This all-black Astro-Tech 10 x 50mm illuminated finderscope is an excellent replacement for the straight-through dark crosshair finder supplied with many Celestron telescopes. It can also replace the smaller finders that often come with other brands and types of scopes.
The image-erecting amici prism built into the Astro-Tech’s right-angle diagonal gives you images that are correctly oriented (upright and right-reading), so that star patterns are seen exactly the way you see them on star charts and with your bare eye. This makes star-hopping from object to object using the Astro-Tech finder easier than with a mirror-image or inverted finderscope view.
The Astro-Tech’s right-angle right-reading/erect image optics also allow you to view near the zenith in comfort with the finder, without having to turn your head upside down, as you do with the standard straight-through inverted-image finder supplied with most scopes.
The finder’s image-erecting diagonal has precise helical focusing and a compression ring eyepiece holder. Both are premium touches rarely found in a finderscope. There is a dust cap for the eyepiece holder.
The finder’s field of view is a full 5° and its 50mm aperture has a limiting magnitude of 11, fainter than the stars on any commercial star chart. This makes it easier for you to locate faint nebulas and galaxies.
Eye relief is a very long 20mm that is ideal for unvignetted eyeglass use. There's a rubber eyecup that rolls down for eyeglass use and rolls up to shield your eye from contrast-reducing ambient light when used without glasses.
The Astro-Tech finder weighs 26 ounces, including eyepiece and illuminator, but without optional finder bracket. The finder is aluminum, anodized flat black. It is internally baffled for higher contrast. The integral dew shield is extra long to retard the formation of dew and shield the objective from ambient light. There is a thread-in dust cover for the dew shield and objective, another premium touch rarely seen in competitive finders.
Please note: The 62mm diameter body of the finder will not fit into the standard 50mm finder dovetail supplied with most Celestron scopes. A larger i.d. dual ring quick release dovetail bracket (#ATF50QRB) is available as an option. Also available as an option is the Astro-Tech #AT90GSR guidescope ring set which has the benefit of being able to hold either the finder or a small photoguide scope for astrophotography.
The supplied single crosshair illuminated reticle eyepiece is removable and has a standard 1.25" barrel. This allows you to remove it from the finder and also use it for centering stars in your main optics for polar alignment and go-to system alignment, for collimating your finder precisely with your main optics, for lining up guide stars in a photoguide scope and/or targeting objects for astroimaging, etc. A diopter ring on the eyepiece allows you to focus the crosshairs precisely to match your eyesight.
The illuminator for the eyepiece crosshairs has a combined on/off switch and rotary variable brightness control. The illuminator uses common A76/LR44/SR44 button-type batteries (supplied) which are easily replaced when needed. While the manufacturer 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.