William Optics Dielectric Diagonal

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William Optics 2" Dielectric 90 deg. Diagonal

Price.. $199.95 + shipping




This 90 2” mirror star diagonal uses premium dielectric coatings for an exceptionally high 99% reflectivity. In addition to higher reflectivity than a conventional aluminum or silver coated diagonal, the dielectric coatings also provide higher contrast and resolution during critical planetary, lunar, and binary star observations. The precision first surface mirror uses a 10mm thick substrate for optical stability and is polished to 1/10th wave accuracy for sharp, high contrast images. A safety stop at the bottom of the 2” eyepiece holder tube prevents 2” eyepieces or 2” Barlows from hitting the surface of the mirror.

The diagonal comes with a 2” to 1.25” adapter to allow the use of 1.25” eyepieces. Both the 2” eyepiece barrel and the 1.25” adapter use soft non-marring copper clamp rings to hold eyepieces in place, rather than metal thumbscrews that can gouge the chrome barrels of your eyepieces. The clamp rings themselves are tightened by large knurled thumbscrews that are easy to operate, even when wearing gloves in cold weather. The 2” barrel that slips into the focuser or visual back and the 1.25" adapter are internally antireflection threaded for higher contrast. They are also threaded to accept standard 2” (48mm) filters. Grooves cut into the outside of the 2” barrel and the 1.25" adapter act as safety stops to keep the diagonal or adapter from falling should the scope’s visual back or eyepiece holder thumbscrews loosen slightly from cold or use.


The diagonal is designed for refractors with 2” focuser drawtubes and for those Meade LX200GPS models using the Meade electric Microfocuser. It will also work with other Schmidt-Cassegrains by adding optional rear cell adapter #7785C.


This is a premium 2” diagonal that is visibly superior in light transmission, optical quality, and workmanship to the economy and mid-priced 2” diagonals available from telescope manufacturers. It's a worthy upgrade for virtually any Schmidt-Cassegrain, Maksutov-Cassegrain, or refractor that can use a 2” star diagonal.

The William Diagonal is comparable to the Tel-Vue and others costing $75.00 to $100.00 more.

I give it 2 thumbs up. When viewing stars they where pin points from edge to edge, no distortion. Viewing the moon, very good contrast.

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