I have played with these eyepiece, I have owned these eyepiece and now I finally am comfortable with the two that I settled on. Let me state up front I am not going to review the 14mm ES 100 degree eyepiece because for my situation, I opted out of getting that eyepiece. The 14mm provides a clear, crisp image, a wide field of view that allows for an object to drift through the field of view allowing the observer to study it if that is their choice. However, for me, the 9mm does that equally as well and I much prefer the magnification of the 9mm over the 14mm.
Now, let me state up front that I own the 9mm and the 20mm ES 100 degree eyepieces and these are the two I am keeping. No Ethos? Nope, I have alluded to this in other posts, I can afford the Ethos, I can afford the 6mm, the 10mm, the 13mm, the 17mm and the 21mm IF I opted to. I don't opt to. A long time ago in this hobby I made the commitment and made a personal objective that I would not spend any more money on this hobby than I could afford or to get a product that I found very useful. It also meant making choices on my equipment that have made sense for me in a variety of ways while keeping me focused on what I spend. In life, hobbies, jobs, relationships, material things etc. will eat up as much time or money as you want to sink into them. To be successful in life one has to know when to put in a ton of time, when to back off, what limits to set for oneself and how much money one is willing to spend. I openly admit, in my life I have been blessed with the opportunity to make income for several ways. That has met I have sufficient for the needs of my wife and I, to help others out and to enjoy some things in life. What does this have to do with an eyepiece review? A lot. If you understand that about me, you will understand why I drive a Subaru Outback and not a more fancy crossover. Though not perfect, the Outback is very, VERY useful and provides me with what I need. That is the same for the Explore Scientific 100 degree line versus the Ethos. The Ethos are the elite but the Explore Scientific 100 degree eyepieces are very close and thus are very, VERY useful.
For me the Ethos are the top line in uber wide field viewing right now. I believe they have been for some time. However, when I compare the 9mm ES 100 degree to the 10mm Ethos, the 9mm ES is close enough that for me that the ES 9mm 100 degree though not perfect, and perhaps 90% of the Ethos 10mm, that means that for the price difference, the ES 9mm 100 degree becomes an extremely useful eyepiece when my goal is a wide field experience.
The 9mm Explore Scientific 100 degree eyepiece is a well crafted eyepiece. For the remainder of this review I will call it the 9mm ES. The 9mm ES have some positives that I like about it. First, I love the fact that you can place an object on the outer edge and just watch, watch, watch, and watch that object some more as it floats across the field of view. The views are sharp, crisp edge to edge and enjoyable. You definitely get an immersive or space walk feeling using them. Last for me, the 9mm and the 20mm (throw the 14mm in there also if you want) ES provide a viewing experience that can end the need for multiple type of eyepieces at different focal lengths.
The 9mm ES though has some cons and those are significant for me. The first is not a deal breaker, I have left my dobs with sufficient counter weight to offset any heavy eyepiece and the ES 9mm is a heavy eyepiece. It it the lightest of the three, but still rather heavy. The 9mm ES is listed in at 1lb 8oz so yes, combine that with a Paracorr Type II and you will be tip heavy if your scope does not have sufficient counter weights. Not a deal breaker though for me.
There is coma in the eyepiece, and that to me is evident when I use them in one of my dobs. Though not glaring, it is enough that to me it can by annoying but in a wide field like this, I spend most of my time in the center of the FOV, and thus coma on the outer edge is not a big deal. As stated, I can put them into a Paracorr Type II and that cleans it up.
The next are the 9mm ES tend to fog up easily because of their short eye relief. This means you will need to keep a dew heater strip on them while observing if dew is an issue. It isn't for me, so again, not a deal breakers.
However, this last con is a deal breaker for me. The 9mm ES is listed with 12.5mm eye relief, and I personally think it is a little bit less, not much, just a tad. This means no eye glasses or you will need to successfully compensate for the use of glasses if you wear them. A dipotrix could help with astigmatism but for me, someone who can prefer to wear my eyeglasses at times observing, the short eye relief gets in the way.
On my telescopes with my ES AR102, the 9mm ES works wonderfully. It is perhaps one reason I keep it. In my 10", 14", 17.5" and 24" dobs, the eyepieces work, but they require some extra effort for me to feel comfortable using them. The go from being very useful in my book on my dobs to somewhat useful.
I do want to touch on why not the 14mm over the 9mm ES 100 degrees? I use to LOVE the 14mm or 13mm view/magnification through an eyepiece. Then about 8 years ago as I progress in my own observing style, I found out that for me, the 10mm is my starting area for viewing details on MOST (not all, but most) DSO's. There is enough magnification difference (in my 17.5 the 14mm would provide 143x and the 9mm 222x while in my 14" it comes to be 14mm 117x and the 9mm is 182x) that when I am studying, observing and sketching an object, that extra 60x or so is enough to shot some detail that I wouldn't see. Granted, sky conditions have to allow use of the 9mm or a 10mm, but where I live, they usually do year round. So for me, the key magnification is the 9mm over the 14mm. Your mileage may vary (YMMV) from my experience and tastes, and there is nothing wrong with that.
To rate this 9mm ES I would give it the following:
Eye Relief: 3/5 (4/5 IF you don't wear glasses)
An excellent eyepiece that is used by the right observer will bring hours of useful joy in gazing upwards.
The ES 20mm 100 degree eyepiece or ES 20mm as I will call it is a well built, excellent performer. Again we see here an eyepiece that is useful to the owner, VERY useful and at a price that will leave additional income in your wallet to save, spend on other items or to simply enjoy. Here when I compare it to the 21mm Ethos I see about 88%-90% of the performance of the 21mm Ethos. That is very close in my book and close enough that for me I have purchased and kept the 20mm ES. Color is good here, stars are sharp across the field of view and its a pleasure to observe with. Very similar field of view to one of my favorite wide field eyepieces, the TeleVue 26mm Nagler.
The cons are similar to the 9mm ES above. Weight is one issue. Here the 20mm ES weighs in at 2lbs 2oz, and yes, that is a LOT of weight. You will need to balance your scope after putting in this eyepiece if you haven't in the past. Coma is similar to the 9mm, perhaps a little bit more yet a coma corrector clears it up for me on my dobs. More importantly, with the 20mm ES I do see some off-axis astigmatism. Not bad, but it is there if one knows what one is looking for. Weight though can easily be modified so there is no impact to the scope and to the balance of the scope. Dew on the lens is an issue again and that slightly longer eye relief at 14.5mm or something perhaps just slightly less, is more than the 9mm ES, but not enough if your an eyeglass wearer. You can remove your eyeglasses if you wish but as mentioned, you will need a way to compensate for the astigmatism if you suffer from that.
In my scope, the 20mm ES works wonders when I just want to scan or need a wide field finder eyepiece. That is how I use it. My uber wide field is the 30mm ES 82 degree eyepiece. This is another great eyepiece offered up by Explore Scientific. There is an argument that since I use premium optics in my telescopes, why wouldn't I use premium or the best of the best eyepieces? Because I do, they are the Pentax XW and TeleVue Delos eyepieces are for me, the premium eyepieces I use and some orthos.
The Explore Scientific 9mm and 20mm 100 degree eyepieces are extremely good eyepieces, and they allow me to scan quickly, and to let some optics drift at 9mm. I do not use them on a regular basis because of their eye relief, except on my Explore Scientific AR102 refractor (still use my Pentax XW and Delos more though). Because of their eye relief they will not be everyday eyepieces for me, and neither would the Ethos. As a result I opt to have a very useful eyepiece, the 9mm and 20mm ES 100 degree eyepieces that save me the cost, give me very good view and I can use to sweep, drift or as an outreach eyepiece at a star party or to loan at a private observing session. I am glad I have them, not going to part with them, and they have a place in my eyepiece collection.
Eye Relief: 3/5 (4/5 IF you don't wear glasses)
My ratings for each eyepiece is the same, and though not perfect, they are as I have said, EXTREMELY useful if you don't want to pay for the cost of a TeleVue Ethos. My main eyepieces are the Pentax XW and the Delos, because I believe they give me a sharper and crisper view of a wider variety of objects and I love that 70 degree to 72 degree field of view. Visually, that is where I am at and I really am comfortable with it. So if your by my scope one night, you'll find a Pentax XW or a TeleVue Delos in the focuser more often that not. You may find depending if I am sweeping or wanting a LONG magnified look at an object the 9mm ES 100 or 20mm ES 100 degree eyepiece in the focuser. They are also the two eyepieces I will loan out if someone is observing with me and don't have a set of good eyepieces. I trust them enough to share them. If you are considering them, and understand the pros and cons I have shared and can live with them, AND you have the cash, go ahead and purchase them if you want. They work well for me and I would hope they would work well for you!
Next up for an eyepiece review, a shoot out between the ES 20mm 100 degrees and one of my favorite eyepieces, the 30mm 82 degree Explore Scientific. I know which one I prefer already and which gets more use. Why is the question and I'll share that coming up in another post at some point.