This right-angle erect image finderscope is a sensible replacement for the straight-through inverted image 9 x 50mm finder supplied with many 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 the refractor and Schmidt-Cassegrain versions of the Celestron 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 smaller 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.
The finder includes an etched glass reticle with dual crosshairs forming a box in the center of the field, as shown in the feature images below. The red LED illuminator is powered by two 1.5V button-type watch/camera batteries (supplied and easily replaceable at any drug or department store). The illuminator has a combined on/off switch and brightness level control.
The finder’s 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 apparent field of view of the finder is 52°. Combine that with the 8x magnification and you get a very generous actual field of view of 6.5°. The eye relief is an acceptable 8mm, although the image will be somewhat vignetted for those who must wear eyeglasses while observing. There's a rubber eyecup to keep eyeglass wearers from scratching the lenses of their eyeglasses during use. The finder weighs 21.6 ounces, with illuminator but without optional finder bracket. It will fit into the standard 50mm finder bracket supplied with most Celestron scopes that come with a straight-through 9 x 50mm finder. If you’re upgrading from a smaller finder, reflector-type dual mounting rings and a quick release dovetail bracket are available as options. The 54.1mm 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. Dustcovers are supplied for both the objective lens and the eyepiece.
The supplied dual crosshair eyepiece, with attached illuminator, 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. A helical focusing ring on the eyepiece allows you to focus the finder on infinity to suit your individual eyesight. The finder will be focused for most observers when the helical focus ring is in the center of its range. Should you need a greater focusing range, you can loosen the thumbscrew in the diagonal’s eyepiece holder and slide the eyepiece in and out of the diagonal until it focuses properly for your eyesight, using the helical focus ring to fine-tune the focus further as needed. The thumbscrew should then be tightened to hold that focus.
Please note: While the manufacturer normally supplies batteries at no cost with this product as a convenience, the battery charge or useful life is not guaranteed. The batteries may arrive with their charge depleted or very low. In such a case, you will have to purchase replacement batteries locally, as battery life is not covered by the manufacturer’s warranty.