2" SCT-style rear cell threads on focuser drawtube
1.25" compression ring eyepiece adapter
Dovetail mounting shoe/tripod adapter
Retractable dew shield
Choice of tube colors
Foam-fitted aluminum-frame hard case
Two-year warranty
MSRP:
$349.00
Highest Useful Magnification:
133x
Focal Length:
400mm
Focal Ratio:
f/6
Resolution:
1.75 arc seconds
Visual Limiting Magnitude:
11.6
Aperture:
2.6"
Weight:
3.9 lbs.
The Astro-Tech AT66 uses an ED (Extra-low Dispersion glass) element in its 66mm (2.6”) optical system to reduce spurious color halos and fringing to vanishingly low levels. While the inexpensive 400mm f/6 AT66 is technically an apochromatic optical system, we won’t claim it is an apo in the class of a multiple thousand dollar Takahashi, Astro-Physics, or TMB refractor. However, the optical performance of this compact telescope is surprisingly close to the color-free performance of high end apo refractors that are many times its modest price.
The air-spaced doublet objective lens has the latest state-of-the-art antireflection multicoatings on all four air-to-glass surfaces for high light transmission and excellent contrast. Looking into the objective lens of the scope, you see virtually no reflection of your face. It’s a sure sign that the high transmission coatings are doing their job of letting virtually all the light enter the scope, rather than reflecting some light back to your eye.
There are ten light baffles in the optical tube to eliminate off-axis ambient light, 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.
The AT66 has a finely-machined dual speed Crayford-style focuser. There are two normal speed focusing knobs. The right knob also has a smaller concentric knob with 11:1 ratio reduction gear for 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 focuser drawtube has a full 60mm (2.36”) of travel. There’s a scale marked in 1mm increments on the drawtube 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 the photographic focus.
The focuser drawtube terminates in a standard 2” SCT-type rear cell thread to allow the use of any Schmidt-Cassegrain photographic or visual accessory (a 2” SCT star diagonal, T-adapter, etc.) A simple turn of the knurled ring on the scope body allows you to rotate the focuser a full 360° to put your eyepiece in the most comfortable observing position, or to line up a camera in a landscape or portrait orientation. A turn of the ring in the opposite direction locks the focuser at the desired angle.
The supplied 1.25” eyepiece adapter threads onto the drawtube’s 2” SCT threads. It 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.
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.
The AT66 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 the scope to be used on any camera tripod that has a standard 1/4”-20 thread mounting bolt. Cork pads on the underside of the mounting shoe help keep the scope from swiveling when mounted on a tripod. 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.
Two hex head bolts hold the mounting shoe in place on the 75mm diameter optical tube. This allows the shoe to be removed and reversed to better balance very tail-heavy accessory combinations. Removing the mounting shoe also lets you install the AT66 in user-supplied optional mounting rings for use on an equatorial mount or as a piggyback photoguide or super finder.
A 3mm eyepiece gives a highest useful magnification of 133x – 51x per inch of aperture, with an exit pupil of 0.5mm (about 1/50th of an inch). This is generally the smallest exit pupil recommended with any telescope before the images become too dim to be consistently useful. Higher powers are possible for lunar and planetary observing, however. The AT66 can often be used on Jupiter and Saturn at magnifications of 160x (61x per inch of aperture) or more, given a well-placed planet and good seeing conditions. Spurious color will still be vanishingly low at this power, with images that are still sharp and contrasty, although dim (as you would expect with a 66mm aperture). Still higher magnifications are theoretically possible, although the increasing dimness of the image will rapidly limit the performance.
A 40mm eyepiece gives a lowest useful power of 10x (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. At this power, the eyepiece has 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.
The optical tube is available finished in a variety of liquid anodized colors to suit your personal preferences. You can choose from black for inconspicuous mounting on a Celestron SCT as a photoguide scope or super finder. It is also available in blue to mount inconspicuously on a Meade SCT. To express your individuality, you can get the AT66 in red, forest green, or a handsome copper-tinted burnt orange. It is even available in a striking anodized chrome finish that will stand out at any star party or observing session. For the traditionalist, it is also available in either a classic textured off-white paint or a brass-look anodized finish. All of the colors are set off by a black focuser and gloss black trim.
A slip-on metal dust cover is standard. The scope comes in a 15” x 10” x 6.25” aluminum-frame locking hard carrying 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”).
The 11.5” long optical tube (14.25” long with the lens shade extended) of the AT66 has the right balance of aperture and focal length to use as a low-power rich field telescope, as a medium-power planetary telescope, or as any kind of telescope in between. Its compact size, light weight, and convenient removable L-shaped mounting shoe that fits any photographic tripod also make it an excellent terrestrial spotting scope for travel, birding, or nature studies. In addition, optional camera adapters turn the AT66 into a superb 400mm (8x) f/6 telephoto lens.
If Astronomy Technologies AT66 was just another 66mm refractor, the quality of its optics alone would still make it a superb value. Add the unique features – like the dual speed microfine focuser, your choice of colors, and a hard case – and you have a scope that has absolutely no equal at its very affordable price.
As an expression of the confidence we have in the quality of our Astronomy Technologies products, the Astro-Tech AT66 is protected by a two-year limited warranty against flaws in materials and workmanship.
