Sunday, September 25, 2011

 

The Ultra-wide Revolution


Unless you’re such a committed (in more ways than one) astrophotographer or astro-videographer that you never do any visual observing at all, eyepieces are a fact of life. And for better or worse, muchachos, many Joe and Jane Amateur Astronomers determine the worth of an eyepiece by its apparent field of view. In other words, today wide fields = good, narrow fields = bad. Whether you think that is wise or not, the big AFOV 82-degree plus “ultra-wide” oculars rule the roost in the hearts of most amateurs.

What brought this subject to mind? The brouhaha engendered by the release of Explore Scientific’s new 120-degree apparent field 9mm eyepiece. Oh, how an eyepiece no one had seen—much less used—was condemned. Too much field. Why would we ever need that much? Hell, 30-degrees of apparent field via a Ramsden was good enough for us back in the day; why should things be different now? Too expensive. A grand for a fracking eyepiece? COME ON!

I suspect the same things motivate the naysayers as last time this became an issue, when Unk Al released the first of his Ethos oculars. For some folks it just seems like too much of everything. There is a thread of Puritanism running through Americans that insists there’s always a piper to be paid. Unk mentioning that folks pay far more than the 900 bucks Scott Roberts and company will be charging for the 120 on far more ephemeral things like big screen TVs and four-wheelers doesn’t do pea-turkey to change these worthies’ minds.

“But how about all that field, Unk? Aren’t they really right about that? Do we really need 120-degrees worth?” Do we need 100? How about 80? How about 50? The size of an eyepiece’s apparent field does not necessarily determine its quality, no, but for some observers it does determine how comfortable an eyepiece of any quality is to use. I am one of those people. I’d no sooner go back to peering through the soda-straw hole of a Ramsden or a Kellner than I would go back to (trying) to image M101 on a roll of Tri-X film.

But, in typical Unk fashion, that is putting the consarned cart before the horse. Where did these fancy-dan EXPENSIVE eyepieces come from? What is this “apparent field” business all about, anyhow?

My eyepiece story begins, not surprisingly, with my first telescope, a 3-inch Tasco Newtonian Daddy got me after I’d been begging for a scope for 6-months. This “instrument” was bought in the pawn shop of a buddy of his. Actually, Daddy probably traded his expertise at TV repair for the pretty little thing. Not that it looked little to me. It was smaller than the huge stove-pipe of an f/12 6-inch we’d borrowed for a while, but it was big enough, little Rod thought, and looked oh, so much better than the home-built scope, with a gleaming white tube and a beautiful wooden tripod.

Alas, this telescope never lived up to its appearance. The Moon looked pretty good and deep sky objects were acceptable within the bounds of what can be expected from a 3-inch telescope from a somewhat (though not yet badly) light polluted 1960s suburban backyard. The planets, Jupiter, Saturn, and Mars? Blobs. I’ve often wondered what the problem was. The mirror was likely a sphere, but at f/10 or so it should have been OK if it was even halfway competently made. It’s possible the mirror clips held it too tightly in its cell and I didn’t know enough to check that. Prime suspect then and now, or at least a contributor? The nasty little eyepieces.

The Tasco didn’t come with many accessories. Hell, it didn’t even have a finder; just a couple of perforated metal tabs that served as a peep-sight. But it did feature a pair of eyepieces, an 18mm and a 10mm I recall. These were Huygenians, two-element eyepieces as simple as an eyepiece can get and still be worthy of that name. Barely. They were not only simple; they were small—.965” barrel diameter Japanese standard oculars. That came to spell “junk” for me, though that was not always true even then. Not only were these oculars’ eye lenses small, I had to really jam my peeper up against them to see the whole field, which even to my inexperienced eye seemed tiny. Despite these things, I didn’t give the eyepieces too much thought at first, blaming my sorrows on a bad mirror.

The more I read and learned about telescopes, though, the more I began to suspect the eyepieces (I now knew enough to call them “eyepieces” instead of “lenses” thanks to my mentor Patrick Moore). The Christmas after I got the scope, I asked Santa to bring me a new ocular. Daddy helped Santa by showing him the catalog from this company he’d heard about, Edmund Scientific. I asked for HIGH POWER, a 6mm .965 Ramsden that was within the Jolly Old Elf’s price range. I’d probably have been smarter to ask for low power, but how was I supposed to know that? All I knew was the eyepieces I had didn’t show me much of the planets, and maybe more magnification would help.

Ha! As I think I kinda expected, the Ramsden (nearly as simple and cheap as a Huygenian) gave images that were like something that came out of the wrong end of Aunt Lulu’s poodle dog. I gave up my bad eyepiece theory and went back to blaming the primary. The denouement? When I got my wonderful Palomar Junior, I fashioned a .965”- 1.25” adapter out of a cardboard tube and tried the 6mm in the new scope. The images were nearly as horrible as they had been in the Tasco; maybe the eyepieces had been at fault after all. Not that it mattered; the 3-inch was long gone, sold to help finance My Pal.

Experience has taught me that Uncle Al Nagler is right when he says the eyepiece is as important as the mirror or objective lens. I actually figured that out on my own; it just took me a few years. I progressed slowly, ever so slowly, moving from war-surplus-optics Ramsdens and Kellners like those that came with the Palomar Junior, and which I thought were incredibly good—and were incredibly good compared to the Huygenians that came with the Tasco—to the More Better Gooder.

The first eyepiece that showed me what an eyepiece could be? Somehow, someway one of my fellow members in our little teenage club, The Backyard Astronomy Society, acquired a special new ocular, an Erfle, just before the club broke up for good toward the end of high school. I’d never really understood what the books meant by “Apparent Field of View” till I looked into this thing. Going from the keyhole of a 35-degree AFOV Ramsden to the picture window of a 70-degree AFOV Erfle was a revelation. No, it was more than a revelation; it was a REVOLUTION. I had to get me one of them things. If only they weren't so danged expensive.

Before we go further, I need to ‘splain something to the greenhorns round here, “Apparent Field of View,” which seems to be a difficult concept for some novices to wrap their heads around. The least confusing way I’ve found to describe it? Consider television sets. Larger versus smaller apparent field is (somewhat) analogous to viewing The Andy Griffith Show on a 12-inch portable compared to a 60-inch big screen. You see the same vista of Mayberry, but in wider, far more expansive fashion on the big screen job.

This analogy ain’t perfect. Since the true field of a telescope, the amount of actual sky it takes in, is dictated in part by the size of the apparent field (true field of a telescope equals apparent field divided by magnification), the actual expanse of sky, the true field delivered by a wide apparent field ocular, will be greater, too, but I still think the comparison is purty apt. The benefit of large apparent field is that the eyepiece field circle, the “screen,” is larger and more comfortable to view. It is, as Uncle Al has always said, the spacewalk experience.

Big AFOV is always better, then, right? Not always. If there’s not enough eye-relief to let you see all of it comfortably, what good is it? “Eye relief” is the maximum distance you can hold your eye from an ocular’s eye lens and still take in the whole field, and is almost as important a specification (especially if you must wear glasses to observe) as eyepiece focal length or apparent field. I had to jam my eye up against my Huygenians because of their lack of eye relief.

I didn’t completely desert narrow field eyepieces after that first look through an Erfle. There were those narrow AFOV but much lusted after (in the 1960s) Orthoscopics that I was finally able to afford as the seventies came in. By the time I’d moved from my last homebrew 6-inch to a Cave Newtonian and, shortly thereafter, my first C8, I was observing, like many “advanced amateurs” (that’s what we called ourselves, anyway), with a combination of Erfles for low power/deep sky work and Orthos for high power/planetary viewing. And we and I were perfectly happy with that. Till everything changed.

What changed? The SCT revolution of the 1970s was followed by the Dobsonian revolution of the 1980s. With (almost) everybody going to large and thus relatively long focal length Newtonians on undriven alt-azimuth mounts, the idea of eyepieces with large apparent fields of view had real appeal. Big portholes on space would mean you wouldn’t have to nudge the scope as often as with narrow AFOV oculars. It was also true that the big telescopes were showing us the beauty of the deep sky in a way we’d never seen before, and bigger windows on the Great Out There would, we figured, allow them to show us even more of the majesty of deep space.

Sometimes the stars all align the right way, and that’s what happened in the 1980s. We wanted wider apparent fields and Al Nagler was there. Unk Al began his business, TeleVue, in 1977 selling very good Plossls (and lenses for the projection TVs they had in the freaking discos), but didn’t stand still. In 1980, TeleVue debuted the eyepiece that changed visual amateur astronomy forever, the 82-degree AFOV 13mm Nagler.

Sure, there had been ultra-wide field eyepiece designs before the Nagler, but not one that not only delivered that huge amount of space, but whose other characteristics were so good that the eyepiece was a joy to use in our fast new Dobbies. Despite its quantum leap in apparent field, the Nagler’s images were worlds better in f/4.5 – 5 telescopes than those of the Erfles, which could be horrible at low focal ratios.

What did Unk Rod think of the Naglers? I thought they were expensive. They were probably the most expensive eyepieces I’d ever heard tell of, with the 13 going for a solar plexus punching $250, equivalent to at least 600 of our smaller 21st century dollars. I didn’t think much more than that till I got a look through one at a star party. Then they became spoilers.

They were spoilers in that they spoiled my eyepiece collection. No amount of rationalization could make me happy with the keyhole/soda straw experience of Orthos or even those (for me) newfangled Plossls. My Erfles just depressed me. I resisted for some time, but eventually gave in to the urge for ultra-wide viewing. Miss Dorothy got me a 12mm Nagler Type II on one of our first Christmases together, and I never looked back.

I loved the 12mm Type II and used it happily until just a few years ago. I didn’t rush out and buy a boxful of Naglers, though. I am a stingy sort, and was able to use my one Nag happily with the aid of a TeleVue Big Barlow and a Celestron f/6.3 reducer corrector for just about everything. It would have been nice to have a longer focal length Nagler to use in my Dob, Old Betsy, though.

Just when I was fixing to fill my case with Naglers (and empty my bank account in the process), I discovered the Uwans. The William Optics Uwans (“Ultra-wide Angle”) came in from China early in this century, and were a sign, if we needed one, that Chinese optical competence was improving by leaps and bounds. They’d gone from early, pretty putrid ultra-wides to eyepieces that were actually better than Naglers at some focal lengths. Unfortunately, these eyepieces, which are now also available from Orion, where they are called the “MegaViews,” have never expanded beyond the initial line-up of 28mm, 16mm, 7mm, and 4mm focal lengths. Nevertheless, I was happy with the Uwans until, a couple of years ago when everything changed again.

I was aware of TeleVue’s new 100-degree AFOV marvel, the Ethos. How could anyone even on the periphery of amateur astronomy not be? But that was not the same as getting a look through one. When my good buddy Pat and I were able to borrow one for a few minutes one beautiful winter’s night on the old field at the Chiefland Astronomy Village, the 13mm, and I got a look at M42, the deal was sealed. My bank account would suffer. Badly. To the tune of about 600 bucks, which was, as when the Nagler bowed in, more than I ever dreamed of paying for any ocular.

What I loved and still love about the Ethoses is not just that 100-degree apparent field, which fulfills all my spacewalk dreams, but the fact that that aside they are just damned good eyepieces. Mechanically, the Es are very finely done, as you’d expect, if big and heavy, as you’d also expect. Optically? The sharpness and contrast they display is incredible. Despite the 13mm’s much wider field, it is better in these respects than my much loved 12mm (which soon went to the Astromart). Edge of field? Free from aberrations and bee-you-ti-ful.

Which don’t mean, of course, that the eyepiece won’t display coma in a fast telescope. Some newbies and some not so newbies wonder if very expensive, very good eyepieces will dispel the coma comets. The answer is “no.” I know of no eyepiece with a built-in coma corrector, which is what would be needed to do that. Good eyepieces like the Ethoses can reduce other aberrations—like astigmatism—and make the edge look better than it would with a less capable eyepiece, however.

So here’s where I stand now: Ethoses, the 8mm and 13mm models, and my 7mm, 16mm, and 28mm Uwans (I still like my Panoptics, too). Why haven’t I pressed on to the 21mm Ethos? I tried the very similar Explore Scientific 20mm 100-degree jobber-doo at Chiefland one evening, and decided neither it nor the equivalent Ethos would be useful for me. The eyepiece vignetted in my SCT with the f/6.3 reducer in place. Not bad, but quite noticeable. The field was cut off before it was supposed to be. And I have no doubt the 20 E would do the same. I can stand a little vignetting, but there didn’t seem to be any need to.

Thing is, I can get as much field as the 20/21 offer at f/10 with my 13mm and an f/6.3 reducer-corrector. The 13mm works great with the r/c or a Denkmeier reducer in my CATs. So, not much incentive to break the piggy bank again. Not that either eyepiece is not wonderful. If I used my Dobsonian, Old Betsy, more often, I’d have one or the other.

So, you’re a novice who thinks this space walking stuff sounds like fun? Or you are an old hand who has finally been convinced that the ultra-wides might offer an experience noticeably better than that of Plossls and Orthoscopics, and maybe even put some fun back in visual observing? What do you do? You could buy a caseful of Naglers and Ethoses. Can’t go wrong there.

But, yeah, I know not everybody is willing to jump into the deep end of the pool right off the bat. You can’t go wrong by buying the best eyepieces available, no, but there are some interesting ultra-wide alternatives that won’t hurt quite as bad moola-wise as TeleVues. In some cases these eyepieces can even offer, like the Uwans, not just “nearly as good,” but “better.”

The Uwans

Yeah, the Uwans were a surprise for me. Hell, they near about bowled me over with their quality and utility. You would have to go a long way to best the 16mm model, especially. I love all these oculars, which feature truly useful integral eye-shield/cups and beautiful coatings, and that is tempered only somewhat by the afore-mentioned lack of focal lengths. The prices ain’t bad, either. The top of the line 28mm, which compares very favorably to the 31mm Nagler, is $399 vice over $550 for the TV.

You can actually go even lower in price than the Uwans or the Meade Series 5000s (below) and still get 82-degrees, but you won’t be overly happy with the result. Chinese import eyepieces like the Owl Astronomy Ultra-wide Angles can give you a taste of spacewalking, but don’t expect the field edge in a faster scope to be anything to write home about. In fact, depending on you and your scope, it may not even approach acceptable. Alas, in the ultra-wide game, it is still TAANSTAFL—there ain’t no such thing as a free lunch.

The Meade Series 5000 Ultra Wide Angles

Not long after Uncle Al established the Naglers as a whole line of eyepieces, Meade, in a fit of expansion fever, came out with their own “Naglers,” the Ultra Wide Angles. Some folks looked down on these eyepieces as mere “clones,” but since Al and company didn’t complain, I didn’t see any reason for me to, either. If nothing else, the Meades were available in slightly different focal lengths and were also (slightly) less expensive. These oculars have their fans, then and now, and can certainly perform well in any scope for a fare a little lower than the Nags.

About five years ago, Meade was still booming and had just released their ill-fated RCX SCT scopes. At this time, they also updated the Ultra Wides. This refresh mostly consisted of new bodies for the oculars, snazzy things that looked a lot like Celestron’s Axiom ultras (a line which, while Unk doesn’t know much about it, is rumored to be good and might stand some investigation on your part). Unfortunately, while the “new” eyepieces looked modern, these new bodies were not well thought-out.

The prime offense was that they incorporated hard, built-in eyecups, just like the Uwans. Twist to raise, twist to lower. Thanks to the kindness of a Meade rep, I was checking one of these out at the 2006 Cherry Springs Star Party, where I was a speaker. Extended the eye-shield. Purty cool images. Then I grabbed the barrel to remove the eyepiece from the scope, and encountered the dreaded Chinese glue-grease (weasel fat based, I reckon) when I touched the section of barrel exposed by extending the eyecup. Had a hell of a time getting the stuff off, and it made me appreciate TeleVue’s attention to detail all the more.

Explore Scientific Ultra Wides

Everybody and his sister knows about Explore Scientific (Scott Roberts’ “new” company) and their 100-degree wonders, but did you know they produce 82s as well? I suppose I knew they did, but didn’t know much about them till my buddy Pat showed me one at the PSAS dark site a little while back.

Verdict? A hit. At least as good as a Uwan, and, while I haven’t done a shootout, the eyepiece and those I’ve had the opportunity to try since, are close to the Naglers in my opinion. You even get “nitrogen purged,” just like the ES 100s. The “82 Series” oculars are available in seven focal lengths from 4.7 to 30mm, and are insanely nicely priced, ranging from $99.95 on the low end to $249.95 on the high end. If they are all as good as the couple of focal lengths I’ve tried, the operative word is B-A-R-G-A-I-N.

But what made Explore a household name (in amateur astronomy households) was their Ethos competitor, the “100 Series.” I have little doubt you would be happy with any of these, the 9mm, the 14mm, or the 20mm. Their images are, to my eyes, indistinguishable from those of the Ethoses. AND…they are not only available in slightly different focal lengths, they are significantly less expensive, with the most costly, the 20, going for a startlingly reasonable $399.95. If I didn’t have the 8mm and 13mm Ethoses, I’d have the 9 and 14 ESes. Does everybody agree with Unk that these eyepieces are as good at the Ethoses? No, but I can only report what I experience, muchachos, and even those who think the Es are better admit the difference is SLIGHT.

You may be wondering about one of the ES 82 and 100 features, the nitrogen purging business. What’s that for? Hard to say. The eyepieces are certainly waterproof, with Mr. Scott demonstrating that at NEAF one time by dipping a 100 in a fish tank. But what good is it? I’ve never dropped an ocular in a fish pond, and I’ve never had a problem with moisture inside my TeleVues, even in the muggy ‘Swamp, but I suppose the nitrogen might help prevent or reduce internal fogging. Maybe.

It was not the ES 100s that inspired this article; however, it was their new 120. This eyepiece, with a field bigger even than TeleVue’s 110-degree 3.7mm Ethos SX, a focal length longer and more useful than the SX at 9mm, and a price higher than any TV at a projected $999.95, naturally inspired much heated discussion on the Cloudy Nights by eyepiece Luddites. Same old same old: we don’t need all that field. It’s too expensive.

What does Unk think? At first I was inclined to agree with the naysayers. But then I started cogitating. Let’s face it, you WILL notice an increase in apparent field from 100 to 120, and a 9mm eyepiece would, in my CATs, give both a huge picture window and plenty of magnification to reveal detail in small objects. It would also probably perform like a champ at f/6.3, yielding the equivalent of a 15mm eyepiece. A 15mm with 120-degrees of AFOV. You can bet that gave Unk pause. If only he had an extra grand lying around, he’d get him one of these argon purged wonders. I don’t know that is likely to happen anytime soon, but if it does, I’ll let you-all know. Hell, you can be sure I’ll let you know as soon as I even get a look through one.

And there you have it. The ultra-wide story, at least as remembered by Unk. If you insist on clinging to your soda-straw Zeiss Orthos and Tak LEs and Claves or whatever else floats your eyepiece boat, good on ya. Just don’t expect Unk to be there with you. He is a field-o-holic and will likely remain one.

Next time: The Revenge of Astroplanner!

Comments:
Thanks for the heads-up, Uncle Rod! I actually did not know about this 120-deg. ocular.

What I notice is that the 120-deg. 9 mm should give almost twice the area of the sky at essentially the same magnification as the 8-mm Ethos. This combination of magnificatiopn and field sounds appealing for some of my observing. I guess I will be getting one.

Yet for certain other kinds of observing, including deep-sky, I will "insist on clinging" not only to my Zeiss orthoscopics, but - horror! - also to my 30-degree monocentrics. Perhaps the only thing better than the expansive field of view is an expansive selection of observing tools. These are great times for visual astronomy. Yours, Ivan
 
Hi Unk, Great entry. I await your blog like I await S&T coming in the mail.

Just wanted to throw a correction your way. The ES 82 line has 8 FLs not 7. 4.7,6.7,8.8,11,14,18,24,&30. The 8.8mm just came out in August, way after the other ones.

I got into the hobby about 10 months ago and got serious in April. These ES oculars allowed me to fill my EP case with premium glass (8.8,11,14,24mms) for the price of 2 Naglers. What a deal! Highly recommended.

Yours,
Eddy
 
Speaking of field of view, I had a question regarding visual backs. I am using the stock visual back that came with my CPC1100. Can I increase my FOV by substituting a different visual back on my scope? Thanks for all of the great information Rod. Your books have helped me immensely, both in selecting my scope and in getting the most enjoyment out of it!
 
Hi Uncle Rod,

Just giving my 2 cents worth. My astro budget is tight. I can't afford these expensive e.p. I just returned from the Okie-Tex Star Party where I viewed ngc 247 with my 20cm LX-90. I located it with my 32mm plossl and then popped in my 15mm plossl and it looked real nice. A neibor had a 25cm LX-200 and a nagler 12mm I think, it was barely detectable. I'll stick with my Plossl's for now. I have a 38mm Q70 and know from experience that my Plossl's go deeper.
 
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