Explore Scientific 100° 25mm, 14mm, and 5.5mm Eyepiece Review

By: Vlad Fedosov
03/27/2019

Intro:

When I got started in amateur astronomy in the late ’90s the TeleVue Nagler line of eyepieces was the thing of dreams. It was the absolute top of the line eyepieces with a massive 82° field of view(FOV). Fast forward a few years and Al Nagler did it again by introducing the 13mm Ethos eyepieces with a seemingly unreal 100° FOV that is corrected right to the edge of the FOV. On its heals Explore Scientific(ES) soon introduced their own line of 100° FOV eyepieces. Once these became commonly available I could not resist the urge to try out what this new breed of eyepieces was all about and picked up the 14mm ES 100° FOV eyepiece to see how it would stack up to the set of 82° ES eyepieces that I owned. Well, I guess I have to give the results away in the intro and title as I ended up owning the 25mm, 14mm, and 5.5mm ES 100° FOV eyepieces.

Testing:

Once I received the ES 14mm 100° FOV eyepiece I immediately started comparing it to the ES 14mm 82° eyepiece. A bit of back story: over the past years I convinced myself that the 82° FOV is worth the upgrade over 68° even though I find that 68° is the sweet spot in regards to a wide FOV and comfort of taking it all in at once(even though I have the 100° eyepieces I regularly use my ES 40mm and 24mm 68° eyepieces because they are sooo comfortable to use!). Could the 100° be as comfortable as the 68° or at least the 82°? Well, in short, I quickly found out that this is not the case… You really need to be right by the glass to see the entire FOV at once. This is, even more, the case then with the 82° FOV eyepiece. At one point I was really close to sticking to the 82° eyepieces until I reasoned that I can use the 100° eyepiece with less critical eye placement compared to the 82° eyepiece and still see the same 82° field. This sold me on the upgrade to the 100° FOV eyepieces. It is also nice to see the crazy wide field of an object when I really want to by getting really close to the glass. In my initial testing of the two 14mm eyepieces, I did not see a significant difference in contrast and sharpness when comparing the 82° and 100° ES eyepieces.

After being satisfied by the nice performance of the ES 14mm 100° the next eyepiece that I purchased is the 5.5mm 100°. This eyepiece was more of the same goodness! I did not notice any downsides of the eyepiece compared to the 14mm. It is especially nice to have the 100° FOV at the high power range in a manual dob as you have a longer time between re-centering the object being viewed. The weight of the 5.5mm 100° is certainly more compared to the equivalent 82° eyepiece so if this is a consideration for you keep this in mind.

Last up was considering replacing my ES 30mm 82° FOV with the 25mm 100°. This eyepiece got a bad rap from 1 bad review early on it its life. This kept me from getting one for a while until I finally just decided to see how it performs for myself. Its an awesome piece of glass! Is the Ethos 21mm sharper at the edges? Sure! But its a 21mm, not 25mm. You get a much wider FOV with the 25mm and let's be honest no one observes objects at the edge of the FOV of a 100° eyepiece. Depending on what scope you are using the outer 10-20% or so of the FOV is not 100% sharp. Stars to coma out a bit. I do like that the eye placement is not super crucial with the eyepiece. Just like any 100° eyepiece you do need to be right by the glass to see the entire FOV at once. Overall the views are amazing though with the 25mm! It works equally well in my Dob and my APO's and especially SCT's(due to the slower f/). When I'm at a star party and have my 18" dob out the 25mm rarely leaves the focuser. Sharpness and contrast are on par with other eyepieces such as the ES 68/82° and TeleVue. I have used the eyepiece during the day and I do find that the blackout with it is quite bothersome(it's really like a dark orange color). Based on what I have seen I would not recommend it for daytime use.

Conclusion:

In conclusion, I’d like to say that the ES 100° FOV eyepieces are the best value in a general use hyper-wide field eyepiece around. Are the Ethos eyepieces better? Yes they are. I have compared my ES’s to the Ethos at star parties on many occasions. I would rate the difference in performance in regards to on-axis sharpness and contrast to within 1-5% of each other. The edge performance of the Ethos is in the range of 10% better. I think you are the only person that can answer the question of whether paying twice as much for an eyepiece is worth it to get 5-10% better performance. In all honesty, the main reason that I do not own all TeleVue eyepieces is that they do not have a 25mm 100° FOV eyepiece. The other thing that keeps me from buying TeleVue these days(I used to own all TeleVue) is that at the very premium price that they charge for their eyepiece they should all be MADE IN THE USA! There are zero excuses for them not to be made in the USA besides a higher margin for TeleVue. For the money, you really can't go wrong with the ES 100° FOV eyepeices.