.5mm 100° eyepiece has nearly the same shape and size as the 2" 9mm 100° eyepiece and the 2" 14mm 100° eyepiece is slightly taller and wider. My 9mm waterproof eyepiece is Nitrogen-purged, whereas the 5.5mm and 14mm are Argon-purged.

The next photos show the size comparison with 1.25" 15mm and 5.5mm focal length eyepieces that I have used for many years. The 2" wide angle eyepieces are significantly larger and heavier than the 1.25" eyepieces. Be certain your telescope mount can handle the extra weight.

First Light with the Explore Scientific 2" 14mm 100° eyepiece and the 2" 5.5mm 100° eyepiece was on the planet Venus using my 12" f/8 telescope. Venus showed a nice thin crescent phase. The 14mm eyepiece gave a magnification of 174X and the 5.5mm eyepiece 443X. The view through both eyepieces was very good and was wider and brighter than the views through my 1.25" eyepieces with comparable magnifications. The 14mm eyepiece had longer eye relief than the 5.5mm. I could easily see the entire wide field-of-view in the 14mm eyepiece, but I had to look sideways to see the 5.5mm field edges. Both eyepieces are nearly parfocal with each other. All three of my Explore Scientific 2" 100° eyepieces show crisp details all the way to the edge of their field-of-view. With such a wide field that is a major design and manufacturing accomplishment.

The eyepieces have a 100° 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" 14mm 100° eyepiece: 31 arc min (think Moon's entire disk being visible at high magnification!)
2" 5.5mm 100° eyepiece: 11 arc min

I viewed several galaxies, nebulae, open star clusters, and globular clusters using the 14mm eyepiece. M51 (Whirlpool Galaxy), 174X, was the best view I have ever had; the spiral arms were very distinct. The globular cluster Omega Centauri, which appears very low in my southern sky, was an incredible sight with this high magnification and wide field view.

The Moon with the 2" 14mm 100° eyepiece was a sharper and more expanded view than with a comparable 1.25" focal length eyepiece. With the wide field-of-view I could see the Moon's entire disk at this medium magnification. That was impressive.

When using a 1.25" 5.5mm eyepiece I have always felt cramped when viewing the Moon. That is not the case with the 2" 5.5mm 100° eyepiece. I could easily take in more sights on the lunar surface using a high magnification.

The comparison photographs below were taken with an iPhone to show the field-of-view differences when using comparable focal length eyepieces. (Note: the phone camera was not able to capture the entire field-of-view with either 100° eyepiece.)

Summary

Looking through the Explore Scientific 2" 100° eyepieces after using 68° and 80° apparent field-of-view eyepieces for decades is like switching to High Definition (16:9) TV from Standard Definition (4:3) TV. You feel more immersed in the scene, especially when viewing the Moon.

The Explore Scientific 2" 14mm 100° eyepiece quickly became the preferred medium magnification eyepiece on my 12" telescope. Its wide field view is so clear and bright that viewing even faint Deep Sky Objects are a joy with this eyepiece. Open star cluster lovers will appreciate the wide field-of-view. Galaxy lovers will enjoy using this eyepiece with its bright wide views. The only drawback for me with this large diameter 2" eyepiece is that none of my smartphone adapters that support 2" eyepieces will fit it properly without significantly reducing the field-of-view seen by the camera. (My hunt is now on for a new smartphone adapter!)

The Explore Scientific 2" 5.5mm 100° eyepiece is great for viewing planets and the Moon. The bright wide field is especially useful for lunar viewing at high magnification. This year's Mars apparition should provide a showcase object for this high magnification eyepiece.

As expected for these high quality 2" wide field eyepieces, the prices are higher than comparable focal length narrow field-of-view eyepieces. Currently, the Explore Scientific 2" 14mm 100° eyepiece is $550 (USD), the Explore Scientific 2" 9mm 100° eyepiece is also $550, and the Explore Scientific 2" 5.5mm 100° eyepiece is $450. But for serious visual observers of the Moon, planets, and Deep Sky Objects the views will be worth it. With the Explore Scientific unlimited lifetime warranty your purchase will be protected.

This review appeared in Astronomy Technology Today magazine, Volume 14, Issue 6.

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