12.5mm Docter Eyepiece

[Don Pensack]

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.

[ausastronomer (John Bambury)]

Hi Don,

Excellent post.

That now puts things into better perspective and most importantly highlights the subjective areas which are most important to you and in many cases are less important to other observers.

I don't like the AMD, but like I said, people who primarily view at the center won't notice it.

The above is a classic case of this. Whilst I don't like eyepieces which are not sharp right across the field, AMD is obviously less important to me. I always try to observe with the target properly centred in the FOV as there hasn't been a telescope invented yet that will give identical image quality at and near the EOF, as it gives on axis. My 3 main dobs all have tracking and I continually keep the target centred in the FOV. I also use a paracorr. I have another 10" dob which does not have tracking, but I always hand track with it to keep the target centred in the FOV. I laugh when I see people recommending to others to observe in sub F6 dobs, without a paracorr, using the drift method. In this scenario irrespective of how good the optics in the telescope are, image quality towards the EOF will be less than 1/2 wave due to comatic blur and it gets a whole lot worse as the eyepiece focal length increases.

I knew you were calling this as you saw it and not letting your business interests cloud your judgement, but you just see it differently to me and many others, as you place a lower emphasis on points which are more important to others and vice versa.

BTW You and Pam need to get back down here again for another Ozsky. 2016 was fully booked a month after April 2015 finished, but you should book in for 2017; or do you need to sell more Naglers first

Cheers,
John B

[simmo]

[wavelandscott (Scott)]

One of the interesting (to me) things about this thread is that in the end it reinforces that there really is no single "best of" eyepiece that is perfect.

Like many things, the answer to what might be "best" is dependent upon many factors and in this case differing preferences. For those looking for their own "best" piece of eyepiece gear, there is no substitute for experience with a variety brands and designs. Get out under the stars, use what you have and learn what you like and then choose appropriately.

Clear Dark Skies to all!

[FlashDrive (Poppy)]

Originally Posted by wavelandscott

One of the interesting (to me) things about this thread is that in the end it reinforces that there really is no single "best of" eyepiece that is perfect.

Like many things, the answer to what might be "best" is dependent upon many factors and in this case differing preferences. For those looking for their own "best" piece of eyepiece gear, there is no substitute for experience with a variety brands and designs. Get out under the stars, use what you have and learn what you like and then choose appropriately.

Clear Dark Skies to all!

Spot On

Col.

[N1 (Mirko)]

Someone has done a quick comparison between a Baader Morpheus and a Docter UWA (among others) in the field, post #1174939:

http://forum.astronomie.de/phpapps/u...76#Post1171737

Use Google Translate.

[ab1963 (Andrew)]

I think that it is important to mention that the man Alex who did the review on some level works for Baader I believe as one of the posts that comes up in response states,i think that is something to take into consideration

[N1 (Mirko)]

Originally Posted by ab1963

I think that it is important to mention that the man Alex who did the review on some level works for Baader I believe as one of the posts that comes up in response states,i think that is something to take into consideration

Yes, someone did point that out further down in the same thread, and Alex replies that he is some sort of freelance reviewer whose customers include, but are not limited, to Baader Planetarium.

[ab1963 (Andrew)]

but has no affiliation with televue or docter so makes the point important

[clive milne]

Originally Posted by wavelandscott

One of the interesting (to me) things about this thread is that in the end it reinforces that there really is no single "best of" eyepiece that is perfect.

I agree.

I find it interesting that the Nagler T6 should be offered up as a benchmark.

I have found it to be a singularly unimpressive design to the extent that I wouldn't consider purchasing one at any price that would be conceivably profitable for the manufacturer.

The T4 on the other hand ticks a lot of boxes for me.

Is the T4 eminently superior to the T6? Not at all.
Clearly, there is a physiological component to the merit function of eyepiece design which is difficult to quantify.

And let's be frank... on any given night, there is an order of magnitude less variation in the qualitative visual experience across the gamut of potentially competitive eyepiece choices than you will find as a result of other factors too numerous to list.... (which I wont, given my current level of dgaf)