4
5
purpose. Separate refractor optical tube assemblies, such as the Orion
Short Tube 80, make excellent guide scopes.
The only exception to using a guide scope is to is use an off-axis guid-
er, which is typically made for Schmidt-Cassegrain telescopes (Figure
1b). The off-axis guider uses a prism to intercept a small portion of the
light path in front of the camera, thus allowing the camera and guider
to use the same telescope. Off-axis guiders require a large amount of
inward focus travel which is why they are generally only suitable for
Schmidt-Cassegrain telescopes.
Mount
An equatorial mount with dual
axis motors and a RJ-12 autogu-
ide port is required. Just about
any equatorial mount equipped
with an autoguide port will work
with the SSAG (Figure 3a).
The SSAG is “ST-4" compatible
which uses the same pin out
configuration as the first genera-
tion CCD autoguiders (Figure
3b). Most computerized goto
mounts also have this autoguide
port. For short exposure deep
space photography (typically
45 seconds or less) the SSAG
can successfully guide with a
computerized altitude-azimuth
or fork mounted telescope,
popular among computerized
Schmidt-Cassegrain telescopes.
However, guided exposures
longer than one minute in an alti-
tude-azimuth mount will cause
field rotation to occur in the
image (Figure 4). An equatorial
mount will yield the best overall
performance for guided deep
space astrophotography.
Figure 2.
Adjustable guide scope tube rings allow you to adjust the position of
the guide scope without moving the main imaging scope.
Adjustable guide scope tube rings
Figure 3a.
The SSAG works with
any mount equipped with an ST-4
compatible autoguide port, shown here
on the Sirius EQ-G mount.
Figure 3b.
This is the pin diagram
for the SSAG and ST-4 compatible
mounts.
Figure 4.
Field Rotation occurs in
long exposure images taken with an
altitude-azimuth mount or poorly polar
aligned equatorial mount.
Auto guider port
