TeleVue Ethos 4.7mm 110° FOV vs Explore Scientific 5.5mm 100° FOV

By: Vlad Fedosov

Intro:

This is not my first encounter with TeleVue Ethos line of eyepieces. In the past, I have owned and reviewer the 3.7mm Ethos(see review) and 13mm Ethos(see review). From these past experiences, I knew first hand that these are an exceptional eyepiece but was still curious to see how the 4.7mm Ethos would stack up to my personal workhorse eyepiece in this focal length the Explore Scientific(ES) 5.5mm 100°! The 4.7mm Ethos MSRP’s for $628, has an eye relief of 15mm, and weighs 20.8oz. The ES 5.5mm retails for $449.99, has 10.5mm of eye relief, and weighs 21.6oz. So can the ES 5.5mm give the Ethos 4.7mm a run for its money? Let’s find out!

Testing:

I evaluated these eyepieces from my semi-dark sky(green zone) 5.5mag back yard in the Portland, OR area. The scope used for the test was a TeleVue TV-85 APO. Conditions on the nights of evaluation had about average seeing and transparency(one night was somewhat hazy). Since I was doing this comparison in the winter months we had a wealth of perfect objects to evaluate these very wide field of view eyepiece. What are they? Open star clusters of course! Open star clusters generally will fill the field of view(FOV) of these eyepieces to the point that it is relatively easy to evaluate the overall edge correction of the eyepiece.

Before we get to the correction of these guys I decided to just take a look at a few double stars with the eyepieces and get a sense of how sharp they are. Well try as I might I could not see any difference in the view that they provided. I then moved onto the now small disk of Mars which was still high in the sky in the evening. After switching from one eyepiece to the other I could not decide on a clear winner so I concluded that they are both very sharp performers on axis! Contrast seemed about even also with a possible slight edge to the TeleVue.

Next, I moved on to taking a look at m45 and the Double Cluster. This is where the difference in the eyepieces became fairly obvious. The very first thing that I noted is how mind-bogglingly sharp the Ethos is in rendering stars all the way to the edge! It was just incredible to have my head sideways looking to see the edge of the FOV of the eyepiece and see stars as perfect little orbs! The ES 5.5mm is not bad in this regard but is certainly not as well corrected. It will start to show coma(stars start to look like little comets) at about 80% of the FOV. This is not something that is a huge bother in normal use but when you compare the eyepieces side-by-side it’s an obvious difference in performance.
Moving onto the overall experience of using the eyepieces. I always find it amusing how they derive the eye relief on these hyper-wide eyepieces??? The Ethos 4.7mm is listed as having an eye relief of 15mm. Yes, you can have your eye at 15mm away. How much of the FOV can you actually see at that distance? Maybe 50°! In reality, maybe I’m just a “weird” observer but I like to take in the entire FOV to the field stop all at once! With any of these hyper wide eyepieces that I have tried you really need to have your eyeball maybe 2mm off the glass to see the field stop. The 4.7mm takes this a step further and I don’t think I can see the entire field stop at all no matter how close I get…! At first, this really bothered me, but the more I used the eyepiece the more I came to embrace the totally immersive feel of just looking around the FOV of the eyepiece by moving my head around to see different parts of it. It’s really kind of looking out the window of a starship! Overall I would put the FOV that you can actually see all at once is around 100-105°. 110° is just not possible with my eyeball

Now how is the FOV comparable in the 5.5mm ES? Well like I said my eye needs to be nearly touching the glass but I can see the entire field stop. This is how I normally observe with these eyepieces and what I’m used to. Perhaps I’m an outlier in this respect because I cannot count the number of times that I have taken a look through people’s scopes at star parties that have an Ethos in the focuser and their eye guard is up on the eyepiece. I mean at most you can see like 60° of the FOV without moving your head around to see the other parts of it. The way I see it, you might as well buy 60° FOV eyepieces… Again that’s just me.

Conclusion:

So is the Ethos 4.7mm better than its ES rival? In the absolute sense of raw performance; YES! This is primarily true in regards to the performance of the edge correction. If you are using a fester scope(~f/6 or faster) and your actually going to look at the edges of the FOV(which is not that easy) then the Ethos has a clear edge(lol). If you have a slower scope or one of the many folks that I meet using these with the eyecup up you may not notice the wider FOV or edge performance of the eyepiece. I would honestly be quite pleased with either eyepiece in my eyepiece case!