Explore Scientific 40mm 68° field argon-purged waterproof 2" eyepiece


Availability: More on the way

If you have room in your observing kit for only one long focal length wide angle eyepiece, this Explore Scientific 40mm argon-purged eyepiece may well be the one eyepiece for you.
Our Product #: ES6840A
Explore Scientific Product #: EPWP6840-01
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Product Description

This new 68° 40mm Explore Scientific is a high-quality and physically-impressive low power wide field 2" eyepiece for the serious deep space explorer. It comes with an unusual benefit. It is O-ring sealed and argon-purged to be 100% waterproof. This prevents internal fogging in the eyepiece; keeps the interior dust-and fungus-free; and makes it easier to clean, as there is no risk of excess cleaning solution getting trapped between the lenses.

Many observers feel that a 68° field eyepiece like this Explore Scientific hits the "sweet spot" between the affordable, but "looking down a tube" view of conventional 45°-50° field eyepieces, and the full-immersion, but very expensive, observing experience of an ultra-wide field 82° or 100° eyepiece.

Because of its long focal length, the 2" 40mm Explore Scientific is at its best with telescopes having a focal ratio of f/6 or longer (an f/6 scope gives it a 6.67mm exit pupil, about the largest most observers can fully utilize). A shorter focal ratio will waste some of your scope's light gathering capacity when used with the 40mm Explore Scientific. If your scope's focal ratio is f/6 or above, however, this wide field eyepiece can give you some truly excellent "big picture" views of deep space. It is ideal for observing galaxy clusters, large emission and reflection nebulas, and nebula remnants - no matter what your telescope type, as long as your telescope has a focal ratio of f/6 and longer. You can use the calculator in the "formula" tabe above to see just how wide the field will be with your particular scope.

With a huge 31mm of usable eye relief, the six lens/fully multicoated 40mm Explore Scientific can be used by eyeglass wearers with no vignetting of the field. The eyepiece has a soft fold-down rubber eyecup and comes with dust covers for both ends of the eyepiece.

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. Here's a link to the full details on this unique transferable lifetime warranty

Tech Details

Barrel Size 2"
Eye Relief 31mm
Field of view 68
Focal Length 40mm
Number of optical elements 6
Weight 34.4 oz
Warranty 1 year, extendable to lifetime


Review by:
The 40mm is the first eyepiece on the scope for the wide field views. It does not disappoint. A lot of times after going down to the 7mm the ES40MM is put back for the last looks of the night. Great wide field eyepiece.
(Posted on 12/2/2018)
Review by:
I replaced a less well corrected 40mm eyepiece with this ES68 40mm and got excellent edge-to-edge performance at reasonable cost. I am very happy with it and have zero plans to replace the ES68 40mm. Highly recommended. (Posted on 10/30/2018)
Review by:
Excellent wide view lens. Explore Scientific makes great quality products. (Posted on 10/7/2018)
Review by:
Great eyepiece. Pinpoint stars out to at least 95% of the lens. And the last 5% is still quite manageable. Built to last, high quality materials. Fog/waterproof is also a nice touch, very handy. I will always look to Explore Scientific for great products and deals now. Nice protective case as well very secure. Highly Recommended. (Posted on 8/4/2017)
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