The best observation is achieved by combining an excellent optical tube, with performance close to the diffraction limit, with an excellent eyepiece. This combination optimises the resolution of the instrument over the entire field of view. The Takahashi TOE eyepieces were designed with this objective in mind. Whether on Takahashi telescopes or on those of other prestigious brands, they allow the objectives of the various optical tubes to express their full potential, particularly in terms of resolution. They thus demonstrate that telescopes such as the TOA, TSA, FOA and FSQ, or telescopes such as the Mewlon-CRS are not only photographic instruments but also formidable tools for visual observation.

Takahashi TOE eyepieces have been designed for high magnification observation of the Moon and the planets with optimal comfort. On the TOA-130 telescope, 4 mm, 3.3 mm and 2.5 mm eyepieces are used to achieve magnifications of 250x, 300x and 400x respectively. On the FSQ refractor at F/5, it is strongly recommended to use an extender to change to F/8 in combination with TOE. The apparent field of view of the TOE is 52°, wider than the 40° of the old Hi-LE eyepiece, and the eye relief is identical to that of other Takahashi eyepieces such as the LE-5 or LE-7.5, making planetary observation particularly comfortable.

Optical aberrations in eyepieces are difficult to assess theoretically. Therefore, at Takahashi, the optical characteristics of the eyepieces are calculated, and the aberrations minimised, on the assumption that the eyepiece is a complete optical system mounted in afocal at the focus of the TOA-130 refractor. From an undulatory point of view, the Strehl ratio does not fall below 98%, whatever the wavelength considered (from 486 nm to 656 nm) and over the whole field. From a geometric point of view, the spot-diagram shows that the resolution is clearly below the Dawes limit calculated for the TOA-130 lens. Finally, it should be noted that the residual chromatic aberration is extremely low.

The optical design of the TOE eyepieces consists of 6 lenses divided into 4 groups. The Smyth lens of the first group and the main lens of the last group have been optimised to minimise spherical aberration, chromatic aberration, field curvature and astigmatism. Ghost images and reflections have been reduced, allowing the Moon and planets to be observed with high contrast. Each optical surface is treated with a full multi-layer, broad-spectrum treatment and an alternative treatment is applied to surfaces where the colour balance needs to be corrected and the contrast improved. Finally, all lens edges and internal metal surfaces are blackened to prevent stray rays.