2mm to 4mm Nagler 1.25" zoom eyepiece

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In conventional zooms, the apparent field of view and the usable eye relief change as the focal length changes. Likewise, because conventional zooms are not parfocal (they don’t focus at the same point at all focal lengths), objects go out of focus as the magnification is changed with an ordinary zoom. These anomalies don’t happen with this very high power Nagler zoom. It physically lengthens and contracts as the focal length is changed, as can be seen in the feature images you can click on above.

This unique approach (conventional zooms all move lenses within their body to change their focal length, while the Nagler physically changes its length) allows the apparent field, eye relief, and focus to stay the same, no matter what the focal length. You don’t have to constantly adjust the focus as you change powers, as you do with other zooms (minor tweaking may be necessary, however). And you don’t have to adjust your eye position to accommodate a changing eye relief and a changing field stop diameter.

This high-power Nagler zoom has five fully-multicoated elements in three groups, similar to a fine camera lens. By keeping the number of optical elements low, the contrast stays high when compared to other zooms with an additional two or three light-scattering lenses in their light path. The eyepiece has click stops at 2mm, 2.5mm, 3mm, 3.5mm, and 4mm for quick changes to precise preset magnifications. Naturally, you can use any intermediate focal length between the click-stops, as well. There's a fold-down rubber eyeguard and a rubber grip ring.

The Nagler zoom is designed to provide the best balance of contrast, comfortable eye relief, and resolution for the critical planetary observer, particularly those with ultra-premium short focal length refractors under 800mm in focal length, like the TV-60. It allows the observer to dial in the right balance between magnification, exit pupil, and atmospheric turbulence to achieve the best possible image for the observing conditions at any given moment. This is the ultimate tool for tweaking out the last bit of observing power that the atmosphere will permit.

If you own an ultra-premium short focal length refractor, or any other top quality short focal length scope, there’s no longer a reason to have to accept second best when it comes to high power lunar and planetary observing. This high-power Nagler zoom will match the quality of your scope optics. It will put to rest forever the idea that it is impossible to produce a zoom eyepiece that does not degrade the image.

Field of view:
The field of view (FOV) is the amount of observable world one can see at any given moment.
Eye Relief:
Eye relief is the distance from the last surface of the eye lens of an eyepiece to the plane behind the eyepiece where all the light rays of the exit pupil come to a focus and the circular image is formed, sometimes called the “Ramsden Disk.” This is where your eye should be positioned to see the full field of view of the eyepiece. If you must wear glasses because of astigmatism, you’ll usually need at least 15mm of eye relief or longer if you want to see the full field of view with your glasses on.

A note on our eye relief figures: Quite often, our eye relief figures will differ from those of the manufacturer. This is because we measure the “usable” eye relief, while the manufacturers specify their usually-longer (but technically correct) “designed” eye relief.

The eye lens of the eyepiece is normally recessed below the rubber eyeguard or rubber rim of the eyepiece to keep the lens from being scratched during use. An eyepiece might have a “designed” eye relief of 15mm (and the eye relief will truly measure 15mm from the eye lens to where the image forms). However, if the eye lens is recessed 3mm below the eye guard, the Ramsden Disk forms only 12mm above the eyepiece body (the 15mm “designed” eye relief, less the 3mm of eye relief made unusable by having the eye lens recessed into the body of the eyepiece). This “usable” eye relief of 12mm (measured from the rolled-down eyeguard – the closest point you can get your eye to the eye lens – to where the image forms) is the eye relief figure we would measure and list in this website.

Why is it important to list the “usable” eye relief? For those people who don’t wear eyeglasses while observing, a few mm difference between the eye relief they expect from the manufacturer’s literature and the shorter eye relief they actually get in real life doesn’t mean a lot. They can simply move a little closer to the eyepiece to see the full field, and never realize that the eye relief is a little shorter than they expected. However, some people must wear eyeglasses while observing, because of severe astigmatism. These observers can’t move closer to the eyepiece if the eye relief is shorter than expected because their glasses get in the way. For these people, the real life “usable” eye relief is more important than the technically correct but sometimes not fully usable “designed” eye relief. We measure and list the actual usable eye relief so that people in the real world can pick the eyepieces that will work best for them.

Focal Length:
This is the length of the effective optical path of a telescopeor eyepiece (the distance from the main mirror or lens where the lightis gathered to the point where the prime focus image is formed). Focallength is typically expressed in millimeters.

The longer the focallength, the higher the magnification and the narrower the field of viewwith any given eyepiece. The shorter the focal length, the lower themagnification and the wider the field of view with the same eyepiece.

Number of optical elements:
Barrel Size:
The industry standard diameter, as of 2011, is 1.25" and is the most common.  Other sizes available are .965" and 2".
The weight of this product.
5.7 oz.
Limited Lifetime
Reviews from Cloudy Nights (www.cloudynights.com)
These reviews have been written by astronomers just like you and posted on the Cloudy Nights astronomy forums . . .
TeleVue 3mm-6mm Nagler Zoom

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TeleVue - 2mm to 4mm Nagler 1.25" zoom eyepiece

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TeleVue - 2mm to 4mm Nagler 1.25" zoom eyepieceImage showing how the zoom’s eyelens extends and contracts as the magnification is changed.
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Our Product #: TNZ2
Manufacturer Product #: ENZ-0204
Price: $409.01  FREE ground shipping - Click for more info
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MSRP: $530.00

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Unlike conventional zoom eyepieces, this very high power Nagler zoom will not degrade the quality of the image you see through your premium short focal length telescope . . .

. . . our 36th year