Star diagonals are essential accessories for refractors and Maksutov and Schmidt-Cassegrain systems as they allow the light path to be directed at a more convenient angle, improving ease of use especially when viewing objects towards the zenith.
Although many models are push-fit into the draw tube of the respective telescope, this can allow some slippage if the diagonal is not securely tightened in place.
This is where the Celestron 2-inch mirror diagonal for Schmidt Cassegrains comes into its own.
Designed for primarily Celestron Schmidt-Cassegrain/Edge HD telescopes, the diagonal threads securely to the rear cell giving a solid connection with no slippage.
This keeps the optical path accurately aligned too and is ideal for both visual and imaging purposes.
Included is a 2-inch to 1.25-inch adapter and a sturdy aluminium case for protection when it’s not in use.
Being a 2-inch fit diagonal, the best views are with such eyepieces and we used the diagonal on the Astro Fi 6-inch Schmidt-Cassegrain with a range of 2-inch eyepieces including an Ethos 21mm.
Swapping between standard 1.25-inch fit diagonal and eyepieces and the 2-inch SCT diagonal two things immediately struck us.
The field of view, regardless of 2-inch fit eyepiece used, appeared slightly larger so we had more sky to play with. The views were also noticeably brighter.
The latter is down to the diagonal having its mirror coated with the same XLT coatings found on Celestron’s SCTs and we are sure this had an impact on our views.
Although the exit cone of light from the Astro Fi 6 is designed for a standard 1.25-inch fit diagonal we were nicely surprised at how the 2-inch diagonal improved it and can still recommend it as an upgrade.
This is a really nice quality star diagonal that would be worth adding to your accessory collection if you have a Celestron SCT.
Type 90° diagonal
Suitable for Celestron Schmidt-Cassegrain/Edge HD telescopes.
Supplier Celestron UK / David Hinds Ltd