Brands - JMI



TeleVue 3.7mm Ethos SX Eyepiece


SKU: ETH-03.7
Manufacturer: TeleVue
Availability: IN STOCK
Eyepiece Focal Length: 3.7 mm
Apparent Field: 110 degrees
Eye Relief: 15 mm
Barrel Diameter: 1.25 and 2 inches
Eyepiece Weight: 17.6 ounces


This is the shortest focal length in the Ethos lineup and is primarily useful in short focal length refractors and fast Newtonian systems. The expansive 110 degree apparent field allows you to use more magnification while still fitting your target object within the field. 

The TeleVue 3.7mm Ethos SX eyepiece raises the bar in ultra wide field eyepieces yet again. The new 3.7mm Ethos SX is the world's first astronomical eyepiece to feature a 110 degree apparent field. News of this eyepiece reminded us of a star party presentation by TeleVue founder Al Nagler entitled "Eyepieces that Swallow Spaceships." In that presentation Al described his contribution to the Apollo lunar missions, which was to develop the simulator optics for the Lunar Excursion Module (LEM.) The astronaut's field of view through the windows of the LEM was - you guessed it - 110 degrees!

We find that comparing eyepieces of different designs can help put the concept of a 110 degree apparent field into perspective. Consider the 3.7mm Ethos SX alongside a 5mm Nagler (82 degree AFOV) or an 8mm Plossl (50 degree AFOV.) All three eyepieces offer up approximately the same true field of view, meaning that patch of sky you see through the eyepiece would be the same. The magnification and image scale offered by the Ethos SX would be 35% greater than that of the 5mm Nagler, and more than double that of the 8mm Plossl. The advantages of all this field of view are twofold. First, a wider true field offers more observing time before adjusting the telescope position. This is important to anyone with a mount that does not track the target. Second, it allows you to observe the same object at higher magnification. This latter point is important regardless of whether the telecope mount tracks the target.

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