Explore Scientific 25mm 100° field argon-purged waterproof 2" eyepiece


Availability: In stock

The 100° apparent field of this Explore Scientific first-of-its-kind 25mm argon-purged waterproof 2" eyepiece provides superb maximum field/medium power observing in all scopes, from small apo refractors to the largest Dobsonians and catadioptrics.
Our Product #: ES25
Explore Scientific Product #: EPWP10025-01
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Product Description

The new 25mm Explore Scientific 100° field 2" eyepiece is O-ring sealed and argon-purged to be 100% waterproof. To insure a perfect seal, Explore Scientific tests every eyepiece in one meter of water for 30 minutes before shipping.

Internally sealing the eyepiece and purging it with inert, dry argon gas prevents internal fogging in the eyepiece when observing at sub-freezing temperatures. For observers in dusty climates, sealing keeps wind-blown dust and fine particulates from getting into the eyepiece body. For observers in very humid climates, sealing prevents the growth of fungus on the internal lens elements. For all observers, complete sealing maximizes the life of the internal optical coatings and makes the eyepiece 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.

The 25mm Explore Scientific eyepiece has high contrast, comfortable eye relief, and full field sharpness - with well-controlled astigmatism, field curvature, and lateral color. Its optical system (using lenses of dense crown, light crown, dense flint, and lanthanum rare earth optical glasses) is designed for maximum field/medium power deep space use with telescopes having focal ratios down as low as f/4. It is exceptionally effective on nebulas with fast f/ratio reflectors, such as Dobsonians, as it gives both an immense field and a bright exit pupil (over 5.5mm with the typical f/4.5 Dob). Its very wide field also makes it convenient for moderate power lunar and globular cluster 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 than you do with a 60° or 70° (or even 82°) field eyepiece. In addition to Dobs, the new 25mm Explore Scientific Explore Scientific is marvelous for observing open clusters, nebulas, galaxy clusters, and globular clusters with any telescope capable of using a 2" eyepiece.

The 100° apparent field of this new 25mm 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 25mm Explore Scientific Explore Scientific has the benefits of the higher power and darker sky backgrounds that are inherent in its shorter focal length. You can use the field of view calculator in the "formula" tab above to see just how much sky the Explore Scientific can reveal with your telescope.

There is a soft rolldown eyecup to shield your eye from ambient light (from a neighbor's security light, for example) and improve the image contrast.

The 25mm 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. Here's a link to full details on this unique transferable lifetime warranty.

Tech Details

Barrel Size 2"
Eye Relief 14mm
Field of view 100
Focal Length 25mm
Number of optical elements 8
Weight 2 lbs, 10 oz
Warranty 1 year, extendable to lifetime


Review by:
This is the 100 deg ep that I'm most likely to use. Crisp images. I got an excellent buy, so I opted for the 100 deg rather than the 82 deg series. The field is so wide that in order to see the right edge, I have to move my eye to the left. Eye relief isn't as comfortable as in the 82 deg series. I ended up purchasing the 30mm 82 deg as well. Jury is still out which I like better. Be aware that it necessarily has a lot of glass so it is heavy. (Posted on 9/10/2019)
Review by:
I am using this EP with a 22 inch f/4.2 reflector. The edge correction is 'ok'. Not perfect but ok and very usable. I am not the type to stress out on stuff like that. I use it with a paracorr BTW. Build quality is excellent. One drawback, it's heavy. Make sure your able to balance it and you focuser is up to the task. I also stayed away from this EP because of other online reviews. But when I was offered a try before you buy, I figured "why not"?

Glad I did. Must have? No.... nice to have YES! (Posted on 8/23/2019)
Review by:
I own all of the ES 100 Degree eyepieces. these have stood up to abuse well, and have great eye relief. They will defiantly spoil you with the wide field of view. I will copy this review to the 14mm and the 9mm as well. these 3 are recommended if you are looking to buy a few
The 25mm, the 14mm and the 9mm are the most used (Posted on 12/14/2018)
Review by:
Reading a negative review of this eyepiece in the past kept me away from this eyepiece for years. Since the rest of my eyepieces are the ES 100*'s I decided to finally to just try the 25mm myself. It is simply awesome! I love this eyepiece! (Posted on 10/26/2018)
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