Astro Tech AT66ED Specifications
- ED doublet refractor optics: 66mm (2.6") aperture, 400mm focal length, f/6 focal ratio air-spaced doublet lens using premium Ohara glass from Japan, including an ED (Extra-low Dispersion glass) element to reduce spurious color halos and fringing to vanishingly low levels. While Astronomics does not claim fully apochromatic performance, as the manufacturer does, the scope is so free from spurious color as to be virtually indistinguishable from an apochromatic system.
- Multicoated optics: The objective lens has the latest state-of-the-art broadband antireflection multicoatings on all four air-to-glass surfaces for high light transmission and excellent contrast. This can easily be seen by looking into the objective lens of the scope. Virtually no reflection of your face will be seen. It's a sure sign that the high transmission coatings are doing their job, by letting virtually all the light enter the scope, rather than reflecting some light back to your eye.
- Internal light baffles: There are ten contrast-enhancing light baffles in the optical tube, for truly dark sky backgrounds and high terrestrial contrast. In addition, the edges of the objective lens are blackened to eliminate contrast-reducing stray internal reflections.
- Full power range capability: The "highest useful magnification" listed above right is 133x. This is the power obtained with a 3mm eyepiece, which provides an exit pupil of 0.5mm (about 1/50th of an inch) and 51x per inch of aperture. This is generally the smallest exit pupil recommended with any telescope before the images start to become too dim to be consistently useful.
Higher powers are possible for lunar and planetary observing, however, given reasonable seeing conditions. We've used the AT66ED on Saturn with a 4.8mm TeleVue Nagler and a Burgess/TMB 1.9x Optical Corrector Assembly (Barlow). This equals an effective focal length of 2.53mm and a magnification of 158x (61x per inch of aperture). Spurious color was still vanishingly low and apo-like with this combination. The image was still sharp and contrasty, although relatively dim (as you would expect with a 66mm aperture). Still higher magnifications are probably possible under excellent seeing conditions, although the increasing dimness of the image will start to limit the performance on all but the brightest objects.
The lowest useful power is 10x, achieved with a 40mm eyepiece (a 40mm TeleVue Plössl will give you a 4.2° field at that power). At 3.85x per inch of aperture, this is close to the 4x per inch of aperture generally regarded as the lowest practical power with any telescope. A 40mm eyepiece on the AT66ED will give you a 6.67mm exit pupil, larger than most eyes can dilate. Any lower power would simply waste some of the scope's light gathering capacity, as its collected light would fall on your iris, rather than entering your eye.
- Dew shield: A self-storing retractable dew shield slows the formation of dew on the lens in cold weather to extend your undisturbed observing time. It also improves the contrast, similar to the effect of the lens shade on a camera lens, when observing during the day or when there is excessive ambient light at night, such as a neighbor's backyard security light.
- Dual speed microfine Crayford-style focuser with 1.25" adapter: The precision-made focuser has dual-speed focusing. There are two coarse focusing knobs. The right knob also has a smaller concentric knob with 11:1 ratio reduction gear microfine focusing. This provides exceptionally precise image control during visual observing or critical 35mm or CCD imaging. The focus knobs have ribbed gripping surfaces so they are easy to operate, even while wearing gloves or mittens in cold weather. The 60mm (2.36") travel focuser drawtube has a scale marked in 1mm increments so you can note individual focuser positions for easy return to the correct focus when switching between visual use and photography. A lock knob under the focuser lets you lock in your photographic focus.
The focuser drawtube terminates in a standard 2" SCT-type rear cell thread to allow the use of any SCT photographic or visual accessory (2" SCT star diagonal, T-adapter, etc.) A locking ring on the body of the scope allows the focuser to be rotated a full 360°. This lets you rotate the focuser to line up a camera in either a landscape or portrait orientation (or any orientation in between), as well as put a star diagonal and eyepiece into the most comfortable observing position, and then temporarily lock the focuser in that position.
The supplied 1.25" eyepiece adapter threads onto the drawtube's 2" SCT threads and uses a soft brass compression ring to hold 1.25" star diagonals and accessories in place. The compression ring won't scratch the barrel of your star diagonal as an ordinary thumbscrew can.
- Combined equatorial dovetail/tripod adapter: The AT66ED has a removable L-shaped dovetail mounting shoe/tripod adapter. The 1.75" wide x 2.85" long mounting shoe is sized and shaped (with slanted sides) to fit the dovetail slot on the head of many equatorial mounts. It will fit, without modification, Celestron CG-5 and Advanced Series mounts, Meade LXD-75 mounts, and Vixen Great Polaris and Sphinx mounts, among others.
In addition, the mounting shoe has 1/4"-20 thread mounting holes that allow it to be installed on any camera tripod that has a standard 1/4"-20 thread mounting bolt. The bracket has two tripod mounting holes to allow you to balance the weight of a camera or heavy 2" eyepieces and accessories. The front hole balances the scope for 1.25" diagonal and 1.25" eyepiece use with the lens shade extended. The rear hole balances it when a camera or a 2" diagonal and 2" eyepiece are mounted.
Cork pads on the underside of the mounting shoe help keep the scope from swiveling when mounted on a tripod.
- Tube finish: The finish of the optical tube is a durable baked finish white paint with sleek anodized black trim.
- Other supplied accessories: A slip-on metal dust cap is standard. A threaded hole for installing a finderscope mounting shoe is located on the left side of the scope body in front of the focuser lock ring.
- Shipping/storage case: The scope comes in a 15.25" x 9.75" x 7.25" aluminum-clad locking hard case with carry handle. The foam-fitted case has cutouts for the scope, a 1.25" or 2" star diagonal, and up to three eyepieces (two 1.25" and one 2").
Astro-Tech is one of the very few manufacturers to provide a case at no charge for protection during shipping and as a storage convenience when the scope is not in use.
- Two year warranty: As an expression of the confidence Astronomy Technologies has in the quality of their products, the AT66ED is protected by a two-year limited warranty against flaws in materials and workmanship (shipping case excluded).
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