by Ed Ting
TeleVue Naglers - 22mm Type 4, 13 mm Type 6, 7 mm Type 1 (foreground), 13 mm Type 1, 31 mm Type 5
In the early 1980's, Al Nagler created a small sensation when these eyepieces were introduced. Larger and far more expensive than anything which had previously hit the market, the Naglers changed the way astron- omers viewed the skies above us. What's so special about Nagler eyepieces? Consider: the human eye can only take in about a 50 degree field of view, comfortably (you can see more with peripheral vision, but 50 degrees is about what you can hold in you view at one time and still concentrate on everything.) As a result, most eyepiece designers stayed within this 50 degree limit. Many eyepiece designs, like Kellners (and their offshoots, MA, RKE, etc), and even good Orthoscopics are limited to 40-45 degree fields of view. After all, what's the sense in making an eyepiece with a FOV that's more than the eye can handle?
Al Nagler, a former optical designer* who worked on various flight simulators, came up with a large, complicated design that provides the viewer with an astounding 110 degree FOV. His goal was to create a "spacewalk" feeling when looking through these eyepieces. This is accomplished by sticking a barlow-like lens group inside the barrel of a long focal length eyepiece. As a result, the eyepiece maintains a much larger "eye lens" (the one you look through) and a much longer eye relief than you would expect from the given focal lengths.
(* Note: Al wishes to express that he is STILL an optical designer, just one not working for NASA any more!)
For example, the 9 mm Nagler has an eye lens about .75" in diameter and an eye relief of about 13 mm. These are figures comparable to a standard 20 mm Plossl. In other words, if you crave medium-to-high power views but hate little eyepieces with teeny-tiny lenses and short-short relief, the Naglers are for you. The end result is that you cannot physically take in the whole FOV at once. You have to move your eye (and sometimes your whole head) around to see it all. On the 4.8 mm and 7 mm, you may not be able to find the field stop at all (you DEFINITELY will not find it if you wear glasses while observing.) Watch someone looking through one of these eyepieces sometime. You will see them turning their heads, apparently looking at the inside of the eyepiece barrel. I describe this sensation as "falling" into the FOV; it seems like an alternate reality that goes on and on (can't attest to how it compares to a real space walk!)
There are other benefits as well. Previous wide-field designs (like Erfles) were able to squeeze out a 60-70 degree FOV, but at the expense of sharpness at the edges of the field. The Naglers, on the other hand, are sharp practically to the field stop (and the field stop is not always easy to find!) Also, the extremely wide FOV has a benefit to telescope owners without clock drives. You don't have to move your scope as often, since you're looking at so much sky. As an example, take your typical 6" f/8 reflector owner who's currently using a 40 degree FOV 25 mm Kellner eyepiece. This setup yields a true FOV (what you're seeing in the sky) of about .82 degrees. The same telescope with an 82 degree FOV 13 mm Nagler will yield a .875 degree true FOV. That's right, the 13 mm Nagler, despite yielding twice the magnification of the Kellner, will STILL show you more of the sky! Put another way, the Nagler 13 will show you twice as much sky as a typical 12 mm Kellner.
The 13 mm, by the way, is a truly astonishing eyepiece. At 1.6 lbs and almost 5.5" tall, it is referred to as "the grenade" by several observers (the Nagler 20 mm Type 2 and Panoptic 35 mm also share this epithet.)
Drawbacks? A few. First, the obvious: size and weight. Some telescopes and drive mechanisms can't take the weight. Switching between, say, the 20 mm Type 2 and the 7 mm may require you to rebalance your scope. This can become a pain REAL FAST. If you have gone through this, you know what I'm talking about. Note: recently, TeleVue has introduced a brass "equalizer" device that allows you to match weights between your 1.25" and 2" eyepieces. It's about $60.
Also, the 20 mm is for 2" focusers only. The 9, 11, 12, 13, and 16 have a 1.25" barrel with a 2" skirt around the outside so you can use either size focuser. However, if you use a 1.25" on these "hybrids", your setup can look precarious. Use a 2" focuser if at all possible. Only the 4.8 mm and 7 mm have 1.25" barrels. The cost really shouldn't be a factor to you, if you plan to stick around in this hobby for any length of time. I view eyepieces as an investment. When I change scopes, my eyepieces stay with me. You're better off with one Nagler than a drawer full of Kellners. Besides, any semi-serious telescope owner who attends star parties will eventually see a Nagler (or a Panoptic, or a Pentax XL, or an LE, or a Lanthanum, etc) and that will be it. Most people who look through these eventually buy one.
The most serious optical drawback is "Kidney Bean" distortion. In the 9 mm, 11 mm, and 13 mm, there are these large, bean-shaped black areas that move around as you move your eye around. This annoys some people more than others, and is much worse in the daytime (in fact, TeleVue has started printing in their brochures that the 13 mm is "not suitable" for daytime viewing.) I describe my annoyance with the Kidney Bean distortion as moderate but worth putting up with. Above around 13 mm, the Kidney Bean effect becomes intrusive. As a result, TeleVue introduced its Nagler Type 2 series. These start at 12 mm and go up to 20 mm. Although the kidney beans are well-controlled, the eye relief got shorter. If you must wear glasses while observing, it is a MUST that you try out a Type 2 before buying one. The Type 2's control the "beans" by adding another element in the optical path, making a total of eight. This brings us to the final drawback. With so many lenses in the optical path, there is some loss of light throughput. This is most noticeable in smaller aperture instruments, where Naglers can look somewhat "dim". I have found this to be minor, but there are occasions when I have had to switch back to a Plossl or Orthoscopic, only to be surprised at the brightness of the simpler eyepieces. Again, this is a drawback I gladly live with. OK so far? On to the individual reviews...
(Type 1, $205 list, $170-$190 street)
A sharp-to-the-edge eyepiece with one small problem. The eye relief is so short that you have to practically place your eye on the lens to appreciate its wide field of view. Relief is rated at 7 mm, but I've found that you'll need to subtract 4-5 mm from this figure in actual use. The eye lens is also on the small side (only about 9 mm or so in diameter.) If you can accept the short eye relief, the 4.8 is a fantastic, sharp eyepiece for splitting double stars or resolving planetary detail. The 4.8 mm and the 7 mm are about the same size, but the 4.8 is about 15 mm shorter, and a little lighter. The 4.8 mm was once considered the ultimate high power eyepiece. While it is still a world-class eyepiece, there is now some significant competition. Vixen's Lanthanums (4 mm or 5 mm) have 20 mm of eye relief, as does the Pentax 5.2 mm SMC-XL. Some feel the Pentax is sharper as well (it should be, at almost twice the cost!) Finally, the new 3 mm, 4 mm, and 5 mm Radians are so comfortable, they are threatening make this eyepiece obsolete. In short, while not mandatory, the 4.8 mm Nagler is a nice luxury to have in your eyepiece case.
(Type 1, $255 list, $209-$229 street)
I find this to be an essential eyepiece. Even those who favor the equally fine Pentax XL 7 mm usually agree that the decision is close. If you must have maximum light output in a premium eyepiece, the Pentax may be for you; otherwise, the Nagler wins in all other categories: contrast, sharpness, FOV, etc. On a good scope, the views of Saturn can be stunning. Like the other Type 1s, there have been a number of revisions to this eyepiece. The most important one came a few years ago. TeleVue added a rubber grip ring, a recessed groove in the barrel for set screws, and a hard rubber eyecup. Older versions have smooth barrels with no rubber parts at all and have this "art deco" look to them. In addition, the color of the coatings has changed. Older versions have bluish-violet coatings, while newer versions have green coatings. The eye lens seems to have gotten smaller as well. My friends' older 7 mm seems to give more of the "space walk feeling". I think this is the only case where I prefer the older version. As with the 4.8 mm Nagler, this eyepiece is under significant fire from the new 6 mm and 8 mm Radians, which are much more comfortable and perhaps even a little sharper.
(Type 1, $305 list, $230-$260 street)
Another essential eyepiece, the 9 mm is probably the most used eyepiece in my case. Funny thing is, is doesn't seem to matter what scope I'm using, the 9 mm seems to feel "just right" in almost any situation. Slightly taller and about twice the girth of the 7 mm, it has a 1.25"/2" barrel. If you put your eye close to the front lens, and move your eye around, you can see the whole FOV, although moderately-sized kidney beans do follow you around. Still, it's not as objectionable as in the 13 mm. This is an extremely comfortable eyepiece to use. I can relax and look through it for a long time without getting tired. Also, it is not quite heavy enough to cause balance problems in most scopes. Like the other Type 1s, there have been many revisions. I think I like the newest version the best, with the first lens flush against the top of the eyepiece. Using the older "smooth" version, I kept worrying about dropping it, a terrifying proposition (if you do damage any of these eyepieces, TeleVue will repair them. Be sure and call them to get a return# before sending it back.) This eyepiece now has some significant competition from the 10 mm Radian, which is smaller, lighter, less expensive, and (some say) sharper (Al Nagler disputes this, saying the Naglers are all diffraction limited and are just as sharp as the Radians.) Try both before buying if possible to see which is best for you.
(Type 1, $395 list, $289-$329 street)
Wow -- what an eyepiece! The Nagler 13 is huge, and you will need to think twice before putting it in a 1.25" focuser (and don't forget to double- check all those set screws on your visual back, diagonal, focuser, etc!) The Nagler 13 looks like it could swallow a six-pack of 25 mm Kellners whole and still have room for dessert. You WILL have balance problems unless you re-balance your scope before using this eyepiece. This can be a bit of a pain if, for example, you want to go back to a 6-7mm eyepiece for high power viewing in the middle of your session (TeleVue now makes an "equalizer" weight assembly for your light eyepieces that makes them as heavy as the "big guns". Consider getting one, $60). Is all this worth it? Are you kidding? The views through this eyepiece are simply stunning. On a Ranger, the double cluster in Perseus is a breathtaking sight. I find I can go through a whole observing session with just this one eyepiece (and it's a good thing, too - I hate to rebalance). The sensation of "falling" into this eyepiece is quite palpable, and addicting. The 13 mm was the first Nagler I acquired. The first night I had it, I felt like a kid on Christmas morning who's just gotten everything he's wanted. The combination of the 13 mm Nagler and my 4" Takahashi is truly stunning. I have not tried the earlier versions. I should also note that the Kidney Bean Effect is at its strongest in this eyepiece. This may annoy you more than it does me, so try one out if you can before buying. This eyepiece was discontinued sometime in 1999. 12 mm Type 4 has been cited as its replacement. The last time TeleVue discontinued a Nagler eyepiece (the 11 mm, see below) it became a cult item, with prices on the secondary market to match. This, coupled with the 13 mm's general excellence, suggests that it may be wise to acquire one (or more than one!) quickly.
(Type 2, $375 list, about $300 street)
The first of the Type 2 Naglers, the 12 mm continues the tradition of optical excellence in the Nagler line. The Type 2 eyepieces contain 8 elements instead of 7, and do not suffer from the Kidney Bean Effect. However, some of the eye relief went away (check one out beforehand if you wear glasses while observing) and some observers feel (myself included) that the Type 2 Naglers are somewhat less sharp than their Type 1 counterparts. The compromise in design arose out of necessity. The 13 mm Nagler is about the largest eyepiece one can build. To achieve longer focal lengths, the eyepieces would have to be huge. According to Rutten and van Venrooij, a 25 mm Nagler would measure 5 inches in diameter and weight close to 25 pounds! Hence, the re-design, and a few sacrifices, with the Type 2 Naglers. Like the 13 mm, the 12 mm has a 1.25" barrel, with a 2" skirt around the outside. The 12 mm Nagler Type 2 has been discontinued in favor of the 12 mm Type 4.
(Type 2, $415 list, about $320-$340 street)
A most useful eyepiece, in a focal length that commands a lot of competition, some of it from TeleVue itself. The 15 mm and 19 mm Panoptics offer nearly as much FOV, for about 20%-30% less money. Still, the 16 mm is a whale of an eyepiece - comparing one to a conventional 15 mm Kellner or Plossl is a humbling experience (for the Kellner or Plossl, that is...) Strangely, the 16 mm is slightly smaller and lighter than the 12 mm. Also, those who wear glasses should be aware that it is rated for slightly less eye relief as well (10 mm, vs 11 mm.) 10 mm is getting "down there" in terms of relief. I'm beginnning to sound like a broken record, but try before you buy. The 16 mm is the last of the hybrid 1.25"/2" eyepieces.
(Type 2, $535 list, about $425-$450 street)
Awesome eyepiece. The 20 mm Nagler is the flagship of the TeleVue line (no longer! -Ed, 10/3/10), and its most expensive eyepiece by a healthy margin (until the Type 4 and Type 5 eyepieces came out in 1999.) Performance is simply incredible, and you should consider upgrading your visual back, diagonal, and focuser to 2" capability just so you can use one! Again, there is serious competition from TeleVue itself. The 20 mm Nagler's true FOV sits between the 22 mm and 27 mm Panoptics, which are great eye- pieces in their own right. Perhaps this accounts for the fact that I don't see many 20 mm Naglers out there (the Panoptics are slightly cheaper.) Eye relief is still smallish, at 12 mm. Still, the 20 mm Nagler is a great optical achievement, and offers jaw-dropping views. Looking through its huge, picture-window lens, it seems to take the telescope "out of the way," enough to make its lucky owner forget all about equipment, telescopes, and eyepieces for a while. That's the highest compliment I can give. This eyepiece was discontinued sometime in 1999. It's been replaced by the 22 mm Nagler Type 4.
(Type 1, NLA, about $300-$350 street)
The 11 mm is no longer made. It was a Type 1 Nagler, which never got to the "rubber" upgrades. According to "Ask Al Nagler", a decision was made not to re-tool for the 11 mm when the 12 mm Type 2 came out. If you think about it, if they had kept the 11 mm, there would be 11, 12, and 13 mm eyepieces (but now it looks as though only the 12 mm will survive.) On the other hand, anyone who's seen all of them can attest that each eye- piece has a totally different "character"; there's a lot more than 1 mm difference between them. The 12 mm, for example, feels nothing at all like the 13 mm. As a result, the 11 mm has become something of a collector's item and has gained a certain mystique about it. The ones I've looked through are simply wonderful; I'm not sure there is anything "extra" special about these eyepieces, other than their relative scarcity on the used market.
Update, 10/99: Back when I was a kid, my friends and I used to collect baseball cards. The frustrating part of this hobby was, as soon as you got close to collecting the whole series, they would come out with next year's cards. TeleVue's premium eyepieces are getting a lot like that. Just when you think you have a shot at getting them all, they come out with another must-have unit. In the Spring of 1999, TeleVue announced their new "Type 4" eyepices in 12 mm, 17 mm, and 22 mm focal lengths. The Type 4s are very expensive, so you should try before you buy if possible. At this time, the Type 1 models appear on their way out (collectors, take note!)
(Type 4, about $375 street)
These new Type 4 Naglers are relatively compact (about the size of the 27 mm Panoptic) but rather heavy. The 17 mm weighs in at 1.6 lbs, so be careful with your focus lock knobs. There is a click-stop eyeguard, and the unit is for 2" focusers only. Also, please be cautioned as there is a huge, honking piece of convex glass right at the bottom of the eyepiece that almost extends to the bottom of the barrel. You need to be very careful not to set the eye- piece down on the ground, as any stray pebble will scratch this lens. It's also a good idea to keep your fingers away from the bottom of the eyepiece. I used the 17 mm Nagler during a couple of clear February nights here in New Hampshire. It spent time in a Traveler, a 10" EL Starmaster, and the 20" Obsession. The views were stunning, just like the 22 mm, only with slightly more magnification. Very minor kindey beaning was noted, and this only happened when I placed my eye well off-axis. This eyepiece turned out to be the perfect companion to the 27 mm Panoptic in the Obsession. I spent an entire night with just these two eyepieces and never wanted for anything else. The 17 mm is also very fine for low power sweeping in the Traveler. The 17 mm Type 4 is somewhat more pleasing than the 16 mm Type 2 Nagler. It has a much bigger eye lens, and you don't have to strain quite so much to enjoy the image. Those of you looking to save some weight and size by buying the 17 mm as opposed to the 22 mm can forget about it -- the 17 mm is a tad larger and a couple of ounces heavier than the 22 mm, go figure. It is about $75 cheaper though. Highly recommended if you have the money and need a premium eye- piece in this focal length.
(Type 4, about $450 street)
This eyepiece comes in at a very competitive focal range. The 20 mm Type 2 Nagler is right behind it, as are the 19 mm and 22 mm Panoptics. However, this 22 mm Type 4 is a great, great eyepiece. It has a wider field of view than the Panoptics, and is smaller and lighter than the 20 mm Nagler. It is almost the same size as the 22 mm Panoptic, and were it not for the Nagler's heavy weight, you'd mistake it for the Panoptic at first glance. I used this eyepiece a number of times in the 20" Obsession and the 10" EL Starmaster. As with any good eyepiece, it simply "gets out of the way" and allows me to concentrate on the views. Very minor kidney-beaning was noted. The 22 mm is also less susceptible to false color at the field stop than some of the other Naglers (the Type 1s sometimes have this problem.) There's a click-stop eyeguard like the ones on the Radians. Compared to the 22 mm Panoptic (one of my favorite eyepieces, of any design), the views are just as sharp and contrasty, but the Nagler has a wider FOV and less pin-cushion distortion. The eyepiece is a 2" barrel only. Very impressive. It's expensive, though. Try before you buy.
(Type 5, $795 list, about $600 street)
It's amazing how quickly TeleVue has managed to raise the bar on premium eyepieces. Just as I was gawking over the $450 price tag of the 22 mm Nagler Type 4, along comes this bomb of an eyepiece. In one fell swoop, TeleVue has somehow made the 22 mm Nagler look almost like a bargain. The $350 35 mm Panoptic seems almost cheap in comparison. This is the largest eyepiece TeleVue has ever made by a wide margin. It's about the same height as the 20 mm Nagler and the 35 mm Panoptic, but much fatter. It weighs 2.2 lbs, and I don't feel comfortable holding it unless I use both hands. The first time someone handed it to me, I simply stared at it in my hand, dumbfounded. Three of us spent the evening swapping this into the 20" Obsession and the 10" Starmaster. Yikes -- what an eyepiece. It became apparent to us that this unit is probably going to replace the 35 mm Panoptic as the default low power eyepiece for large Dob owners. While the Pan- optic is superb, the 31 mm Nagler has a slightly wider true FOV and almost no pin-cushion distortion. Two of us independently thought that the Nagler had better contrast than the 35 mm Panoptic, more so than can seemingly be accounted for given the 10% difference in magnification. This eyepiece is heavy enough to cause some balance problems. Tip: if you buy one of these, you need to stay very close to your telescope during the first few nights. Unattended scopes, especially smaller ones, tend to slowly tip over, even when "balanced," with this eyepiece in the focuser. The sharpness was superb, and even stars out at the field stop were pinpoints. Very, very minor kidney-beaning was noted. Also, there is a minor ring of false color right at the field stop. There is no click- stop eyeguard. Finally, if it isn't already obvious, the barrel is a 2" only. Seeing the Veil in the 20" with an O-III filter was a sight that I'll not soon forget. Ditto for the Dumbbell, M71/Harvard 20, NGC7789, and the field around NGC6910 in Cygnus. This is an expensive piece of equipment, and a purchasing decision not to be taken lightly. For $600, you could set yourself up with a nice telescope. However, it is my painful duty to inform you that the 31 mm Nagler is worth every penny of its asking price. Your move.
End Nagler Overview