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used or the image will be blurred beyond recognition. Try expo-
sure times between 1 and 10 seconds, depending upon the
brightness of the planet to be photographed and the ISO of the
film being used.
"Piggybacking Photography"
The Moon and planets are interesting targets for the budding
astrophotographer, but what next? Literally thousands of deep-
sky objects can be captured on film with a type of astrophotography
called "piggybacking." The basic idea is that a camera with its own
camera lens attached rides on top of the main telescope. The
telescope and camera both move with the rotation of the Earth
when the mount is polar aligned and the motor drive is engaged.
This allows for a long exposure through the camera without hav-
ing the object or background stars blurred. In addition to the motor
drive (dual-axis), an illuminated reticle eyepiece is also needed.
The T-ring and camera adapter are not needed, since the camera
is exposing through its own lens. Any camera lens with a focal
length between 35mm and 400mm is appropriate.
On top of one of the tube rings is a piggyback camera adapter.
This is the black knob with the threaded shaft protruding
through it. The tube ring with the piggyback adapter should be
closest to the objective end of the telescope. Remove the tube
rings from the equatorial mount and swap their positions, if
necessary. Now, connect the camera to the piggyback adapter.
There should be a 1/4"-20 mounting hole in the bottom of the
camera's body. Thread the protruding shaft of the piggyback
adapter into the 1/4"-20 mounting hole in the camera a few
turns. Position the camera so it is parallel with the telescope
tube and turn the knurled black knob of the piggyback adapter
counter-clockwise until the camera is locked into position.
Aim the telescope at a deep-sky object. It should be a fairly
large deep-sky object, as the camera lens will likely have a
wide field of view. Check to make sure that the object is also
centered in the camera's viewfinder. Turn the motor drive on.
Now, look into the telescope's eyepiece and center the brightest
star within the field of view. Remove the eyepiece and insert the
illuminated reticle eyepiece into the telescope's star diagonal.
Turn the eyepiece's illuminator on (dimly!). Recenter the bright
star (guide star) on the crosshairs of the reticle eyepiece. Check
again to make sure that the object to be photographed is still
centered within the camera's field of view. If it is not, recenter it
either by repositioning the camera on the piggyback adapter, or
by moving the main telescope. If you move the main telescope,
then you will need to recenter another guide star on the illumi-
nated eyepiece's crosshairs. Once the object is centered in the
camera and a guide star is centered in the reticle eyepiece, you're
ready to shoot.
Deep-sky objects are quite faint, and typically require expo-
sures on the order of 10 minutes. To hold the camera's shutter
open this long, you will need a locking shutter release cable.
Set the camera's shutter to the "B" (bulb) setting. Depress the
locking shutter release cable and lock it. You are now expos-
ing your first deep-sky object.
While exposing through the camera lens, you will need to
monitor the accuracy of the mount's tracking by looking through
the illuminated reticle eyepiece in the main telescope. If the
guide star drifts from its initial position, then use the hand con-
troller of the motor drive to "move" the guide star back to the
center of the crosshairs. Any drifting along the Dec. axis is a
result of improper polar alignment, so if the guide star drifts
greatly in Dec., the mount may need to be polar aligned more
accurately.
When the exposure is complete, unlock the shutter release
cable and close the camera's shutter.
Astrophotography can be enjoyable and rewarding, as well as
frustrating and time-consuming. Start slowly and consult out-
side resources, such as books and magazines, for more
details about astrophotography. Remember...have fun!
8. terrestrial Viewing
The AstroView 120ST Refractor may also be used for long-dis-
tance viewing over land. For this application we recommend
substitution of an Orion 45° Correct-Image Diagonal for the 90°
star diagonal that comes standard with the telescope. The cor-
rect-image diagonal will yield an upright, nonreversed image and
also provides a more comfortable viewing angle, since the tele-
scope will be aimed more horizontally for terrestrial subjects.
For terrestrial viewing, it's best to stick with low powers of 50x
or less. At higher powers the image loses sharpness and clar-
ity. That's because when the scope is pointed near the
horizon, it is peering through the thickest and most turbulent
part of the Earth's atmosphere.
Remember to aim well clear of the Sun, unless the front of the
telescope is fitted with a professionally made solar filter and
the finder scope is covered with foil or some other completely
opaque material.
9. Care and Maintenance
If you give your telescope 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. Do not store the tele-
scope outdoors, although storage in a garage or shed is OK.
Small components like eyepieces and other accessories
should be kept in a protective box or storage case. Keep the
cap on the front of the telescope when it is not in use.
Your AstroView 120ST telescope requires very little mechani-
cal maintenance. The optical tube is aluminum and has a
smooth painted finish that is fairly scratch-resistant. If a
scratch does appear on the tube, it will not harm the tele-
scope. If you wish, you may apply some auto touch-up paint to
the scratch. Smudges on the tube can be wiped off with a soft
cloth and a household cleaner such as Windex or Formula
409.
Cleaning the Optics
A small amount of dust or a few specks on the glass objective
(main) lens will not affect the performance of the telescope. If dust
builds up, however, simply blow it off with a blower bulb, or lightly
brush it off with a soft camel hair brush. Avoid touching optical
surfaces with your fingers, as skin oil may etch optical coatings.
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