1.25" star diagonal with 99% reflection, dielectric coating, L/10 PtV
The Castell star diagonal has dielectric coating, providing 99% reflectivity with much longer lifetime than normal or enhanced coatings. The mirror surface has only L/10 ptv error, which is really smooth, resulting in excellent image quality. The brass compression ring protects the eyepieces.
The advantages in a nutshell
For all 1.25" focusers
You can use this mirror star diagonal on any refractor, Maksutov or SC telescope which has a 1.25" focuser. The Castell star diagonal deflects the image 90° upwards to provide you with a comfortable viewing angle.
For all 1.25" eyepieces
Whether Ploessl or wide angle - this mirror star diagonal can take any 1.25" eyepiece. Compression spring ring clamping holds the eyepiece barrel in an optimal grip for any observing orientation.
Brighter images - mirror with 99% reflection
You can look forward to a bright and sharp image, with inconspicuous details or faint nebulae now seen even better. The reason - a mirror with multiple microscopically-thin deposited dielectric mirror layers achieving 99% reflection. That means - some 10 percent more light than the mirror diagonals that typically come as accessories with most telescopes.