6
Focusing the Telescope
Insert the 25mm Explorer II eyepiece into the focuser and
secure with the thumbscrew. Move the telescope so the front
(open) end is pointing in the general direction of an object at
least 1/4-mile away. Now with your fingers, slowly rotate one
of the focusing knobs until the object comes into sharp focus.
Go a little bit beyond sharp focus until the image starts to blur
again, then reverse the rotation of the knob, just to make sure
you've hit the exact focus point.
Do You Wear Eyeglasses?
If you wear eyeglasses, you may be able to keep them on
while you observe. In order to do this, your eyepiece must
have enough “eye relief” to allow you to see the entire field of
view with glasses on. You can try this by looking through the
eyepiece first with your glasses on and then with them off, and
see if the glasses restrict the view to only a portion of the full
field. If the glasses do restrict the field of view, you may be
able to observe with your glasses off by just refocusing the tel-
escope the needed amount.
If your eyes are astigmatic, images will probably appear the
best with glasses on. This is because a telescope’s focuser can
accommodate for nearsightedness or farsightedness, but not
astigmatism. If you have to wear your glasses while observing
and cannot see the entire field of view, you may want to pur-
chase additional eyepieces that have longer eye relief.
Aligning the Finder Scope
The finder scope must be aligned accurately with the tele-
scope for proper use. To align it, aim the main telescope in the
general direction of an object at least 1/4-mile away, such as
the top of a telephone pole, a chimney, etc. Do this by first
loosening the R.A. and Dec. lock knobs. Position the tele-
scope so the object appears in the eyepiece's field of view and
then retighten the R.A. and Dec. lock knobs. Use the slow-
motion control cables to center the object in the eyepiece.
Now, look in the finder scope. Is the object visible? Ideally, it
will be somewhere in the finder’s field of view. If it is not, some
coarse adjustments of the three black nylon finder scope
alignment thumbscrews will be needed to get the finder scope
roughly parallel to the main tube. If this does not work, loosen
the two thumbnuts that secure the finder scope bracket to the
optical tube and slide the bracket left or right to get the object
in the finder’s field of view. Retighten the thumbnuts.
Note: The image in both the finder scope and the main tele-
scope will appear upside-down (rotated 180°). This is normal
for finderscopes and reflector telescopes (see Figure 4).
By loosening one alignment thumbscrew and tightening the oth-
ers, you change the line of sight of the finder scope. Use the
three alignment thumbscrews to center the object on the
crosshairs of the finder scope. Look again into the telescope's
eyepiece and see if the object 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 finderscope.
The finder scope alignment needs to be checked before every
observing session. This can easily be done at night, before
viewing through the telescope. Choose any bright star or plan-
et, center the object in the telescope eyepiece, and then
adjust the finder scope's alignment thumbscrews until the star
or planet is also centered on the finder's crosshairs. The find-
er scope is an invaluable tool for locating objects in the night
sky since it has a much wider field-of-view than the main tele-
scope tube.
Figure 5. To find Polaris in the
night sky, look north and find the
Big Dipper. Extend an imaginary
line from the two “Pointer Stars” in
the bowl of the Big Dipper. Go
about five times the distance
between those stars and you’ll
reach Polaris, which lies within 1°
of the north celestial pole (NCP).
Big Dipper
(in Ursa Major)
Little Dipper
(in Ursa Minor)
N.C.P.
Poin
ter S
tars
Polaris
Cassiopeia
Naked-eye view
View through finder scope and telescope
Figure 4. The view through a standard finder
scope and reflector telescope is upside down.
This is true for the SpaceProbe 3 and its finder
scope as well.
