By: Vlad Fedosov
A 3.7mm 110° FOV eyepiece? An interesting idea indeed. My usual eyepiece in this focal range is a 5.5mm 100° Explore Scientific unit. I have always been curious to try a TeleVue equivalent and finally got the chance!
I tested the eyepiece on a moonless night in my mag 4 light polluted backyard. Seeing and transparency were about average for where I live in the Northwest. The telescope used was a William Optics GT102 triplet APO.
I used Algieba as an evaluation star for the eyepiece. The 3.7mm Ethos produced 190x with the 102mm APO making the split of Algieba very easy. After simply enjoying the view of this showcase double for a while I noted that I was very impressed with how wide the FOV was. Even though I’m used to 100° FOV eyepieces this one seemed a lot wider than the extra 10° would make you believe. This might be somewhat of an elusion as the eye relief is absolutely nonexistent if you want to attempt to take in the entire FOV all at once. Having said that I found this eyepiece very easy to use and enjoy as long as you are ok only using about 80% of the entire FOV and then just moving your head around to see the rest when needed(although to me that somewhat defeats the purpose of having a massive 110° FOV…).
I did not initially note any distortion in the surrounding stars around Algieba but decided to do further testing to see if I was right. To evaluate the performance further I moved Algieba progressively towards the edge of the FOV to see where the distortion would start. I like using an APO for this as the airy disk is very well defined and will start to show distortions much easier the actual star will. I was quite impressed as Algieba was split all the way to the edge of the FOV. The airy disk did start to exhibit distortions at about 70% of the FOV progressively getting worse as you went towards the edge. I think the performance excellent for such a massive FOV. Nice job TeleVue!
Would I recommend the 3.7mm Ethos? Absolutely, if you do not wear glasses! Also do keep in mind that if you are like me and like to take in the entire FOV to see the context of the object being observed, you will have a very tough time doing so. I do find the 5.5mm Explore Scientific eyepiece a bit easier to use in this regard but it does have 10° smaller FOV so that is no surprise.
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