Tele Vue Panoptic 27mm 68° Eyepiece - 2"

The 68° "Spacewalk" Experience for Any Telescope

Al Nagler's guide gives Panoptics a 68° apparent field, against 50° for Plössls and 82° for Naglers. The 27mm has 6 elements in 4 groups.

In a long focal length telescope such as a Schmidt-Cassegrain it works as a low-power finding eyepiece; in shorter telescopes it frames nebulae and clusters.

Field of View by the Numbers: The 30.5mm Field Stop

The true field, how much sky you see, depends on the field stop diameter and the telescope's focal length. With a 30.5mm field stop, the 27mm Panoptic provides a substantial swatch of the sky. Tele Vue's formula:

True Field of View = (Eyepiece Field Stop ÷ Telescope Focal Length) x 57.3

For example, in a telescope with a 2000mm focal length (like a typical 8" SCT), the 27mm Panoptic gives 74x and a 0.87° true field, more than the full Moon's width, with room around the Hercules Cluster (M13). The bright core of the Orion Nebula (M42) fits, but not its full extent.

Exit Pupils from f/4.5 to f/14: Performance Across Telescopes

The exit pupil sets how bright the background sky looks. Tele Vue's chart gives 6.0, 5.2, 3.9, 2.7 and 1.9mm at f/4.5, f/5.2, f/7, f/10 and f/14:

• f/4.5 Dobsonian: 6.0mm exit pupil, for nebulae under dark skies, and inside the 7mm limit for reflectors.
• f/7 Refractor: 3.9mm exit pupil, for open clusters and galaxies.
• f/10 SCT: 2.7mm exit pupil, a darker sky background for globular and planetary nebulae.
• f/14 Maksutov: 1.9mm exit pupil, still a low to medium power at these focal lengths.

Observing Comfort: 19mm of Eye Relief and Dioptrx Compatibility

With 19mm of eye relief, the 27mm Panoptic is comfortable for most observers, including many who wear eyeglasses. The suggested eye relief for observers who wear glasses to correct astigmatism is 15mm to 20mm.

The chart marks it Dioptrx ready (Y, no adapter). Dioptrx corrects astigmatism in place of glasses, is rotatable to the astigmatic axis and comes in ¼ to 3½ diopters. It is always completely aligned to the eyepiece optics, which eyeglasses are not.

For Fast Reflectors: Coma Correction with Paracorr Type-2

Newtonian and Dobsonian telescopes, especially those with fast focal ratios of f/5 or less, naturally exhibit an aberration called coma, which distorts stars at the edge of the field into comet-like shapes. Tele Vue's Paracorr Type-2 eliminates it, with the greatest results in scopes faster than f/5.0.

The Paracorr installs in your telescope's 2" focuser and acts as a 1.15x magnification extender, effectively turning an f/4.5 system into an f/5.2 system. The 27mm then acts like a 23.5mm. With Tele Vue eyepieces an object will be equally sharp anywhere in the field.

Higher Powers: Pairing with Tele Vue Barlows & Powermates

Tele Vue makes Barlows and Powermates in 2x, 2.5x, 3x, 4x and 5x. A 2x Barlow, for example, would transform the 27mm Panoptic into a high-performance 13.5mm eyepiece, for a closer look at globular clusters.

Panoptic 27mm vs. 35mm Panoptic and 31mm Nagler

Comparisons from Tele Vue's chart:

• vs. 35mm Panoptic: The 35mm Panoptic has a larger field stop (38.7mm), providing a wider true field of view at lower magnification. However, the 27mm Panoptic's smaller exit pupil (e.g., 2.7mm vs. 3.5mm in an f/10 scope) gives a darker sky background.
• vs. 31mm Nagler Type 5: The 31mm Nagler has an 82° apparent field and a 42.0mm field stop, so it shows more sky, and weighs 2.2 lbs against the Panoptic's 1.03 lb.

Build

The 27mm Panoptic weighs 16.4 oz (1.03 lb). Do not unscrew the chrome barrel! The lenses will fall out, voiding the warranty.

System Integration: Accepted Accessories for the 27mm Panoptic

Tele Vue's insert lists these for this eyepiece:

• Dioptrx Ready: Dioptrx fits without an adapter (Y in the chart).
• Bandmate Filters: Nebustar, O-III and H-Beta pass select wavelengths and darken the sky so nebulae "pop out".
• EBX-2120 Extender: Adds 1.2 inches to a 2" barrel, increases backfocus distance and can help parfocalize eyepiece sets.