GSO's 90-deg mirror diagonal is a very good, economical replacement for the generic diagonal that probably came with your otherwise fine scope. Features Al+SiO2 coatings with 92% reflectivity across the visible spectrum and a 1/10 wave mirror.
The clear aperture is 27.9mm. The main mirror housing is made of precision molded ABS plastic and the two end barrels are precision machined from aluminum. The 1.25" nosepiece is threaded to accept standard 1.25" astronomy filters.
Not suitable for newtonian type telescopes. these are designed for refractors and some Schmidt-Cassegrain & Maksutov-Cassegrain telescopes