The 20mm Nagler Type 5 is a surprisingly compact 2” eyepiece that is a worthy successor to the heaviest commercial eyepiece ever produced. The original Nagler 20mm Type 2 weighed in at 37 ounces when it was introduced in 1986, and instantly became a favorite with owners of big Dobsonians due to its wide field, despite its weight. The new version weighs in at a svelte 19 ounces, about half the weight of the original. Despite the lighter weight, the 20mm Nagler Type 5 has all the optical virtues of the original.
The six-lens design uses multiple rare earth glass elements to give you a sensationally wide 82° field of view. It makes observing feel like you’re looking through a “picture window on space” rather than through an eyepiece. The 20mm Nagler is primarily designed for no-holds-barred low to 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. A soft fold-down rubber eyecup allows use with eyeglasses.
Please note the weight of this eyepiece if you have a Dobsonian telescope. Even in its new lighter incarnation, it is still a substantial eyepiece. Its use may require some temporary rebalancing of your scope, or the use of a TeleVue #TVEQC equalizing adapter with lighter 1.25” eyepieces to avoid balance problems.
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