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This proprietary zoom eyepiece is a spotting scope eyepiece with a 1.25” barrel that has found good acceptance as an astronomical eyepiece usable in any telescope accepting 1.25” eyepieces. It uses six lenses to achieve a wide field of view that varies, depending on the zoom setting. Its eye relief varies from 18mm to 12mm, depending on the zoom setting, and will give essentially unvignetted views at the lower powers for those who must wear eyeglasses while observing. Rotating the eyepiece’s rubber eyecup raises and lowers it to the desired height to customize the eye relief to match your eyesight. It is threaded for standard 1.25” light pollution and color filters. All lenses are fully multicoated with Pentax’s proprietary Super Multi-Coatings (SMC) and have blackened lens edges for better contrast. An ED (extra low dispersion glass) element minimizes chromatic aberrations and astigmatism. It is usable for all types of observing, with all telescope types, and is corrected for use with focal ratios down to f/4. It has good contrast and excellent center to edge sharpness, with very little ghosting. This is a quite good zoom eyepiece at a price that is quite reasonable for the performance you enjoy.