Explore Scientific 5.5mm 100° field waterproof 2" eyepiece


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The Explore Scientific 5.5mm argon-purged waterproof 2" eyepiece combines a high power capability with a 100° apparent field to provide a jaw-dropping observing experience in your telescope.

Our Product #: ES05
Explore Scientific Product #: EPWP10055-01
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Product Description

The 5.5mm 100° field argon-purged Explore Scientific eyepiece is designed to provide a spectacular maximum field/high power image with telescopes having focal ratios as fast as f/4. Its very wide field also makes it convenient for moderate power lunar and planetary observing with Dobsonians, as you have much longer to observe before the planet drifts out of the field and the scope has to be repositioned. That said, it is worth noting that the new 5.5mm Explore Scientific is marvelous for open clusters, nebulas, galaxy clusters, and globular clusters with any telescope capable of using a 2” eyepiece.

The 100° apparent field of this 5.5mm Explore Scientific eyepiece is nearly 50% larger in area than an 82° field eyepiece. You could get a similar true field with a longer focal length (but narrower apparent field) conventional eyepiece, but the 5.5mm Explore Scientific Explore Scientific has the benefits of the higher power and darker sky backgrounds that are inherent in its shorter focal length.

The new 5.5mm Explore Scientific 100° field 2” eyepiece is O-ring sealed and argon-purged to be 100% waterproof. While waterproofing might seem important only for observing underwater, waterproofing serves five useful purposes for the astronomical observer as well.

One, internally sealing the eyepiece and purging it with inert, dry nitrogen gas prevents internal fogging in the eyepiece when observing at very low temperatures. Two, for observers in dusty climates, it halts the intrusion of wind-blown dust and fine particulates into the eyepiece body. Three, for observers in very humid climates, it prevents the growth of fungus on the internal lens elements. Four, for all observers, it maximizes the life of the internal optical coatings. And finally, five, the waterproof 5.5mm Explore Scientific eyepiece is easier to clean, as there is no risk of cleaning solution migrating from the top of the lens and seeping around edges to be trapped in between elements. To insure a perfect seal, Explore Scientific tests every eyepiece in one meter of water for 30 minutes before shipping.

There is a soft rolldown eyecup to shield the eye from ambient light (from a neighbor’s security light, for example) and improve the image contrast. At an eye relief of 12.5mm, the 5.5mm Explore Scientific would normally somewhat vignette the field of view for eyeglass wearers. However, since the 100° field is so wide that you can’t see the full field without having to move your head from side to side to take it all in anyway, vignetting in the conventional sense is not a problem.

The 5.5mm Explore Scientific has high contrast, comfortable eye relief, and full field sharpness – with well-controlled astigmatism, field curvature, and lateral color. The 5.5mm Explore Scientific fits 2" focusers only. A safety groove is machined into the 2" chrome barrel to engage your focuser thumbscrew. This helps prevent the eyepiece from falling should the thumbscrew accidentally loosen while observing.

This individually serial numbered Explore Scientific eyepiece is backed by a limited one year warranty, which will be extended to an Explore Scientific transferable lifetime limited warranty when its warranty card is registered with Explore Scientific within 60 days of purchase.

Tech Details

Warranty 1 year, extendable to lifetime


Review by:
When seeing is good, this is my high power eyepiece for planets. Nice to see Jovian moons when looking at the planet. (Posted on 9/10/2019)
Review by:
I own the 20mm 14mm 9mm and 5.5mm ES 100deg. Excellent for planetary viewing with moons. Wonderful views. (Posted on 12/31/2018)
Review by:
I own the 20mm 14mm 9mm and 5.5mm ES 100deg. This is a great focal length for viewing the planets and their moons. Wonderful views. (Posted on 12/31/2018)
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