17mm 2" Nagler Type 4

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The TeleVue 2” 17mm Nagler Type 4 is a premium-quality eyepiece that further refines the "spacewalk" observing experience of the original Nagler and Nagler Type 2 eyepieces that have been the optical standard of the industry for years.

The 17mm Nagler has increased eye relief, higher contrast, and reduced pincushion compared to the original Naglers. This makes it exceptional for achieving a wide field of view at medium power with Dobsonian scopes.

The 17mm has TeleVue's unique "Instadjust" click-stop adjustable-height eyeguard, with a soft fold-down rubber eyecup. With the eyeguard retracted all the way, all of its generous eye relief is available for eyeglass use. The eyeguard can be raised in small and repeatable increments to position the eye of the non-eyeglass wearer the precise distance from the eyepiece to see the full field of view with maximum suppression of ambient stray light. A special doughnut-shaped removable plastic insert fits into the eyeguard to center the eye for those who have trouble positioning their eye precisely on a small exit pupil.

The 17mm is primarily designed for no-holds-barred medium power deep space use with scopes having focal ratios down to f/4. It is marvelous for open clusters, nebulas, and globular clusters with any scope, but is particularly effective with fast f/ratio reflectors. That being said, it must also be noted that its very wide field also makes it convenient for moderate power lunar and planetary observing with Dobsonians, as you have much longer to observe before the planet drifts out of the field and the scope has to be repositioned.

Please note the weight of this eyepiece if you have a Dobsonian telescope. Its use may require some temporary rebalancing of your scope, or the use of a TeleVue #TVEQC equalizing adapter with 1.25” eyepieces to avoid balance problems.

Field of view:
The field of view (FOV) is the amount of observable world one can see at any given moment.
82 °
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.

17mm
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.

17mm
Number of optical elements:
6
Barrel Size:
The industry standard diameter, as of 2011, is 1.25" and is the most common.  Other sizes available are .965" and 2".
2"
Weight:
The weight of this product.
26 oz
Warranty:
Limited Lifetime
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Overall Product Rating: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics(5.00)   # of Ratings: 2   (Only registered customers can rate)

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1. Jay on 5/23/2013, said: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics
The wide field is spectacular and seems sharp and impressive, my first look at Orion's sword with 6-inch f/5 floored me. I guess that's the "immersion" described for this eyepiece.

If you like the Radian instadjust feature (I do) you may find that 17 T4 takes a little getting used to: somehow, it's not just a bigger Radian for learning eye placement. View is great once you get it adjusted and get used to the larger diameter of the 17 T4.

Views thru short tube achromat and smaller f/5 reflector are stunning, a real treat for viewing larger-scale DSO. A paracorr cleans up coma in the reflector, the field is so wide you notice it in wide ring of outer field otherwise.

The size and 1.5 pound weight of this 17mm T4 (and the 27 Pan for another example) seem to be upper end of moderate weight that not's as bad for balance or feeling like a diagonal is overloaded, compared to the largest 40+mm 68 degree, 30+mm 82 degree or 20+mm 100 degree eyepices, some of which are 2-3 pounds.

I got the 17 T4 and 19 Pan at different deep sales about the same time, thinking they would be similar I would pick one to keep. Turns out I really like both, with 17 T4 a deep sky/dark sky favorite for the extra field of view in shorter focal length scopes, and the 19 preferred for moon, planets and deep sky details in f/10 scope.
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2. Robert on 3/3/2013, said: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics
Good, but not perfect. It suffers from field curvature requiring refocusing of the edges. It as has a tiny amount of astigmatism at the edge. These are both minor nits, but the center just does not snap into focus compared to the Pentax XL or XW lines or the Delos line. You are never quite sure if you have achieved best focus. It's almost as if there is astigmatism in the center. Off center seems slightly sharper. The immersion factor is great, no complaints at all there. 17mm of eye relief seems overstated. At that distance, you can see about 70 degrees at most. To get the true field stop, you must press in and then the exit pupil becomes difficult to hold. It's easier to just tilt your head to take in the edge. The eyeguard stayed put once set. Barlows quite well. A bit heavy at over 1 1/2 pounds. Very dense feeling in the hand. Recommended only if you must wear glasses and need an 82 degree field at this focal length. I would give it 9 out of 10 stars, but with only 5 stars max instead of 10, I'll give it the benefit of the doubt with 5 stars.
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Telescope Eyepiece Formula
To calculate the magnification and approximate actual field of view of this eyepiece on your telescope, enter the focal length of your telescope below and press the "Calculate" button.

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TeleVue - 17mm 2" Nagler Type 4

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TeleVue - 17mm 2" Nagler Type 4
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Our Product #: TN17
Manufacturer Product #: EN4-17.0
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The TeleVue 2” 17mm Nagler Type 4 is a premium-quality eyepiece that further refines the "spacewalk" observing experience of the original Nagler and Nagler Type 2 eyepieces that have been the optical standard of the industry for years . . .





. . . our 34th year