After rigorous analysis and testing of various types of eyepieces using premium telescopes, the engineers at Takahashi have determined that the Plossl design is the best.
The TPL series uses highly refractive, low-dispersion glass and has an optical design that allows for outstanding image quality, with chromatic aberration at the center about half that of the Abbe series and about two-thirds that of the LE series eyepieces.
The image quality is extremely sharp from the center of the field of view to about half of the field of view. Although the star image quality degrades out toward the periphery, it is of high quality for visual observation, allowing the observer to focus on the center of the field of view.
The entire lens surface is coated with a multilayer coating that transmits more than 99% across the entire visible light range and has a high-quality matte finish, which prevents stray light from entering the lens.
The eye relief is approximately 70% of the focal length, and the apparent field of view is 48°.