Telescope Reviews: Second Annual World Cup: Eyepieces

Well, I was gonna reserve the preaching for the next post, but I think we're coming dangerously close to getting wrapped around the axle here; too buried in semantics, technicalities and minutiae.

Last year, the World Cup was originally pitched as the "First Annual Eyepiece Resolution World Cup". Use of the term "Resolution" in connection with the test format, criteria, eyepiece and target selection, generated what seemed like seven hundred posts agonizing over whether our results would really be measuring contrast rather than resolution, or rather sharpness instead of contrast or resolution, or perhaps a combination of sharpness and contrast with a little transmission thrown in rather than resolution, or...You get the idea.

Deep breath. Let's stop wringing our hands. Smile. Be happy.

Okay. In deference to such concerns, last year we re-titled the exercise "Eyepiece resolution(TM) World Cup" and explained:

"(B) Semantics.

We originally titled this evaluation "The Eyepiece Resolution World Cup." Use of the term "resolution" drew considerable criticism. Several knowledgeable observers posited that seeing Trapezium E and F in theory would not really be a test for resolution. A 4-inch scope ought to be able to resolve targets with such wide separations as the A-E and C-F separations no matter what 7mm to 8mm eyepiece is used. It was suggested that we supplement the field testing with daytime testing using white-on-black USAF resolution targets or with currency. We discussed this, but declined to pursue such testing for reasons discussed below.

Rather than resolution it was also variously suggested that our evaluation might technically instead be showing contrast, sharpness, or some other characteristic that might or might not be related to resolution. My own feeling is that testing eyepieces for isolated characteristics like sharpness, contrast and resolution in a laboratory is fine if you want to know what those things look like in isolation, in a laboratory. Unfortunately (or fortunately, depending on your perspective) few of us spend much observing time in a laboratory looking at laboratory type targets. In the field at night with dynamic conditions, luminous targets, inconsistent backgrounds, inconsistent luminosities, etc., I find it very difficult to ascertain whether I’m able to pick out a detail in one eyepiece but not in another because (a) my eyepiece has superior resolution, or (b) my eyepiece has superior sharpness, or (c) my eyepiece has superior contrast, or (d) a combination of one or more of these characteristics, or perhaps due to some other factors entirely.

Rather than try to attempt what Dan and I didn’t feel we were competent to or patient enough to complete, we instead made a decision to revise the title of the article and substitute "resolution™" for "Resolution". Rather than trying to determine which characteristic in a strict, technical sense was responsible for showing us more, we instead chose to go with the plain English meaning of "resolution" rather than the technical and scientific meaning. Ironically certain dictionary definitions of "resolution" resort to other terms like sharpness. In any case, for purposes of this report "resolution™" shall simply mean "the act or process of separating the Trapezium into constituent parts." That is rather than a characteristic of the eyepiece, the term describes the action of using the eyepiece to accomplish the stated task. We’ll say what we were able to see using each eyepiece on the chosen target. We’ll leave it up to you, the reader, to speculate on why we were able to see more using some eyepieces than others..."

To further elaborate, let's dig a little into the dichotomy of theory on one hand and practice on the other. In "theory" a 4-inch scope operating at 110x to 127x should have *no* trouble at all pulling in Tarpezium A-F provided that seeing and transparency cooperate. In "practice", one can read countless posts of in the Double Stars forum and elsewhere on CN where verteran and beginning observers alike struggle to pull in Trapezium F in 4- to 6-inch scopes. In the dry run of our own testing last year, we used a 6" refractor to test out a few of the eyepieces and were dismayed that the 6-incher pulled in only A-D under sloppy seeing conditions. Fortunately the conditions were much better two days later when we conducted the comparisons, but I think this illustrates what I mean by theory vs. practice.

Let's also look at the "World Cup" connection. There are probably few sporting events on the planet that compare to the World Cup in terms of consternation about fairness of match-ups, allegations of fraud and favoritism among the organizers, and raw emotion. Nationalism and sports fanaticism combine. In World Cup play, it doesn't matter that on game day it rains and the pitch is a soggy tragedy, or that France's star Zidane is allergic to mustard pollen and there's a field of mustard adjacent to the football facility. The game goes on and rarely does the worse team better the superior team, despite all of the things that "could have been better."

Next point. This is supposed to as much about fun as it is about gear. If you want clinical scientific reports, worried to dog-earedness and cross-referenced to to an encyclopedic bibliography, write them. The Eyepiece Hooligan and his mates can't and more importantly don't want to author such reports. There's little joy in them, and as a result the relevance to the majority of of observers is suspect.

Our targets need to be moderately challenging for the atmospheric variability, aperture and magnifications used. In the field, unlike in the basement, the number of variables that materially impact what is seen in the eyepiece is staggering. In practice, I've found that tasks which in theory ought to be accomplished comparably and handily by a given scope using a given magnification range, aren't, and that no matter how many times you try one lower magnification eyepiece consistently outperforms another higher magnification eyepiece, on-axis, on targets such as those being discussed for the World Cup. I don't know why. I could speculate, but don't feel the need to do so. I don't really care "why". I'm only after the "what" as in "what did eyepiece x show that eyepiece y could not". I'll leave the "why" to the more genteel and scholarly among us. Oh, and I promise I won't beat you up in the hall and take your milk money. I grew out of that long ago.

Kidding of course. I had my milk money taken quite a few times actually.

So with that in mind, we're sticking with a mix of 4mm and 5mm eyepieces. We're looking for moderately challenging double stars (3 of 'em) for the aperture and magnification range described. We're hoping for decent seeing. We understand that there are flaws in the methods, flaws in the theory, and flaws in the socio-economic and cultural systems that sustain folks such as ourselves when there are species disappearing, children starving and ice caps melting. Nonetheless we ernestly hope that you enjoy our second little bit of "fluff" when we publish it.

Oh and as for BIG DOBs, I've honestly never looked through a Dob larger than about 12" that threw up anything but slightly soft, mushy, unsatisfying-compared-to-a-regractor stellar views. Probably a combination of miscollimation and lack of adequate cooling, but that's my experience. I know that sharp stellar views in Dobs exist. If the little'uns can do it, there's no reason the big'uns can't, but that's my experience and resulting bias. Also I don't think I'm alone. For example, in Sissy Haas' double star field guide "Double Stars for Small Telescopes: More Than 2,100 Stellar Gems for Backyard Observers," Sissy uses a refractor for most of her observations. Other observers she references use scopes up to about 12" of various designs. For some reason, however, very few of the reported observations were made using a big Dob. Surely these "pros" could afford whatever scope they wanted for their double star work. In fact an 18" to 20" premium Dob is no more (and likely less) expensive than a premium 5" to 6" refractor on a premium GEM.

Perhaps I am being a bit provincial, but I think there's actually value in NOT resorting to larger aperture reflectors for this particular comparo.

Surely I'll be consumed by a pillar of fire or something for saying so, but hopefully it won't be until after we've finished the testing.

Regards,

Jim

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"I do not know what I may appear to the world; but to myself I seem to have been only like a boy playing on the seashore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me."

- Sir Issac Newton

Edited by jrbarnett (11/03/09 11:35 AM)