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Well, John is right. I am a TeleVue Vendor and not a Docter vendor.
I had heard so much praise for this eyepiece that I jumped at the chance to use it, and I anticipated I would be impressed.
I suppose I should state that I agree with the contention that angular magnification distortion is a bad thing in astronomical observation, whereas a fairly high degree of rectilinear distortion is easily tolerated. A good example of this is the 24mm Panoptic, which gets a lot of praise, but has a ton of RD. Those who cannot tolerate RD don't like that eyepiece.
And the Docter definitely has AMD at the edge. More than other eyepieces I have used (316 personal eyepieces as of this writing) in a telescope at night. I have, however, seen this in many many binocular eyepieces, and it doesn't surprise me that the Docter is supposed to have binocular use as its heritage.
As a cautionary note, I would also comment that I have only used the Docter for about a half hour on about 4 separate targets. And the comparable eyepieces used as test subjects were the 14mm Vixen SSW and the 13mm TeleVue Nagler T6. My comments were from my notes made during their uses and in the immediate comparison as the eyepieces were switched back and forth.
I also note that I do not like long eye relief eyepieces in short focal lengths, preferring eye reliefs of 10-13mm. I do not view with glasses. If the eyepiece has an adjustable eyecup, though, I can usually dial it in so the long eye relief doesn't become an impediment to viewing. The Docter had a long eye relief compared to the other 2, which, while ideal for a glasses wearer, was, for me, a factor that made the eyepiece harder to use.
Those of you who dive into optics know that it is not possible to simultaneously solve both RD and AMD in widefield eyepieces. They either will have one or the other or a bit of both, depending on the point of view of the designer. Generally, RD is thought to be bad for daytime views because it distorts straight lines near the edge of the field, and AMD is thought to be bad in astronomical use because it distorts shapes and separations as objects near the edge.
If the target is held in the center, either form of distortion will be unnoticeable. If, on the other hand, you let the target drift through the field (common in dobs), then distortion will be noticeable and it is likely AMD will be more objectionable.
TeleVue regards AMD as the form of distortion to be limited (so do other eyepiece makers). And the Ethos eyepieces have less than 1% AMD anywhere in the field. Since they have wide fields (100-110 degrees), that means that, because they cannot void the laws of physics, those eyepieces have a lot of RD, regardless of what scope they are used in.
I did not find the Docter to have notable astigmatism, lateral color, or spherical aberration. It is a sharp eyepiece. One of the targets was a planetary with a magnitude 15.9 central star (fairly hard to hold with direct vision on a reduced transparency night). It was about the same in both the T6 and the Docter. As was the view of the planetary itself.
Resolution on a globular (M15) was about equal, with the core resolving into a mass of tiny little pinpoints in each eyepiece--even the Vixen, which was the 3rd place eyepiece in the test because of lateral astigmatism and a slightly curved focal plane. Plus, the Vixen had eye placement issues due to a distortion of the exit pupil that made the eyepiece very hard to use.
The Docter was only hard for me to use because of its long eye relief and the shape of its eyecup. I noticed no exit pupil issues.
I contend it is primarily in the outer 50% of the field that differences between eyepieces show up. And some issues there can be overcome for a particular observer if other characteristics, such as eye relief, or rendition of colors, or other things are more favorable for that observer.
I am an amateur astronomer first, and like most of us, I have my likes and dislikes. The first thing I do when I put an eyepiece in my scope is to focus, then look at the edge. It is where the differences lie. Sure, other things are important, too, but for me, edge astigmatism or EOFB automatically disqualifies an eyepiece for me as a possible purchase. Strong field curvature I cannot accommodate also removes an eyepiece from consideration. The Docter has none of those.
Other observers might first look at eye relief, or contrast in the image, or apparent field, or overall sharpness of the star images (if you are blessed with good seeing), and I look at those things too. The Docter, to my eye, is an excellent eyepiece in many regards, but I still feel it is not superior to the T6 Nagler. And definitely not to the Ethos. That some people think so may be a reaction against the larger FOV of the Ethos, or its reduced eye relief, or its size and weight, IMO, and not likely due to its optical image quality.
I will view with my friend again in the future, and I will take another look at the Docter in my scope. I don't like the AMD, but like I said, people who primarily view at the center won't notice it.
I want to state, however, that my inventory does not influence my opinions. There are many fine eyepieces I don't sell, but think quite highly of (Pentax XW, Nikon NAV-HW, etc.). When i post, I post as an amateur astronomer, not as a dealer. You will never see me "pimp" a particular product.
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