Astro-Tech 8" f/4 imaging Newtonian optical tube
This 8" Astro-Tech AT8IN
optical tube is a very fast focal ratio f/4 reflector that has been
optimized for high-contrast wide field deep space imaging. It also
works well for spectacular wide field deep space visual observing,
as well as high contrast solar system visual observing and imaging.
It can be used with 1.25" and 2" eyepieces, 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 AT8IN is
well-suited to deep space and solar system visual observing as well
as solar system imaging. The 800mm 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
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.
Shown below, in the “Images of Some Features" section, are two first
light images through the AT8IN taken by Shawn Killian in central
Pennsylvania. According to Shawn, these first light images were not
processed except for a histogram stretch and a little unsharp
masking. Each is a single 10 minute guided exposure using an Orion
StarShoot Pro v2 camera and an Orion Atlas go-to mount. As first
light images, they show very clearly the imaging potential inherent
in the Astro-Tech AT8IN.
This Astro-Tech Telescope’s Optical System
Newtonian reflector optics: 8" aperture, 800mm focal length, f/4
focal ratio, parabolic primary mirror; 70mm m.a. elliptical diagonal
mirror. The 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 large 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 precisely center-spotted.
Built-in cooling fan: A low-vibration/high CFM fan is mounted on the
primary mirror cell. The fan is powered by a supplied battery pack
that uses eight user-supplied AA batteries. Alternatively, the fan
can be powered by a 12 VDC rechargeable battery if one is being used
to power your mount’s drive system.
Extended optical tube with 15 internal baffles: To increase the
contrast, the optical tube of the Astro-Tech AT8IN is extended 8.75"
forward of the focuser centerline to act as a lens shade to keep
ambient light from hitting the diagonal mirror. In addition, there
are 15 internal knife-edge baffles installed down the interior
length of the optical tube to eliminate any stray light that might
get past the extended optical tube and lower the contrast. The
baffles and tube interior are finished in matte black to further
absorb stray light. The result is exceptional contrast, far better
than a conventional reflector for both imaging and visual observing.
The white-painted 32" long x 9" diameter (with 9.25" diameter
front and rear cells) Astro-Tech optical tube is fabricated of
rolled steel, to allow the mirrors to cool to ambient temperature
more quickly. 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.
2" dual-speed Crayford focuser: The precision-made 2" 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 two coarse focusing knobs. One knob also has a
smaller concentric knob with 10:1 ratio reduction gear microfine
focusing. This provides exceptionally precise focus control during
critical CCD imaging. The focus knobs have ribbed gripping surfaces
so they are easy to operate, even while wearing gloves or mittens in
cold weather. A drawtube tension knob on the side of the focuser
lets you adjust the drag on the focuser drawtube to hold various
equipment load weights while focusing. A second knob lets you lock
in a precise photographic focus.
The drawtube has 34mm (1.35") of travel. There is 80mm of back
focus available from the top of the focuser’s 2" accessory holder to
the image plane. A 2" diameter x 35mm long extension tube is
provided to match the back focus requirement to your particular
photographic application. The 35mm extension tube has a non-marring
compression ring eyepiece/accessory holder.
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 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 6mm metric hole on
the top of each ring. This allows you to install a separate dovetail
on top of the optical tube for mounting photo guide rings and a
guidescope or similar accessories piggyback on top of the AT8IN. The
lightweight optical tube (18 pounds tube only; 21.6 pounds with
rings and finderscope) rotates in its felt-lined die cast cradle
rings to bring the focuser and finder to the most comfortable
Finderscope: 8x 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.
Two-year warranty: All Astro-Tech telescopes have a two-year
Astro-Tech Imaging Newtonian optical tube has:
• very fast f/4 focal ratio 8" Newtonian
• contrast-enhancing extended tube length with 15 internal
• built-in cooling fan for faster primary mirror cooldown
• 2" dual-speed Crayford focuser with 2" and 1.25"
compression ring accessory adapters
• 8 x 50mm finderscope in a quick-release bracket
• dual split mounting rings