9mm 120° field argon-purged waterproof 2" eyepiece

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The new 9mm Explore Scientific has a hyperwide apparent field of view that’s an immense 120° across! It’s the widest field of view available in any commercial eyepiece. An astronomy first from Explore Scientific, the 120° apparent field of this new 9mm Explore Scientific shows more than twice the sky area of an 82° eyepiece and even a whopping 44% larger area than a 100° eyepiece.

The prototype 9mm was field-tested for the first time at Starfest in Canada, August 2011. Experienced astronomers who waited in line to get a chance to view through the hyperwide 120° Explore Scientific 9mm were stunned by the full-immersion observing experience. Even when compared with a 9mm 100° field eyepiece, the difference was “quite palpable,” to quote one experienced observer. The telescope seemed to truly disappear in the 120° field, bringing them face to face with the Universe in an intimate and personal way never before possible. It’s an awe-inspiring observing experience you can repeat for yourself every night you go out with your scope.

This deep sky eyepiece, the first of its kind for astronomy, produces a highly corrected field across its entire 120° apparent field. The views of compact globular clusters, nebulas, and galaxies are breathtaking. You can use the field of view calculator under the formula tab above to see just how much sky the Explore Scientific can reveal with your telescope.

The Explore Scientific 9mm is designed specifically for nighttime deep sky observing. It is not an eyepiece for daytime use and will show some lateral color at the edges of the very wide field in daytime use. This lateral color is not visible during the nighttime observing at which this unique eyepiece is designed to excel.

This 2” Explore Scientific 120° eyepiece is O-ring sealed and argon-purged to be 100% waterproof. Internally sealing the eyepiece and purging it with inert, dry argon gas (which has lower permeability through the eyepiece's polymer seals than nitrogen) 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 9mm Explore Scientific eyepiece, has high contrast and full field sharpness – with well-controlled astigmatism, field curvature, and lateral color. Its twelve element/eight group optical system (using lenses of dense crown, light crown, dense flint, and lanthanum rare earth optical glasses with 15-layer multicoatings on all air/glass surfaces) is designed for maximum field/high power deep space use with telescopes having focal ratios down to f/4 and below.

Its very wide field makes this 9mm eyepiece convenient for observing with Dobsonians, as you have much longer to observe before an object drifts out of the field and the scope has to be repositioned than you do with a 70° or 82° (or even 100°) field eyepiece.You can use the calculator in the "formula" tab above to see just how wide a field of view this unique eyepiece will show you with your particular 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 eye relief is a comfortable 13mm.

The 9mm Explore Scientific fits 2" focusers only. A shallow tapered groove is machined into the 2" chrome barrel to engage your focuser thumbscrew or compression ring. This helps prevent the eyepiece from falling should the thumbscrew accidentally loosen while observing. The sides of the groove are slanted to avoid catching on your focuser's compression ring when removing the eyepiece from your scope.

This individually serial numbered Explore Scientific eyepiece is backedby a limited one year warranty, which will be extended to an ExploreScientific transferable product lifetime limited warranty when its warranty card is registered with Explore Scientific within 60 days of purchase.With the extended product lifetime warranty, this Explore Scientificeyepiece will be protected for as long as it continues to bemanufactured, plus an additional five years. 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.
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.

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.

Number of optical elements:
Barrel Size:
The industry standard diameter, as of 2011, is 1.25" and is the most common.  Other sizes available are .965" and 2".
The weight of this product.
3 lbs.
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.

Enter your telescope's focal length: mm   

Explore Scientific - 9mm 120° field waterproof 2" eyepiece

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Explore Scientific - 9mm 120° field waterproof 2" eyepiece
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Our Product #: ES12009
Manufacturer Product #: EPWP12009-01
Price: $799.99
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Clear skies,

A first from Explore Scientific, this 2" 9mm deep sky eyepiece has an immense 120° field that seems to make your telescope disappear and plunge you headfirst into the Universe . . .

. . . our 38th year