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TeleVue Nagler 3mm to 6mm Zoom eyepiece (ENZ 0306)
(update version -- including a comparison with the 5mm Nagler Type 6)

by Richard Orr, 28 August 2001. Reprinted with permission.

TeleVue Nagler 3mm to 6mm Zoom eyepiece. Right: TeleVue Nagler 3mm to 6mm Zoom eyepiece, provided by Company Seven, courtesy TeleVue Optics. (48,230 bytes)

The lure of a short focal length zoom is undeniable. Wouldn't it be great to have a single eyepiece that not only delivers the punch of high quality 6mm, 5mm, 4mm, and 3mm eyepieces but all focal lengths in between?

The magnification difference between short FL eyepieces, even at a millimeter spread, is substantial in most amateur scopes. Many times, when viewing the planets, I have had to retreat to a power lower than I really wanted because my next highest eyepieces jumped well beyond what the uncooperative atmosphere would allow. But with the zoom I could theoretically match the exact magnification with the atmospheric conditions.

I am very picky about my eyepieces and telescopes. I only have limited time to view the heavens and I want to make the most of it. Quality in optical equipment takes precedence even over aperture. On the other side, I am not rich, so I have to be careful and save for what I want. I am not going to buy a zoom eyepiece just because it reads TeleVue. But if a zoom eyepiece carries the Nagler name then it does peak my interest. Company-7 (a TeleVue dealer) in Laurel, Maryland was kind enough to let me take a preproduction (and later a production) model of the new Nagler-Zoom on a test drive and for the next few nights I put a few million light years on it.


I own four telescopes. My airline travel scope is a TeleVue 85mm F7 refractor on a Telepod head. My workhorse is a Astro-Physics 155mm EDF refractor on a Losmandy G-11 equatorial mount. Everyone needs a Dobsonian, mine is an 18 inch F4.5 Obsession. My first telescope of nearly 40 years ago -- which I can't bring myself to part with is a 60mm F15 Monolux achromatic refractor. The Dob and the older refractor can only take focal lengths of 6-3 mm on the best of nights, so I limited my test of the Zoom to the TeleVue 85 and the Astro-Physics Starfire.

The only eyepieces that I own in the focal lengths covered by the Nagler-Zoom are Radians. Therefore, these are the eyepieces that I compared the Zoom against. A couple of years ago I owned and used for planetary observation a set of Zeiss orthoscopics which included a 6mm and 4mm eyepieces. The clarity and contrast images of the Zeiss can not be surpassed and I thought I would keep these eyepieces forever. But then came the Radians. After testing the Radians against the Zeiss I sold the orthoscopics and invested the money on a complete set of Radians. The Radians were very close to the Zeiss in clarity, but were so much easier and more enjoyable to use because of the longer eye relief and wider field of view. I have never regretted making the upgrade. If you want (or need) to wear eyeglasses while observing, the Radians have no equals among eyepieces in the shorter focal lengths (below 12mm).


My currently owned Radians and Naglers look and feel like real eyepieces. In comparison, this little Zoom in the 3mm position looks like a 90 lb weakling with its neck stretched out. The Zoom has 10mm eye relief and a 50 degree field-of-view. The Radians have 20mm eye relief and a 60 degree field-of-view with clarity and sharpness that is legendary. The new 5mm Nagler type 6, has a 12mm eye relief and an 82 degree field-of-view with clarity and sharpness that for all intent and purposes is equal to the Radians. Radians and Naglers are at the apex of eyepiece evolution. I almost felt sorry for the little Zoom even before the testing began. My gut told me that it was going to get clobbered.

NAGLER-ZOOM MEETS THE TELEVUE 85 ( 30 - July - 2001)

The waxing gibbous moon, just shy of a 11 days old, dominated the sky with Mars just to the south and east. The TeleVue 85 was setup with the alt azimuth Telepod head on a sturdy tripod. Because of the wide field of view provided by the refractor a starbeam (1x) is all that is required to locate objects.

Clavius was in the moon's morning light and well placed to look for detail. I examined the large crater with the 6, 5, 4, 3 mm Radians (100x to 200x). Holding my breath I removed the final Radian and lowered the Zoom into the eyepiece holder. The whole field of the Zoom (6mm setting) was very clean and sharp against the moon with no distortion that I could see. Zooming up was a wonderful surprise -- what a kick. It was like you were flying closer to the crater. The image remained sharp throughout the zoom and no change in focus was needed. I immediately took off exploring the moon at 100x (6mm setting) finding an interesting crater and zooming in on it to 200x (3mm setting). After checking it out for a few seconds zooming back to look for something else. Absolutely cool.After wasting time joy riding around the moon I went back to Clavius to see if I could pick up differences in detail with the different zoom settings compared to the Radians. I could not.

Although the Zoom has an eye relief of only one half that of the Radian eyepieces, I found that the 10mm eye relief of the Zoom proved very comfortable to use. The Zoom's eye relief is a great improvement over most other 3mm to 6mm eyepieces on the market. Gone are the days of subjecting the eye lens on your short FL orthoscopics, or even Plossls, to those severe eyelash beatings. The 10mm eye relief of the Zoom is not enough if you need to use glasses; but if you are like me the astigmatism that forces me to wear eyeglasses when using long focal length eyepieces disappears (because of the small exit pupil) in the shorter focal lengths covered by the Zoom.

Before moving on to Mars, I star tested the Zoom. Perfect. In addition, I let the star move through the whole eyepiece field to see if distortions could be picked up near the edge. Excellent all the way around.

Mars is challenging in any scope. Eighty-five millimeters is just not enough aperture for Mars. To make matters worse a dust storm has washed out the southern hemisphere. Little could be made out except for the bright north pole hood and muggy dark markings beneath each pole. But I did gain additional appreciation for the zoom eyepiece. Since the TeleVue 85 is on an alt azimuth mount and I only use a red dot pointer, I often lose an object like Mars when switching heavy eyepieces (like Radians) at high power. This is especially common when I need to add or subtract a filter from one eyepiece and put it on the next one to be used. My only recourse when this happens is to return to a lower power eyepiece to place the object back into the center of the telescope. The Zoom makes life easy. If I lost Mars, I just zoomed down the power to the 6mm setting which gave me a one-half degree field, centered the object and zoomed up again. I used an orange W21 filter on the Zoom and thus had the filter present through the whole range of powers.

One more plus for the little Zoom. I often take my TeleVue 85 on airplanes when traveling and am always debating which eyepieces to take in the carrying bag. The most difficult choice is deciding what high power eyepieces I am going to take for the planets and double stars. With the Zoom you get the full range of high power eyepieces in a single eyepiece slot in the travel bag. This would provide me with plenty of space for those big 2 inch wide field eyepieces that I just can't live without. An advantage that is hard to pass up.


The waxing gibbous moon had grown a day older. Gassendi was in the moon's morning light and became my first test object. The Zoom provided a range of powers from 182x (at the 6mm setting) to 364x (at the 3mm setting) in the large refractor. I was taken back by how much wider the actual field-of-view was with the Radians than the Zoom. It was surprising how much a 10 degree apparent FOV difference in eyepieces can make.

When it came to clarity, lack of distortion, seeing detail and all else (except field of view) the Radians and the Zoom appeared equal. The Zoom is well corrected throughout its range of powers and, as with the smaller refractor, no change in focus was needed.

Mars had its desert face on tonight (CM = 128 @ 10pm EDT) so it lacked most of the dark markings that I could use for a good comparison. However, the Zoom did show one of its real strong points when looking at Mars and that is its ability to provide continuous power changes.

The 4mm Radian gives 273x and the 3mm gives 364x. That is almost a 100x difference! The atmosphere was holding the 4mm Radian but not the 3mm Radian. With the Zoom I was able to find the maximum power that Mars and the atmosphere would allow me to use. It was about - way between the 4mm and 3mm setting. Yes, I could have used a Barlow, lower power eyepieces and lots of experimenting and achieved the same end, but what a hassle. In addition, the atmosphere often changes over the course of a night and with the Zoom and a slight twist of the wrist you can match the magnification to the atmosphere. This type of micro-managing the atmosphere at maximum power is just not possible with normal eyepieces.

I star tested the Zoom throughout all range of powers and across the whole field of the eyepiece. If there was distortion it was below what I could detect. The Zoom is a really well corrected eyepiece. How is that done with a zoom? Looks like Al has once again set a higher bench mark for eyepieces.

The rest of the observing time was spent on a few deep sky objects. I was limited because of the bright moon but still had a great time. The double-double was cleanly split with the Zoom at the 6mm setting. This and a couple of other double star observations, convinced me once again, that for clarity and lack of distortion, the Zoom can hold its own against anything out there.

M13 was a real treat in the Zoom. While zooming you could actually see new stars appear as the resolution and the darkening of the background sky improved. I have known that higher power makes the background sky darker and that higher power will improve resolution within a globular cluster but I confess I have never felt it down in my bones like I did with the Zoom. What a ride!

After endless zooming in and out on M13, I took a minute away from the Starfire to watch the International Space Station pass over head. It really does not get much better than this.


Conclusion. This is one impressive little eyepiece. It is not a Radian or a Nagler, but it never claimed to be. The Zoom can take you on rides through the universe that no single or even combination of eyepieces can provide. The image quality provided by the Zoom is as good as your telescope. There really is no compromise in image quality by using the Zoom over traditional high power eyepieces (including high quality orthoscopics and plossls) or modern high-end complex eyepieces (including Radians and Naglers).

I wear eyeglasses but my astigmatism is non-existent at the focal lengths used by the Zoom. The advantage of size and ease-of-use with my travel scope, the micro-managing of atmospheric conditions at high power, and the incredible rides that zooming provides, makes it really tempting to add the Zoom permanently to my eyepiece case.

Now I just need to find out how much Company-7 asks for its demo (used) Nagler-Zoom eyepiece.



By the time I could get a hold of the new Nagler 5mm eyepiece the actual production run of the Nagler Zoom was out. I was asked by Company-7 to compare the new Nagler 5mm with the Radian 5mm, but I could not resist also comparing the Zoom (at the 5mm setting) against its big brothers.

Company-7 loaned me a Nagler 5mm eyepiece and one of the new and improved production run Nagler Zooms. In reality, the only difference that I could see between the commercial Nagler Zoom and the preproduction model (that I tested earlier) is that a new field stop was added to ensure that stay light does not produce a ghost when the eyepiece is placed next to a very bright object such as the moon. With the improved field-stop, I could follow the earthshine edge of the first quarter moon with the eyepiece without even a hint of light-ghosting from the sunlit side. This is something the preproduction model could not do.

The comparison of the new Nagler 5 versus the Radian 5 is provided in a separate review; as is my views on the Nagler 5mm itself. However, for the purposes of this review when it comes to clarity and sharpness the Zoom held its own against these two competing giants. Field-of-view and eye relief comparisons were made between the Zoom and the 5mm Nagler but they conform to what is advertised by TeleVue and thus need not be repeated for this review.

Richard Orr August 28, 2001


Contents Copyright 2001 Richard Orr, Used by Permission All Rights Reserved