| The 27mm Astro-Tech Flat Field is a very good low to medium power eyepiece for viewing emission and reflection nebulas and open star clusters, for scanning the star clouds of the Milky Way, etc. Its optical design provides a very flat field that keeps your image sharply in focus from one edge of its 53° field to the other. This flat field makes it a great match to the new breed of flat field/coma-free catadioptric telescopes.
The 27mm Astro-Tech’s flat field shows you views of open clusters in which all the stars in the cluster are in focus, not just those in the center of the field. The moons of the gas giant planets show as sharply focused dots when they are at their maximum extension on either side of their sharply focused parent planet, not as the out-of-focus smudges often seen in lesser eyepieces.
Its 27mm focal length gives an f/4.5 Dobsonian owner a wide and bright 6mm exit pupil (about the maximum to which most observers’ eyes can dilate) for engrossing rich field scanning of the Milky Way star clouds in Sagittarius. The clouds show myriad pin-point stars all across its wide 53° apparent field (a 1.25° actual field with a 10" f/4.5 Dob, two and a half lunar diameters across). And the 27mm Astro-Tech is an excellent choice to complement the 40mm eyepiece provided with some go-to Schmidt-Cassegrains.
This 27mm Astro-Tech Flat Field has an excellent 18mm eye relief for unvignetted images when used with eyeglasses. Best of all the 27mm Astro-Tech Flat field eyepiece is priced well below similar design eyepieces from other suppliers, and with double the warranty.
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