Tele Vue 3.7mm Ethos-SX Eyepiece

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Tele Vue 3.7mm Ethos-SX Eyepiece

The 3.7 mm Ethos-SX Eyepiece (the Simulator eXperience) is part of the Tele Vue Ethos Eyepiece Series.

Al Nagler eagerly pushed Ethos designer Paul Dellechiaie to extend the new 3.7 mm focal length to reach 110 degrees, the same field as the LEM Simulator optics Al designed over 50-years ago (in the 1960s) to train NASA astronauts for lunar landings.  Years after the LEM program, the memory of the 110 degree view of the simulated lunar surface moving through the triangular cabin window of the LEM inspired Al to develop an 'Ultra Wide Angle' (his patent title) telescope eyepiece to approach that 110 degree 'simulator experience.' When the 82 degree Nagler eyepiece hit the observing fields, it changed how amateur astronomers viewed the heavens. An early customer dubbed it a 'spacewalk' view. 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 Tele Vue 3.7mm Ethos-SX eyepiece 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 degrees, the extended field of view gave Tele Vue 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 110 degrees, the Ethos-SX has 21 percent more AFOV area than the 100 degree Ethos design. This permits a nice 62 percent power increase from a 6 mm Ethos, while retaining 68 percent of its TFOV. The 3.7 mm actually has more TFOV than our 8 mm Plossl, 6 mm Radian, and 5 mm Nagler Type-6!

The 3.7mm is a 1.25-inch format and is parfocal with the wide range of 1.25-inch Tele Vue Plossls, Panoptics, Radians, Naglers, Nagler Zooms, and 6 mm and 8 mm Ethos eyepieces. The screw-on 2-inch adapter (included) is designed to make it parfocal with 13 mm and 10 mm Ethos when they are used in their 2-inch modes.

Tele Vue 3.7 mm Ethos-SX Specifications...
  • Model: 3.7 mm Ethos-SX 110 (Simulator eXperience)
  • Apparent field: 110 degrees
  • Focal length: 3.7 mm
  • Effective field stop diameter: 7.04 mm
  • Eye relief: 15 mm (accepts DIOPTRX eyesight astigmatism corrector)
  • Weight: 1.10 lb/ 17.7 oz; 2-inch adapter/stand: 2 oz
  • Size Barrel: 1.25-inch
  • Includes 2-inch adapter


OPT Product Number: TE-ETH-03.7



Dust Caps IncludedYes
ER15mm to 19mm
Eye Guard IncludedYes
Eye Relief15mm
Eyepiece OpticsEthos
Field of View110 degrees
Field Stop7.04mm
Focal Length3.7mm
FoV100 Degrees or More
Free ShippingYes
ManufacturerTele Vue
ModelTelevue Ethos
WarrantyLifetime Warranty