3.7mm 1.25"/2" 110° field Ethos-SX

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Nearly half a century ago, Al Nagler designed the optics for the LEM (Lunar Excursion Module) simulator that was used to train NASA astronauts how to land on the Moon during the Apollo program. From Apollo 11 through Apollo 17, every astronaut pilot who landed on the Moon trained using Al’s optics to learn how to do it.

Years after the LEM program ended, the memory of the 110° view of the simulated moving lunar surface seen through the triangular cabin window of the LEM simulator inspired Al to develop an “Ultra Wide Angle” telescope eyepiece to approach that lunar landing “simulator experience.” That eyepiece was the famed 82° field Nagler. When the first Nagler hit the observing fields, it changed forever how amateur astronomers viewed the heavens. An early customer dubbed it a “spacewalk” view.

But the 82° Naglers, and even the recent 100° field Ethos eyepieces, didn’t duplicate the original 110° LEM simulator experience Al remembered. So Al pushed Ethos designer Paul Dellechiaie to extend the field of the Ethos design to reach a full 110°, the same astonishing field as the LEM simulator. The result is the 3.7mm Ethos-SX (Simulator eXperience) eyepiece – a Sky & Telescope Hot Product for 2011.

Essentially, “the experience” is about creating an image as natural as one sees with the unaided eye. With Paul's help, Al's initial dream for amateur astronomers is now fully realized. The 3.7mm Ethos-SX is designed and crafted to combine its exceedingly wide field of view with all the contrast, color-rendition, distortion correction, and center-to-edge sharpness needed to achieve that natural view.

Beyond the desire to simply achieve 110°, the extended field of view gave TeleVue the ability to produce a superb planetary eyepiece with a deep sky true field of view that logically fits within the rest of the Ethos eyepiece line. With a 110° field, the Ethos-SX has 21% more apparent field of view area than the 100° Ethos design. This permits a nice 62% power increase from a 6mm Ethos, while still retaining 68% of its true field of view. The 3.7mm actually has more true field of view than a TeleVue 8mm Plössl, 6mm Radian, or 5mm Nagler Type 6!

The 3.7mm is a 1.25" format eyepiece and is parfocal with a wide range of 1.25" TeleVue Plössls, Panoptics, Radians, Naglers, Nagler Zooms, and 6mm and 8mm Ethos eyepieces. It can be used with the TeleVue DIOPTRX eyesight astigmatism corrector. The included screw-on 2" adapter lets you use the 3.7mm Ethos-SX in a 2” star diagonal or focuser and is designed to make the eyepiece parfocal with the 13mm and 10mm Ethos eyepieces when they are used in their 2" modes.

We don't think we can aptly describe Al’s original experience of “flying over the moon” in the LEM simulator, but for the first time, YOU can experience what the astronauts saw four decades ago. For example, with a TV-85 refractor (or any similar 600mm focal length scope), the actual field of view is 0.67°, so that the entire full Moon fits into the eyepiece field – but at a magnification of 162x! Talk about getting up close and personal with the lunar surface!

Field of view:
The field of view (FOV) is the amount of observable world one can see at any given moment.
110°
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.

15mm
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.

3.7mm
Barrel Size:
The industry standard diameter, as of 2011, is 1.25" and is the most common.  Other sizes available are .965" and 2".
1.25"/2"
Weight:
The weight of this product.
17.7 oz.
Warranty:
Limited Lifetime
Reviews from Cloudy Nights (www.cloudynights.com)
These reviews have been written by astronomers just like you and posted on the Cloudy Nights astronomy forums . . .
Ethos SX 3.7mm: An Extensive Review

User Ratings/Reviews from our Customers (www.astronomics.com)
Overall Product Rating: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics(0.00)   # of Ratings: 0   (Only registered customers can rate)

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Telescope Eyepiece Formula
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TeleVue - 3.7mm 1.25"/2" 110° field Ethos-SX

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TeleVue - 3.7mm 1.25"/2" 110° field Ethos-SXLifesize image of the TeleVue 3.7mm Ethos in its 2" adapter.Lifesize image of the underside of the 2" adapter of the TeleVue 3.7mm Ethos.
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Our Product #: TE03
Manufacturer Product #: ETH-03.7
Price: $650.00
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The TeleVue 3.7mm Ethos-SX eyepiece shows you the same 110° view of space and the Moon that the Apollo astronauts saw when they trained to land on the Moon. The TeleVue 3.7mm Ethos is a Sky & Telescope Hot Product for 2011 . . .





. . . our 34th year