Astro-Tech 6" f/4 Imaging Newtonian Optical Tube
Manufacturer Part # AT6IN
This Astro-Tech Imaging Newtonian optical tube has:
Very fast f/4 focal ratio 6" Newtonian reflector optics
Contrast-enhancing extended tube length
2" dual-speed linear bearing Crayford focuser with 2" and 1.25" compression ring accessory adapters
8 x 50mm finderscope in a quick-release bracket
Dual split hinged mounting rings
This 6" Astro-Tech AT6IN optical tube is a very fast focal ratio f/4 reflector that has been optimized for very wide field deep space imaging. It can be used with 35mm cameras, DSLRs, web-cams, DSI-type cameras, and large format CCD cameras alike.
The light weight standard equipment mounting rings of the Astro-Tech Imaging Newtonian allow you to use it on a wide variety of dovetail plates and German equatorial mounts - from the most basic to the most elaborate high payload go-to system.
In addition to deep space imaging, the Astro-Tech AT6IN is also usable for solar system imaging as well as deep space and solar system visual observing. Solar system visual contrast will be somewhat reduced compared to a longer focal ratio reflector because of the AT6IN's larger secondary mirror that has been optimized for full-field photographic illumination. However, the visual performance will still be much more than acceptable, and the 610mm focal length of this Astro-Tech makes it quite possible to achieve the high powers needed for detailed lunar and planetary observing. Simply add optional 1.25" or 2" eyepieces, and perhaps an optional Barlow lens, and this Astro-Tech Imaging Newtonian will provide you with crisp and sharply detailed close-up views of the Moon and planets.
This Astro-Tech Telescope's Optical System . . .
Newtonian reflector optics: 6" aperture, 610mm focal length, f/4 focal ratio. Parabolic primary mirror. Both primary and diagonal mirrors are ground and polished under computer control for guaranteed diffraction limited performance, coated with 91% reflectivity aluminum, and overcoated with a protective layer of silicon dioxide (quartz) for long life.
The mirrors are made of B270 "water white" optical crown glass that is free of internal stress and striae. B270 glass is equivalent to BK7 in performance and optical quality. The thermal stability of B270 glass is generally better than the soda lime float glass used for the mirrors of most reflectors in this reasonable price range. For maximum contrast, the four secondary mirror spider vanes have been optimized to be as thin as possible without losing stability.
No-tool push-pull mirror cell: The die-cast aluminum primary mirror cell has six hand adjust push-pull collimation knobs. These make it easy to collimate the primary mirror without tools, even while wearing gloves or mittens in cold weather. To further ease collimation, the primary mirror is center-spotted.
Extended optical tube: To increase the contrast, the optical tube of the Astro-Tech AT6IN is extended 7.25" forward of the focuser centerline to act as a lens shade to keep ambient light from hitting the diagonal mirror. This results in higher contrast than a conventional reflector for both imaging and visual observing.
The white-painted 22.5" long x 7" diameter Astro-Tech optical tube (with 7.25" diameter front and rear cells) is fabricated of rolled steel, to allow the mirrors to cool to ambient temperature more quickly. While the rolled steel optical tube is a little heavier than a more-costly aluminum tube, a Sky & Telescope review of the AT6IN's 8" big brother AT8IN pointed out that a steel tube "also helps make it a very rigid setup, which is a good thing for astrophotographers." The scope's tube end rings are sturdy die-cast aluminum, to protect the tube during transport and provide exceptionally rigid support for the optics.
For essentially coma-free imaging with the AT6IN, consider adding the Astro-Tech ATCC coma corrector. This imaging accessory essentially eliminates the coma inherent in all fast focal ratio reflector telescope designs, so that the coma-free star images remain point-like all across the field.
2" dual-speed linear bearing Crayford focuser: The precision-made 2" linear bearing Crayford focuser drawtube ends in a 2" accessory holder. A 1.25" accessory adapter is standard equipment. Both the drawtube's 2" accessory holder and the 1.25" accessory adapter have non-marring compression ring eyepiece/accessory holders.
The focuser has dual-speed focusing. There are two coarse focusing knobs. The knob facing the rear of the scope also has a smaller concentric knob with a 10:1 reduction gear microfine focusing ratio. This provides exceptionally precise image control during critical imaging. All focus knobs are ribbed, so they are easy to operate, even while wearing gloves or mittens in cold weather. A lock knob underneath the focuser lets you adjust the tension on the drawtube to accommodate varying equipment loads. A large lock knob on top of the focuser lets you lock in your photographic focus.
The new linear bearing focuser has a polished stainless steel drive rail that runs the length of the underside of the drawtube. The focuser's stainless steel drive shaft presses on this drive rail to move the focuser, rather than having the hard steel drive shaft press directly on (and wear out) the softer aluminum drawtube as with conventional Crayford focusers. The steel drive rail rides in a self-lubricating track that extends almost the entire length of the focuser body. The drive rail and its attached drawtube are thereby supported over most of their length at all times, rather than by a conventional Crayford focuser's two sets of small contact area roller bearings. This system distributes the drive force evenly over the entire drawtube, without concentrating it on a few small contact points. The result is a very rigid drawtube with essentially zero flexure and no wear (much less flat spots or uneven wear) on the focuser drawtube.
The focuser drawtube has 51mm (2") of travel. A focusing scale on top of the focuser drawtube is marked in inches and millimeters to make it easy to return to the approximate correct focus when setting up to image or observe each night.
Split tube rings: A pair of die-cast aluminum hinged split tube mounting rings are provided. Each ring has a flat boss on its underside with a 1/4"-20 thread mounting hole, flanked by two 4mm metric holes on 30mm centers, for installing the ring on a Vixen-style or Losmandy-style "D-plate" dovetail mounting plate. This lets you mount the scope on virtually any equatorial mount. In addition, there is a flat boss with a 4mm metric hole on the top of each ring. This allows you to install a separate dovetail on top of the optical tube for mounting photoguide rings and a guidescope or similar accessories piggyback on top of the AT6IN. The lightweight optical tube (9 pounds 10 ounces without finderscope) rotates in its felt-lined die cast cradle rings to bring the focuser and finder to the most comfortable viewing position.
Finderscope: 8 x 50mm straight-through dark crosshair achromatic design, in a spring-loaded quick-release mounting bracket. The finder has a long and comfortable 13mm eye relief. To focus the finder, loosen the trim ring behind the objective lens cell, screw the lens cell in or out to focus, and tighten the trim ring to lock in the correct focus.
Tech Details:
| Aperture | 6" |
|---|---|
| Binary and Star Cluster Observation | Very Good |
| Focal Length | 610mm |
| Focal Ratio | f/4 |
| Galaxy and Nebula Observation | Good |
| Heaviest Single Component | 9 lbs. 10 oz. |
| Highest Useful Magnification | 203x |
| Lunar Observation | Great |
| Planetary Observation | Very Good |
| Resolution | 0.76 arc seconds |
| Visual Limiting Magnitude | 13.4 |
| Warranty | 1 year |