***** **********Best Quality Guranteed. *****85mm focal length, reduction factor of about 0.5X, depending on spacing. 0.5 x focal reducer effectively halves the focal length of a telescope, enabling lower magnification, a wider field of view, and shorter exposure times for astrophotography. *****2 lenses for better correction - cemented together and coated, black-anodized aluminum housing. *****Mounting threads - 1.25" filter thread ( 28.5 x 0.75MM ) on both sides: Threads into eyepieces, camera adapters, and other accessories with standard 1.25" threads, and can be stacked with additional 1.25" threaded accessories. *****Free light transmission - 22.5 mm lens aperture. Can be used with additional spacers (available separately) to achieve further focal reduction. *****Intended for use with with longer-focal-ratio telescopes and eyepieces of narrow to moderately-wide apparent fields of view.