20mm 100° field waterproof 2" eyepiece

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The 20mm Explore Scientific 100° field 2” eyepiece is O-ring sealed and nitrogen-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 nitrogen 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 20mm Explore Scientific eyepiece, has high contrast, comfortable eye relief, and full field sharpness – with well-controlled astigmatism, field curvature, and lateral color. Its nine element 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 (almost 4.5mm 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 20mm 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 20mm 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 20mm 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. With an eye relief of 14.5mm, the 20mm 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 20mm 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 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.
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.

14.5 mm
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.

20mm
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.
2 lbs. 2 oz.
Warranty:
1 year, extendable to lifetime
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1. Jim on 5/17/2013, said: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics
I can't bring myself to pay for the other 100 degree EP on the market, but the ES 20 mm at the 300 dollar price point made me bite. Good gravy, is that view wide. And clear and sharp. The EP is also extraordinarily large and heavy and well made. I eventually purchased all four in the line up. They work well in all my scopes and I'm pleased with the purchase(s).
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2. Herbert R on 4/30/2013, said: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics
The views through this 20mm is simply outstanding. This EP is perfect for open clusters, double clusters, galaxies and big nebula. I'm a wide FOV nut so the 100* series is my favorite. The image is crystal clear and tack sharp all the way to the edge of the FOV. The images have great contrast with pinpoint stars in the whole FOV. I have the ES 100* 9mm and the ES 82* 30mm and they too are spectacular EP's but I always find myself going back to the 20mm. The 20mm also barlows exceptionally well too. Its a perfect addition to my fast 10" Dobsonian.
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85mm x 120mm eyepiece container
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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 - 20mm 100° field waterproof 2" eyepiece

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Explore Scientific - 20mm 100° field waterproof 2" eyepiece
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Our Product #: ES20
Manufacturer Product #: EP10020-00
Price: $299.99  FREE ground shipping - Click for more info
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The 100° apparent field of the Explore Scientific 20mm waterproof 2" eyepiece provides superb maximum field/medium power observing in all scopes, from small apo refractors to the largest Dobsonians and catadioptrics . . .





. . . our 34th year