| 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.
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