Explore Scientific 9mm 100° field argon-purged waterproof 2" eyepiece


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The Explore Scientific 9mm argon-purged waterproof 2" eyepiece combines a high power capability with a 100° apparent field to provide a jaw-dropping observing experience in scopes ranging from small refractors to the largest Dobsonians and catadioptrics.
Our Product #: ES09A
Explore Scientific Product #: EPWP10009-01
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Product Description

The 9mm 100° field argon-purged Explore Scientific eyepiece is designed to provide a spectacular maximum field/medium to medium-high power image with telescopes having focal ratios as fast as f/4. It is exceptionally effective on nebulas with fast f/ratio reflectors, such as Dobsonians, giving both an immense field and a good 2mm exit pupil with the typical f/4.5 Dob that is very effective at darkening the sky background so that faint stars and diffuse objects pop out more clearly.

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 9mm Explore Scientific 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 9mm 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 9mm 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.

The new 9mm 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 several 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 9mm 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 9mm 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 9mm Explore Scientific has high contrast, comfortable eye relief, and full field sharpness - with well-controlled astigmatism, field curvature, and lateral color. The 9mm 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 the full details on this unique transferable lifetime warranty.

Tech Details

Barrel Size 2"
Eye Relief 12.5mm
Field of view 100
Focal Length 9mm
Number of optical elements 9
Weight 1 lb. 5 oz.
Warranty 1 year, extendable to lifetime


Review by:
I currently own the 9, 14, and 20mm 100-degree eyepieces. They are a joy to use, very comfortable eye relief, nice sharp image across the entire field of view, and very well made. I have compared them to the Televue Ethos line, and I cannot justify paying more for the Televue eyepieces. The ES eyepieces are that good. (Posted on 10/23/2019)
Review by:
I own the 25, 15, 9, and 5.5 100 deg. I use this 9 most on my C14, mostly for planets. Excellent quality ep. (Posted on 9/10/2019)
Review by:
I've used the 9mm ES100 with a 120mm f/7.5 APO and found it to be an extremely immersive eyepiece. This eyepiece provides a very black sky background and the field is easy to take in without blackouts. It is very sharp across most of the field. The 100 deg field just gets out of your way and lets you focus on the central field target. I've compared the 9mm ES100 with similar cost and more expensive competitors. It is hard to distinguish any of these eyepieces from each other in terms of actual performance. This eyepiece is truly an exceptional value and a great FL to introduce yourself to the 100 deg eyepiece experience. It is important to be aware that this is a 2" eyepiece even though it does not need to be. If you have a 1.25" focuser you will need an adapter to use it. (Posted on 7/25/2019)
Review by:
I have owned this eyepiece for several years and it has become my favorite for lunar viewing. Teamed up with my TMB 80mm refractor, this eyepiece offers a great full disc view of the moon with excellent contrast. It has also been a great performer when teamed with my phone’s camera for eyepiece projection photography of the moon’s features when I’d rather not use a DSLR with Powermate and back focus extensions. (Posted on 7/23/2019)
Review by:
My go to eyepiece. (Posted on 1/12/2019)
Review by:
I own the 20mm 14mm 9mm and 5.5mm ES 100deg. Wonderful field of view with enough magnification to make the background black velvet. Wonderful views. (Posted on 12/31/2018)
Review by:
I own the 20mm 14mm 9mm and 5.5mm ES 100deg. Wonderful views. (Posted on 12/31/2018)
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 25mm 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:
I love 100 degree fields of view. But I also love maximizing the bang of my astronomy dollars. The 9mm ES100 does both. (Full disclosure: I have the earlier nitrogen-purged version, purchased used.) I have looked through the competition--the costlier ones with the green paint. Both are fantastic eyepieces which give outstanding views. This is the only one I would own though, for two reasons: 1) It's cheaper, while sacrificing little, if any optical performance. 2) It's waterproof. Granted, I don't clean my eyepieces underwater. But I have gotten lens cleaning solution inside of eyepiece housings, and it is a royal pain to get that trapped moisture out. I have also seen the competitors' eyepieces fog up internally while out observing in the cold. I'm not about to pay more to take that risk. FYI, I primarily use the 9mm ES 100 in my 13" f/4.5 (167x, 0.60*) for globulars and planetary nebulae, and in my 100mm f/9 ED refractor (100x, 1.00*) for open clusters. This is another lifetime keeper from ES (I also have the 14mm ES100.) (Posted on 11/6/2018)
Review by:
I would have to put Explore Scientific eyepieces right up there with Baader Planetarium. They might not be quite as good as BPs, but it's difficult for me to tell the difference, especially when you factor in the cost. Dollar for dollar, I don't think you can do much better.
I use these EPs on my LX90-12 ACF and they perform exceptionally well. The view is crisp right to the edge and I love the way stars pop into pinpoint focus when I hit the focal point. No reflections or astigmatism that I can tell. I especially like having them filled with an inert gas (all of mine are argon filled) and have never experienced any fogging inside of the lenses. These eyepieces with the wider field of view is truly like looking through a porthole out into space and the longer eye relief and larger exit pupil make it much easier on my tired old eyes. (Posted on 10/7/2018)
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