Choosing a Set of 1.25" Tele Vue Oculars
By Chuck Hawks
You've heard that Tele Vue eyepieces are the best (or close to it) and the guys in the astronomy club have let you look through some of theirs, so now you're ready to take the plunge. Before you reach for your wallet, there are some things to consider. Actually, there are many things to consider, since Tele Vue has one of the largest selections of eyepieces in the business. Lumping all Nagler Series oculars into one line still leaves five Tele Vue ocular lines, each built to different design parameters, and three zoom oculars.
One thing you won't have to worry about is uniform quality. All Tele Vue oculars and Barlows are fully multi-coated and use the best optical glass for the purpose. In many cases this is extra-low dispersion (ED) glass. They are individually (100%) quality controlled at the Tele Vue facility in Chester, New York. Even those destined to be sold in Japan are first shipped to New York for final inspection by one of Tele Vue's Far East suppliers and then shipped back to Japan. Tele Vue oculars are unique, built to Tele Vue's design and specifications. They are not re-labeled versions of generic Chinese oculars, although some other manufacturers (not Tele Vue's suppliers) have tried to copy Tele Vue designs.
For the purpose of this article, let's assume that you want to build a set of fixed focal length oculars with focal lengths from 7-8mm up to 40mm. In addition, you probably want a Barlow lens and a "catch all" zoom eyepiece. Some choices will clearly have to be made, based on your personal viewing preferences and, perhaps, the size of your bank account. Here is how I would go about building a set of Tele Vue eyepieces.
Long focal length oculars
Tele Vue Plossl oculars have established a reputation as the best Plossls on the market. Their 32mm and 40mm Plossl oculars deliver very sharp, flat field views with plenty of eye relief. The apparent field of view (AFOV) of the Tele Vue 32mm Plossl is 50-degrees and the eye relief is 22mm. The AFOV of the 40mm is 43-degrees and the eye relief is 28mm. In both cases, that is adequate eye relief even for eyeglass wearers.
Interestingly, because of their different AFOV's, the actual field of view of these two oculars is the same in any given telescope. The 40mm will be brighter, because of its larger exit pupil, while the 32mm makes everything in the field of view look larger. If money is tight, the beginner with a short to medium focal length telescope (up to about 1000mm) can probably get by, at least initially, with just the 32mm Plossl. The person with a longer focal length telescope in the same situation can probably make do with just the 40mm Plossl. Eventually, of course, it is nice to have both.
These are very good low magnification eyepieces. If you want to stay with 1.25" eyepieces, they are really the only choices, since they are the longest focal length oculars offered by Tele Vue.
24mm to 26mm oculars
Chances are that a 25mm Plossl eyepiece came with your telescope. It is probably a decent ocular and there is no overriding reason to replace it. However, it is not a Tele Vue, either (unless you purchased a Tele Vue telescope). If you want a Tele Vue eyepiece in this focal length range, the possible candidates are the 25mm Plossl or 24mm Panoptic. The Plossl has a 50-degree AFOV and 17mm eye relief. Like all Plossl oculars, its symmetrical optical formula calls for four-elements in two groups and it is very sharp and contrasty. It is also considerably less expensive than the 24mm Panoptic and has greater eye relief, so if your budget is tight, go with the Plossl and don't look back.
The Panoptic is designed with six-elements in four groups and has a 68-degree AFOV and 15mm eye relief. Either ocular will do a first rate job, but the Panoptic is designed to provide the widest field of view possible in a 1.25" eyepiece. Its 27mm field stop is the same as the 32mm Plossl, so I would opt for the Panoptic if I could afford its higher price, figuring that a 24-25mm ocular will be used primarily for deep sky and terrestrial viewing; in either application the wider field of view will be an asset.
In this focal length range, Tele Vue offers the 20mm Plossl, 19mm Panoptic and 18mm Radian. The Plossl is a four-element design with a 50-degree AFOV and 14mm eye relief. It is a good, sharp ocular and it is significantly less expensive than the Panoptic and Radian. It even edges-out the Panoptic in eye relief. If you are on a budget, the 20mm Plossl is the way to go.
However, the Plossl is outclassed by the six-element in four groups Panoptic and Radian designs in at least one area, since they offer 68-degree and 60-degree AFOV's respectively. They are not necessarily sharper, but they do take in more sky.
As mentioned in the section above, the Panoptic line is designed to maximize AFOV; its eye relief is 13mm, slightly less than the eye relief of the 20mm Plossl. Both the Plossl and Panoptic come with fold-down rubber eyecups. The Radian line, while offering generous 60-degree AFOV's, is designed for a consistent 20mm eye relief to accommodate eyeglass wearers and others who prefer not to squint through their telescope eyepieces.
Radian eyepieces incorporate click-stopped, pull up eyeshades. These help to eliminate ambient light while aiding in proper eye positioning for non-eyeglass wearers. Tele Vue's Instadjust is the best eyecup I have used to date. Also unique is the accessory Pupil Guide, a thin plastic disc that fits beneath the Radian ocular's rubber eyeguard and is supplied with all Radian oculars. Its purpose is to help novice observers zero-in and stay centered over the exit pupil.
I don't usually wear eyeglasses when viewing and if I had a sufficiently fat wallet, I'd like to experiment with that 68-degree AFOV offered by the Panoptic, but your selection may differ. All three of the Tele Vue oculars in this focal length range are top performers, so you cannot go wrong.
For the beginner on a tight budget who wants to get started observing with the minimum initial cash outlay, the 8-24mm Click-Stop Zoom offers interesting possibilities. It is sharp and has good eye relief, but a restricted AFOV in the 17-23mm focal length range. It is covered in more detail below.
Short focal length oculars
Tele Vue built their reputation on Al Nagler's original short focal length ocular designs. Since the introduction of the original Nagler oculars, Tele Vue and Al Nagler have continued to improve the breed and introduce newer designs. Today's 1.25" Nagler Series 6 oculars offer huge 82-degree AFOV's and 12mm of eye relief. The Radian line, also designed by Al Nagler, offers 60-degree AFOV's coupled with a generous 20mm eye relief. Compared to the short focal length designs of the past, primarily the orthoscopic and Plossl types, these Nagler designed oculars are a revelation and they sparked a revolution in telescope ocular design.
The Nagler 6 optical formula uses seven-elements in four groups. It is said to have increased contrast compared to earlier Naglers, while retaining the sharpness for which the design is famous. Nagler 6 oculars are also smaller and lighter than their predecessors. They are supplied with rubber fold-down eyecups. The Nagler 6 focal lengths are 2.5mm, 3.5mm, 5mm, 7mm, 9mm, 11mm and 13mm. Very few observers will need the two shortest focal lengths and most customers will not require a 5mm ocular, either, unless they are buying oculars for a short focal length telescope with a fast f/ratio. It is the 7mm, 9mm, 11mm and 13mm Naglers that primarily concern us here.
The ultra-wide 82-degree AFOV pioneered by Tele Vue with their Nagler line of oculars is beloved by many observers, but I am not among them. The AFOV is so wide that you must move your head around to see the edges, which I have always found annoying. However, it is very cool to have a short focal length Nagler or two and if you dote on an ultra-wide AFOV, then the Naglers are definitely for you.
I prefer to observe with the 60-degree AFOV and the longer 20mm eye relief of Al Nagler's Radian design. I don't usually wear eyeglasses while observing, but if you do, you will love the Radian oculars. Radians deliver full field sharpness with true orthoscopic linearity. This is achieved by the use of exotic glasses and clever design. Naturally, all of the short focal length Radians include the Instadjust pull-up eyecup and Pupil Guide accessory.
Radians are available in focal lengths of 18mm (already discussed), 14mm, 12mm, 10mm, 8mm, 6mm, 5mm and 3mm. For our purposes, unless you are using a short focal length telescope with a large objective, it is the 14mm through 6mm focal lengths that will be of greatest interest.
Tele Vue also offers traditional Plossl oculars in short focal lengths, including 15mm, 11mm and 8mm. Like all Tele Vue Plossls, these are sharp, contrasty, flat field oculars with a 50-degree AFOV (plenty for high magnification purposes). What the short Plossls lack is eye relief. The 15mm Plossl has a reasonable 10mm eye relief, but the 11mm Plossl is cramped at 8mm of eye relief and the 8mm Plossl has only 6mm of eye relief.
Having had quite a bit of experience with Plossl oculars, I suggest that the 15mm Plossl is fine if you don't need glasses when viewing. (If you must wear eyeglasses, you're going to need Radians.) The 11mm Plossl is marginal and the 8mm has such short eye relief that I find it uncomfortable to use.
I'd advise someone on a tight budget to consider starting with the 8-24mm Click-Stop Zoom (see below) instead of two or more fixed focal length oculars in the 2.5-23mm range. The zoom performs particularly well in the short focal lengths, it has comfortable eye relief and it is priced about like an 8mm Radian. Later, as finances permit, dedicated fixed focal length oculars can be acquired.
Although Tele Vue offers two very short focal length Nagler zoom oculars, only the 8-24mm Click-Stop Zoom fits our purpose as a multi-role eyepiece. This fully multi-coated, seven-element in four groups, 8-24mm zoom eyepiece is widely regarded as the best on the market. It has an AFOV of 40-55 degrees (40 degrees at 24mm and 55 degrees at 8mm) and offers 20-15mm of eye relief. The Click-Stop Zoom accepts Tele Vue DIOPTRX astigmatism correction lenses, so that eyeglass wearers can view without their glasses. These fit below the ocular's rubber eyecup ring. Tele Vue claims that this zoom "combines beautifully with our Barlow lenses."
After considerable research, I bought a Click-Stop zoom for myself and I would recommend it to anyone who wants a top quality zoom ocular. It is the sharpest zoom ocular I have ever used and the only one that I consider the equal of good fixed focal length eyepieces in resolution, contrast and color fidelity.
Zooms are handy for determining the correct eyepiece focal length that the subject and seeing conditions will allow. They are also useful when several people are using the same telescope and want to see the subject at various magnifications and/or fields of view. The 8-24mm Click-Stop Zoom is a useful addition to any ocular collection and it can be used as the medium-high to high magnification ocular in a beginner's basic three ocular "starter set."
2x Barlows double the focal length of your telescope, thus (in effect) doubling the magnification of whatever ocular you put in them. If you have a complete set of oculars you really don't need a Barlow lens and if you are just starting to build an ocular collection there are more important ways to spend your money. However, everyone seems to have a Barlow and, occasionally, they can come in handy. Tele Vue offers 2x and 3x Barlows with 1.25" mounting barrels.
These Tele Vue Barlows are fully multi-coated and use high index glasses in a two-element ED design. Tele Vue claims optimum aberration correction and exceptional contrast. Their literature states, "Observed performance is aberration free, even when tested with f/4 scopes." The Tele Vue Barlows use ring clamps to securely hold eyepieces without scratching. The 2x model should offer plenty of magnification boost for any reasonable purpose. Remember, get your other oculars first and the Barlow last.
1. Here is a full set of 1.25" Tele Vue oculars chosen without regard for price:
2. Here is a list of 1.25" Tele Vue oculars for those who want the best on a budget:
Copyright 2009, 2011 by Chuck Hawks. All rights reserved.