ORION TELESCOPES & BINOCULARS ShortTube 80 User manual

IN 651 8/20
INSTRUCTION MANUAL
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AN EMPLOYEE-OWNED COMPANY
Orion ShortTube™80 Refractor
Optical Tube Assemblies
#9948 ST80 OTA only
#9947 ST80-A (Astronomical)
#9946 ST80-T (Terrestrial)
#9948
#9947
#9946

2
WARNING: Do NOT look at the Sun without a
professionally made solar lter on the telescope;
serious eye damage may result if you look at the
Sun with any unltered optical instrument. Do not
leave the telescope unsupervised around children.
Always cover the lenses when leaving the telescope
in direct sunlight.
Contents
I. General Information ..................... 2
II. The ShortTube 80 OTA (#9948) ............ 3
III. ShortTube 80-A (#9947) ................. 3
IV. ShortTube 80-T (#9946) ................. 6
Figure 1. The 1.25" rack-and-pinion focuser of the ShortTube 80.
Figure 2. A DSLR camera can be attached directly to the
ShortTube 80’s drawtube collar with the use of a T-ring (sold
separately) for your particular camera.
Congratulations on your purchase of an Orion ShortTube 80
Refractor Optical Tube Assembly! This versatile, time-tested
rich-eld refractor excels for a wide variety of applications,
both celestial and terrestrial. Compact, portable, and easy to
use, The ShortTube 80 will provide many hours of enjoyment
for novice and experienced astronomers alike.
This manual covers three different congurations of ShortTube
80 OTA: the ST80 (OTA) without any accessories; the ST80-A,
congured for comfortable astronomical observation; and the
ST80-T, optimized for terrestrial viewing. The rst part of the man-
ual contains information that pertains to all three congurations.
After that are sections devoted to each model specically.
I. General Information
Collimation
The optical elements of all ShortTube 80 telescopes are pre-
cisely aligned (collimated) at the factory to provide the sharp-
est images possible. No further optical adjustment is neces-
sary.
Dovetail nder
scope shoe
Focus wheel
Thumbscrews
T-threads
Focus wheel
Focus lock
Drawtube
collar
Drawtube
collar
T-ring (M42)
Focusing the Telescope
The ShortTube 80 is outtted with a 1.25" rack and pinion fo-
cuser. To focus the image you will use the black focus wheels
(Figure 1). Assuming you have installed a diagonal and eye-
piece to acquire a target image, turn the focus wheels to rack
the focuser drawtube in and out, changing the focal distance
of the light path. To ensure the sharpest focus go slightly past
your perceived focus point and then reverse directions until
you have a sharp focus.
You will have to readjust the focus when aiming at subjects
of varying distances, or after changing eyepieces. Make sure
the focus lock thumbscrew is loosened before focusing. After
focusing, you can tighten it to lock the telescope’s focus into
place if desired.
1.25" Drawtube Collar
The ShortTube 80’s focuser drawtube is equipped with a 1.25"
collar (Figure 1) into which a diagonal or other 1.25" acces-
sories are secured. Loosen the two thumbscrews and insert
the accessory’s barrel into the drawtube collar until it stops,
then secure it in place by re-tightening the thumbscrews. The
male threads on the end of the collar are T-threads (M42). Any
accessory with a female T-thread such as many commercially
available CCD and CMOS imagers and T-rings for SLR/DSLR
camera bodies can be coupled to the ShortTube 80 by thread-
ing it directly onto the collar (Figure 2). This method is often
preferred over inserting a camera’s nosepiece barrel into the
collar and securing it with the thumbscrews because thread
coupling provides a rmer connection.

3
Figure 3. The ShortTube 80 OTA makes a popular guide scope for
astrophotography.
“Play” in the Focuser Drawtube? Here’s How to
Adjust it Out
If your telescope that has a little bit of “play”, or looseness, in
the focuser drawtube, rest assured that you can make a quick
adjustment to remove it. Ideally, you don’t want any drawtube
play as it could produce some shifting of the image in the eye-
piece as you rack the focuser in or out using the focus wheels.
Such play could also throw a sharp image out of focus.
If you feel any wiggling of the drawtube in the focuser hous-
ing when you grab the end of the drawtube and tug it up and
down, then do the following. You will need a 1.5mm metric
Allen key to make this adjustment.
Locate the two tiny holes on the top of the focuser (circled in
Figure 1). Insert the end of a 1.5mm Allen key into the hole
closest to the focus wheels and turn the setscrew clockwise
about 1/8 of a turn. Now try tugging the drawtube up and down
again. Usually that 1/8 turn of tightening does the trick, but if
there is still some looseness in the drawtube, tighten the set-
screw another 1/8 turn. You could also try tightening the other
setscrew 1/8 turn as well, but usually it only requires tightening
one.You should only have to make this adjustment once.
Care and Maintenance
If you give your ShortTube 80 reasonable care, it will last a life-
time. Store it in a clean, dry, dust-free place, safe from rapid
changes in temperature and humidity. Keep the dust cover on
the front of the telescope when it is not in use. The ShortTube
80 OTA requires very little mechanical maintenance. The optical
tube is aluminum and has a smooth painted nish that is fairly
scratch-resistant. If a scratch does appear on the tube, it will not
harm the telescope. Smudges on the tube can be wiped off with
a soft cloth and a household cleaner such as Formula 409.
Cleaning Lenses
Any quality optical lens cleaning tissue and optical lens clean-
ing uid specically designed for multi-coated optics can be
used to clean the telescope’s objective lens. Never use regular
glass cleaner or cleaning uid designed for eyeglasses. Before
cleaning with uid and tissue, blow any loose particles off the
lens with a blower bulb or compressed air. Then apply some
cleaning uid to a tissue, never directly on the optics. Wipe the
lens gently in a circular motion, then remove any excess uid
with a fresh lens tissue. Oily ngerprints and smudges may be
removed using this method. Use caution; rubbing too hard may
scratch the lens. Clean only a small area at a time, using a
fresh lens tissue on each area. Never reuse tissues.
II. The ShortTube 80 OTA
(#9948)
This version of the ShortTube 80 does not include any acces-
sories, thus allowing you to customize it with the accessories
of your choice. Many people use this model as a guide scope
for astrophotography. For attachment to a telescope for this
purpose, you will need tube rings (90mm diameter) or guide
scope rings, and a dovetail mounting bar, which are sold sepa-
rately.
To achieve focus with an eyepiece, a diagonal or extension
tube may be required. The same goes for achieving focus with
a guide camera, for which we recommend a 1.25" extension
tube. For the latter, insert the extension tube barrel into the
drawtube collar and lock it down with the two thumbscrews.
Then insert the 1.25" nosepiece of the guide camera into the
extension tube and secure it with the thumbscrew(s).
Specifications
Objective lens: Achromatic doublet, air-spaced
Objective lens coatings: Multi-coated
Aperture: 80mm
Focal length: 400mm
Focal ratio: f/5
Focuser: Rack-and-pinion, 1.25", accepts camera T-ring
Drawtube travel: 61mm
Backfocus distance (from end of drawtube collar): 114.9mm
Optical tube length: 15"
Optical tube diameter: 90.4mm
Assembled weight: 2 lbs., 11 oz.
III. ShortTube 80-A (#9947)
Parts List
Optical tube assembly, with tube rings and dovetail bar
installed
25mm Sirius Plossl 1.25" eyepiece (16x)
10mm Sirius Plossl 1.25" eyepiece (40x)
90° Mirror star diagonal, 1.25"
8x40 Finder scope
Finder scope bracket with O-ring
Objective lens cap
Hex key (5mm)

4
Installing the Finder Scope
The ShortTube 80-A comes with an 8x40 achromatic crosshair
nder scope (see Figure 4). The 8x40 descriptor means it has
8x magnifying power and a 40mm aperture.To place the nder
scope in the nder scope bracket (Figure 5), rst unthread the
two black nylon thumbscrews until the screw ends are ush
with the inside diameter of the bracket. Place the O-ring that
comes on the base of the bracket over the body of the nder
scope until it seats into the slot on the middle of the nder
scope. Slide the eyepiece end (narrow end) of the nder scope
into the end of the bracket’s cylinder opposite the adjustment
screws while pulling the chrome, spring-loaded tensioner on
the bracket with your ngers. Push the nder scope through
the bracket until the O-ring seats just inside the front open-
ing of the bracket’s cylinder. Now, release the tensioner and
tighten the two black nylon screws a couple of turns each to
secure the nder scope in place. Secure the bracket to the
dovetail shoe on the optical tube with the knurled thumbscrew
on the dovetail shoe (Figure 6).
Installing the Diagonal and Eyepiece
Insert the chrome barrel of the star diagonal into the eyepiece
holder and secure it with the two knurled thumbscrews. Then
insert the 25mm or 10mm eyepiece into the diagonal and tight-
en it with the two thumbscrews on the diagonal.
Mounting the Telescope
The Vixen-style dovetail mounting bar coupled to the tube
rings allows attachment of the telescope to any mount that
has a compatible Vixen-style dovetail saddle or to a tripod
equipped with a ¼"-20 post. For the latter, thread the tripod’s
1⁄4"-20 post directly into one of the threaded holes on the bot-
tom of the dovetail mounting bar.
Image Orientation
The image in the telescope will appear reversed left to right. This
is normal for astronomical telescopes that utilize a star diagonal.
The nder scope view will appear rotated 180° (Figure 7).
Aligning the Finder Scope
The nder scope is so named because it makes it easier to
nd the subject you want to observe in the main telescope.
That’s because the nder scope has a much wider eld of
view than that of the main telescope. Before you use the nder
scope, it must be precisely aligned with the telescope, so they
both point to exactly the same spot.
Alignment is easiest to do in daylight, rather than at night under
the stars. First, insert the lowest-power (25mm) eyepiece into
the main telescope’s focuser. Then point the telescope at a dis-
crete object such as the top of a telephone pole or a street
sign that is at least a quarter-mile away. Move the telescope so
the target object appears in the very center of the eld of view
when you look into the eyepiece. Now look through the nder
scope. Is the object centered in the nder scope’s eld of view,
i.e., on the crosshairs? If not, hopefully it will be visible some-
where in the eld of view, so only ne adjustment of the two
black nylon alignment screws will be needed. Otherwise you’ll
have to make coarser adjustments to the alignment screws to
redirect the aim of the nder scope. Use the two alignment
screws to center the object on the crosshairs of the nder
scope. Then look again into the main telescope’s eyepiece and
see if it is still centered there as well. If it isn’t, repeat the entire
process, making sure not to move the main telescope while
adjusting the alignment of the nder scope. Finder scopes can
come out of alignment during transport of the telescope, so
check the alignment before each observing session.
Focusing the Finder Scope
If, when looking through the finder scope, you notice that
the images appear out of focus, you will need to refocus the
Figure 4. The ShortTube 80-A is outtted for astronomical viewing.
Finder scope Bracket Objective lens cell
Piggyback
camera adapter
Tube rings
Tube ring clamping knobs
Star diagonal
Sirius Plössl
eyepiece
Dovetail mounting bar
Dew shield
Lock ring

5
Figure 5. Inserting the nder scope into the nder scope bracket.
nder scope for your eyes. First loosen the lock ring located
behind the objective lens cell on the body of the nder scope
(see Figure 4). Back the lock ring off by a few turns, for now.
Refocus the nder scope on a distant object by threading the
objective lens cell in or out of the nder scope body. Precise
focusing will be achieved by focusing the nder scope on a
bright star. Once the image appears sharp, retighten the lock
ring behind the objective lens cell. The nder scope’s focus
should not need to be adjusted again.
Piggyback Camera Adapter
The ST80-A comes with a piggyback camera adapter installed
on one of the tube rings (Figure 4). It comprises a ¼”-20 post
and a knurled disk. You can mount a DSLR or mirrorless cam-
era equipped with a lens to ride “piggyback” on the ShortTube
80 to take wide-eld photographs. To install the camera onto
the piggyback adapter, set the ¼"-20 socket on the bottom of
the camera onto the adapter’s threaded post and rotate the
camera a few turns. The rotate the knurled disk counterclock-
wise until it meets the camera bottom. Tighten the disk against
the camera bottom. Note that you may have to rst remove
and rotate the whole tube ring assembly so that the piggyback
adapter is in front, to avoid any contact between the camera
and the nder scope.
Specifications
Objective lens: Achromatic doublet, air-spaced
Objective lens coatings: Multi-coated
Aperture: 80mm
Focal length: 400mm
Focal ratio: f/5
Focuser: Rack-and-pinion, 1.25", accepts camera T-ring
Drawtube travel: 61mm
Backfocus distance (from end of drawtube collar): 114.9mm
Optical tube length: 15"
Optical tube diameter: 90.4mm
Tube rings: Pair of 90mm ID rings
Mounting bar: Vixen-style, 110mm length
Finder scope: 8x40 achromatic, crosshair
Eyepieces: 25mm (16x) and 10mm (40x) Sirius Plossl, 1.25";
barrels threaded for Orion lters
Star diagonal: Mirror type, 90 degrees, 1.25"; barrel threaded
for Orion lters
Assembled weight: 4 lbs., 10.6 oz.
Figure 6. To install the nder scope, slide the bracket foot forward
in the dovetail shoe, then tighten the thumbscrew on the shoe.
Figure 7. Images through the ShortTube 80-A with its star
diagonal in place will be reversed from left-to-right. Images
through the nder scope will appear upside-down and backwards
(rotated180°).
Naked-eye view
View through the ShortTube 80-A
Bracket
Dovetail
shoe
View through nder scope