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13mm Nagler Type 6

The Type 6 Nagler is the most current version of an optic devised by Al Nagler in the 1980s. This design solves the triple equation of a wide field (82° AFOV), edge sharpness, and suitability in fast scopes. Early versions used a 2" barrel or a dual 1.25"/2" barrel, but the Type 6 has a 1.25" barrel exclusively. The eyepiece possesses seven elements, and some of the lenses are placed in the chrome barrel, but there is enough clearance for filters. Per TeleVue specifications, the field stop is 17.6mm. Eye relief is listed as 12mm, but I've found it to be somewhat tighter, on par with my 9mm University Optics ortho. Coatings are uniformly excellent.

TeleVue claims the Nagler provides a "spacewalk" experience. I've found that to be true. The FOV is immense. Often I feel as if I'm sticking my head into the eyepiece to take in the whole view. It extends to the edge of my periperal vision. Getting "up close" with the Nagler does require close eye placement, with occasional blackouts in the center of the FOV. Contrast, even at relatively low powers, is superb. In long focal-length scopes, the Nagler is a surprisingly good planetary eyepiece.

My observations were made at two sites in rural Iowa. Tranparency was above-average to outstanding. Seeing tended to be average or worse. The jet stream was parked overhead during much of this time, causing clear-air turbulence. For my low-power viewing, I used a Stellarvue AT 1010 refractor (80mm, f/6), yielding 37x and a 2.1° FOV. High-power viewing was via my club's 12.5" f/9 Ritchey-Chretien (219x, .36°), compared against a 13mm Gary Russell SWA ep (219x, .31°) and a Vixen LV Zoom set to 13mm (219x, FOV unknown but smaller).

Low-Power Observations: The Double Cluster was a natural target for the Nagler. The star-filled view was fabulous. The Nagler consistently revealed more stars and much better contrast than a 16mm Plössl (30x, 1.7°). It showed color differences in the stars and gave an excellent sense of the shape of each cluster, including the outlying members. On the moon, the Nagler provided a sharp view and much less false color than the plössl. Surprisingly, it also showed less false color than the 9mm University Optics ortho. Saturn was crisp and bright, with a slight purple glow. Barlowing the Nagler (Celestron Ultima barlow) reduced the color even more and gave a nicely-detailed view. The Cassini Division and one equatorial belt were easy to discern, along with five moons. The shadow of the planet on the rings was visible. Considering that this setup put ten elements in the light path, the brightness and sharpness of the image were impressive.

The 2° FOV comes into its own on the sword of Orion. Most people are aware that the central "star" of the sword isn't a star at all, but rather the great nebula M42, primarily illuminated by a group of young stars called the Trapezium. But did you know that the hilt of the sword isn't a star, either? It's the open cluster NGC 1981, with a visual magnitue of 4.6. Only the tip of the sword, Iota Orionis, is a true star, but in keeping with the overall theme it's a double featuring a mag. 2.8 primary and a pale blue mag. 6.9 companion. The Nagler offers up all of these treasure in one field. The cluster is a tight sprinkle of faint stars, M42 is a ghostly wisp enfolding the four major stars of the Trapezium, and Iota Orionis splits cleanly. Speaking of which, the Nagler splits doubles like a chisel, despite the low power. The four main stars of the Trapezium are sharp and bright, with clean dark spaces between them. Polaris is always easy, despite the 7-magnitude difference between its components, and Almach and Alberio are perfect in size, color, and separation.

A brief glimpse at M42 through my club's 10" f/6 Dob (115x, ,71°) confirmed the sharpness of the Nagler's optics. M43, which often fuses into the larger nebula, showed sharp edges and a wide, dark separation from M42. The detail in the Great Nebula was astounding. It appeared as a series of fine veils, overlaid so as to be now thicker, now thinner against the inky background. The definition of the filamentary edges was nearly photographic. This Dob does possess a Cave mirror, which probably contributed to the amazing image quality.

High-Power Observations: A fellow club member fortunately happened to have a 13mm Gary Russell SWA eyepiece, and he was willing to match it against the Nagler in the club's 12.5" f/9 Ritchey-Chretien. We were limited to sub-average seeing; the lower 40% of the sky was unsteady. Despite the conditions the Nagler showed a good split of Rigel, which was riding low in the muck. At 219x, the bluish companion stood cleanly free of the primary, which was a violently boiling ball of light. The Nagler offered better contrast on the split than a Vixen LV Zoom set to 12mm (238x), despite operating at a lower magnification.

Here are the results of the head-to-head comparison.

Saturn: On the gas giant, the Russell showed on-axis ghosting and a separate, prominent ghost of the secondary at 4:00 relative to planet. The Nagler produced a small, bright diffusion of light around the planet on-axis. The Russell showed 4 moons, with the two faintest requiring averted vision. The Nagler also showed 4 moons, but all were visible directly, and the background was darker. The shadow of planet on the rings was easier to discern in the Nagler. Both eyepieces showed one equatorial band. The Russell showed some brown color in band, but no color on the planet. In contrast, the Nagler revealed some pastel-like planetary color, shades of brown fading to yellow toward the poles. In fleeting moments of better seeing, the Nagler revealed fine banding on the planet. Both eyepieces revealed the Cassini Division (fleetingly early, more stable later as the seeing steadied). On a night of better seeing a couple of weeks later, the Nagler offered up fantastic views of the planet, revealing no fewer than 6 moons. Every prominent feature was easily visible: the polar hood, shading and structure in the equatorial belt, extensive banding, and colors ranging from mustard to ocher to taupe to tan. Some grooving was apparent in the A ring, fleeting glimpses of crepe ring were noted, and Cassini was so clear, wide, and sharp that you could dangle your feet over the edge.

M36: This smallest and most condensed of the open clusters in Auriga appeared quite different at high magnification. The cluster overwhelmed the FOV and appeared more as a stellar cloud. The Russell showed good structure in the cluster, with discrete groupings of stars. The Nagler also revealed these structure but cleanly showed about 30% more faint stars. It also betrayed its only optical flaw, some distortion at the edge of my peripheral vision which shifted as I moved my eye.

M79: Globular clusters are a natural target for high powers and large apertures. The worst image came from the LV Zoom, which gave a dim image and did not resolve any of the individual stars. The Russell, in a definite step up, showed the shape of the cluster, and with averted vision the core could be partially resolved. The Nagler revealed more stars at the edge of the cluster and gave a better sense of the overall shape. The core resolved easily with direct vision. In the Nagler, this object was obviously a swarm of stars, while in the Russell it was more of a smear with an occasional star.

Naglers aren't cheap; in fact, all the other eyepieces in my collection would just about add up to the cost of the 13mm Type 6. But the views are worth it. Until you reach the rarefied heights of optical performance (Astro-Physics triplets, my club's $13,000 Ritchey-Chretien), every other element of the light path will give out before the Nagler does. I originally envisioned it as a splurge eyepiece, but it has come to dominate my viewing time. Highly recommended.


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