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

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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.

Field of view:
The field of view (FOV) is the amount of observable world one can see at any given moment.
100°
Eye Relief:
Eye relief is the distance from the last surface of the eye lens of an eyepiece to the plane behind the eyepiece where all the light rays of the exit pupil come to a focus and the circular image is formed, sometimes called the “Ramsden Disk.” This is where your eye should be positioned to see the full field of view of the eyepiece. If you must wear glasses because of astigmatism, you’ll usually need at least 15mm of eye relief or longer if you want to see the full field of view with your glasses on.

A note on our eye relief figures: Quite often, our eye relief figures will differ from those of the manufacturer. This is because we measure the “usable” eye relief, while the manufacturers specify their usually-longer (but technically correct) “designed” eye relief.

The eye lens of the eyepiece is normally recessed below the rubber eyeguard or rubber rim of the eyepiece to keep the lens from being scratched during use. An eyepiece might have a “designed” eye relief of 15mm (and the eye relief will truly measure 15mm from the eye lens to where the image forms). However, if the eye lens is recessed 3mm below the eye guard, the Ramsden Disk forms only 12mm above the eyepiece body (the 15mm “designed” eye relief, less the 3mm of eye relief made unusable by having the eye lens recessed into the body of the eyepiece). This “usable” eye relief of 12mm (measured from the rolled-down eyeguard – the closest point you can get your eye to the eye lens – to where the image forms) is the eye relief figure we would measure and list in this website.

Why is it important to list the “usable” eye relief? For those people who don’t wear eyeglasses while observing, a few mm difference between the eye relief they expect from the manufacturer’s literature and the shorter eye relief they actually get in real life doesn’t mean a lot. They can simply move a little closer to the eyepiece to see the full field, and never realize that the eye relief is a little shorter than they expected. However, some people must wear eyeglasses while observing, because of severe astigmatism. These observers can’t move closer to the eyepiece if the eye relief is shorter than expected because their glasses get in the way. For these people, the real life “usable” eye relief is more important than the technically correct but sometimes not fully usable “designed” eye relief. We measure and list the actual usable eye relief so that people in the real world can pick the eyepieces that will work best for them.

12.5mm
Focal Length:
This is the length of the effective optical path of a telescopeor eyepiece (the distance from the main mirror or lens where the lightis gathered to the point where the prime focus image is formed). Focallength is typically expressed in millimeters.

The longer the focallength, the higher the magnification and the narrower the field of viewwith any given eyepiece. The shorter the focal length, the lower themagnification and the wider the field of view with the same eyepiece.

9mm
Number of optical elements:
9
Barrel Size:
The industry standard diameter, as of 2011, is 1.25" and is the most common.  Other sizes available are .965" and 2".
2"
Weight:
The weight of this product.
1 lb. 5 oz.
Warranty:
1 year, extendable to lifetime
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Helpful Formulas
Telescope Eyepiece Formula
To calculate the magnification and approximate actual field of view of this eyepiece on your telescope, enter the focal length of your telescope below and press the "Calculate" button.

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

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9mm 100° field argon-purged waterproof 2" eyepiece
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Our Product #: ES09A
Manufacturer Product #: EPWP10009-01
Price: $339.99  FREE ground shipping - Click for more info
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MSRP: $756.99
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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 34th year