This right-angle erect image finderscope is a sensible replacement for the straight-through inverted image 9 x 50mm finder supplied with many current Celestron telescopes. It allows you to comfortably use the finderscope without having to turn your head upside down to view near the zenith, as you do with the standard straight-through finder.
The right-angle first-surface mirror diagonal gives images that are upright, but mirror-image reversed, just as they are in the eyepiece of a refractor or catadioptric telescope. This makes the finder particularly useful with Celestron refractor and Schmidt-Cassegrain scopes, as the finder's image orientation matches the upright mirror-image orientation you see in the scope's eyepiece.
This fully multicoated achromatic doublet finder is also a good replacement for the straight-through finders supplied with older Celestron scopes. Its neutral black color also lets it be used to replace the straight-through and smaller finders that often come with other brands of telescopes.
Its large 50mm aperture has a limiting magnitude of 11, fainter than the stars on any commercial star chart, making it easy for you to locate faint nebulas and galaxies. The field of view is a generous 7 degrees wide and the eye relief is a very good 15mm. There's a rolldown rubber eyecup for eyeglass use. The finder weighs 17.6 ounces, without optional finder bracket. It will fit into the 50mm finder dovetail supplied with those Celestron scopes that come with a straight-through 9 x 50mm finder as standard equipment. If you're upgrading from a smaller finder, reflector-type dual mounting rings and an SCT-type quick release dovetail bracket are available as options. The 54.5mm diameter body of the finder is aluminum, painted in Celestron black, and internally baffled for higher contrast. The black anodized aluminum lens cell has an extra long integral shade to retard the formation of dew and shield the objective from ambient light. The lens shade has internal anti-reflection grooving for higher contrast.
The right-angle first surface mirror diagonal gives images that are upright, but mirror-image reversed, just as they are in the eyepiece of a refractor or catadioptric telescope.
The supplied crosshair eyepiece is removable and has a standard 1.25" barrel. It is held in place by a thumbscrew to allow easy orientation of the crosshairs to match the optical axis of the scope. You first rough-focus the finder by loosening the thumbscrew in the diagonal's eyepiece holder and sliding the eyepiece in and out of the diagonal until it is focused on infinity. The thumbscrew is then tightened to hold that focus. A diopter ring on the eyepiece allows you to fine-tune the focus for individual observers without having to loosen the thumbscrew or move the eyepiece.
