Review - TeleVue Ethos Eyepieces

The TeleVue Ethos eyepiece line has redefined the ultra-widefield observing experience [Image Credit: TeleVue].

Introduction

It took some time for me to realize that a seismic shift was about to take place in amateur astronomy when TeleVue announced a new eyepiece design at the 2007 Northeast Astronomy Forum. I had been using the Nagler Type 4 and Type 5 series for almost a decade; and like most other owners of this venerable eyepiece line, couldn't really see how TeleVue could make significant improvements to wide-field observing.

I balked at trying the Ethos 13mm when it was released due to its hefty price and the fact that I didn't need another medium-power eyepiece. But as TeleVue introduced more focal lengths to the Ethos catalog, I felt compelled to take a chance on at least one of them.

The 2010 release of the Ethos 21mm made my decision easier. Here was an eyepiece that I could directly compare to my Nagler 22mm. With the aid of the software Stellarium, I was able to see that the Ethos would offer an additional half degree to the fov at essentially the same magnification. And so, I started saving up the $795 required to buy the eyepiece (it's $894 today). In 2013, I bought the Ethos 21mm and 6mm.

Design

TeleVue has been more discrete about how they created this marvel, so I'll just directly quote from their website that "the TeleVue Ethos is essentially multiple eyepieces, delivering the true field size of a longer focal length, narrower apparent field eyepiece with the benefits of higher power and darker sky background." Obviously, trade secrets are important in a competitive environment and no mention is given as to the number of lens elements or groups used in the Ethos line.

It has been said that the Ethos line provides a "cooler" hue to stars compared to the Nagler and Panoptic lines. I would describe the stellar colors instead as being more "balanced." By that I mean stars which were more red-orange in the older eyepiece lines now appear distinctly orange in the Ethos. The same can be said of previously orange-yellow stars that now look flatly yellow, while white stars look exactly the same to me.

Eye Relief is comfortable at 15mm off the top, compared to the Nagler Type 4 or Type 5 models which have a little more per comparable focal length. The good news is that with the Ethos line, you quickly become accustomed to placing your head at the same position relative to the eyepiece.

Eyepieces

TeleVue Ethos 21mm Type 1:

Focal Length:  21mm

Apparent Field of View:  100°

Eye Relief:  15mm

Field Stop:  36.2mm

Weight:  2.25 lb [1.02 kg]

Review:

This eyepiece certainly makes a big impression on you the first time you see it. The box it came in is absolutely huge and unwrapping it for the first time brought an unscripted "ooooh!" of admiration. It's 7" tall with the eyeguards attached and just as heavy as the 31mm Nagler, but less wide and easier to hold with one hand.

Although balancing the Ethos 21mm with the Baby-Q takes some care on the Teegul Mount v2 w/ Lapides Modification, it's an absolute joy to look through. Ptolemy's Cluster - M 7 looks amazing; as if it's swimming in a sea of background stars with no edge to the field of view in sight, yet its stars are well resolved into tiny pinpoints of light. Objects that I would generally view with the 31mm Nagler for wide-field observing, like the Small Sagittarius Star Cloud - M 24, Scutum Star Cloud, and Cygnus Star Clouds, benefit from the increased magnification of the 21mm Ethos by bringing out fainter stars nestled within.

To give you an idea of the differences in observing with the Nagler and Ethos lines, let's compare the Takahashi FCT-76 with a Nagler 22mm Type 4 [a 1990's combination] to the Takahashi FSQ-85ED with a Ethos 21mm [a 2020's combination]:

The FCT-76 / Nagler 22mm combination produces 3.7° at 22x magnification;

while the FSQ-85ED / Ethos 21mm combination produces 4.6° at 21x magnification.

Or compare the Takahashi FSQ-85ED with a Nagler 22mm to the Takahashi FSQ-85ED with a Ethos 21mm:

The FSQ-85ED / Nagler 22mm combination produces 4.0° at 20x magnification;

again, the FSQ-85ED / Ethos 21mm combination produces 4.6° at 21x magnification.

That's a lot more viewable area at roughly the same magnification.

Exploring the Stellarium screenshots of the region around Lambda Sagittarii, both M 22 and M 28 can be seen in the same fov at 21x magnification with the Ethos 21mm and the Takahashi FSQ-85ED. The one key point to make about this fact is that each object lies at opposite ends of the fov; so while you can see both globular clusters in the same eyepiece at the same time, seeing them simultaneously is a bit of a challenge. That's how wide the Ethos 21mm goes! The way I approach using the Ethos line vs. the Nagler line is this: I focus on choosing the optimal magnification for the object being viewed, and then select a comparable focal length of the Nagler eyepiece I would use but from the Ethos line instead. Effectively, the Ethos will provide a similar magnification but without the limiting field stop of the Nagler [which is already very wide].

Are there any drawbacks to the 21mm? Not from a visual perspective. If your rig can handle the increased bulk and weight compared to just about any other comparable focal length eyepiece, then you should be happy. If, however, your rig is sensitive to balance issues, as might be experienced on some alt-az mounts, then the Nagler 22mm Type 4 might be the best trade-off between size, weight and performance.

All-in-all, the Ethos 21mm is as good of a wide-field eyepiece as one could hope for.

Priced ~ $895 USD.

TeleVue Ethos 17mm Type 1:

Focal Length:  17mm

Apparent Field of View:  100°

Eye Relief:  15mm

Field Stop:  29.6mm

Weight:  1.55 lb [0.70 kg]

Review:  

Priced ~ $795 USD.

TeleVue Ethos 13mm Type 1:

Focal Length:  13mm

Apparent Field of View:  82°

Eye Relief:  15mm

Field Stop:  22.3mm

Weight:  1.30 lb [0.59 kg]

Review:  

Priced ~ $658 USD.

TeleVue Ethos 10mm Type 1:

Focal Length:  10mm

Apparent Field of View:  82°

Eye Relief:  15mm

Field Stop:  17.7mm

Weight:  1.10 lb [0.50 kg]

Review:  

Priced ~ $658 USD.

TeleVue Ethos 8mm Type 1:

Focal Length:  8mm

Apparent Field of View:  82°

Eye Relief:  15mm

Field Stop:  13.9mm

Weight:  0.95 lb [0.43 kg]

Review:  

Priced ~ $618 USD.

TeleVue Ethos 6mm Type 1:

Focal Length:  6mm

Apparent Field of View:  82°

Eye Relief:  15mm

Field Stop:  10.4mm

Weight:  0.97 lb [0.44 kg]

Review:  

Priced ~ $618 USD.