10
ments to alter the focus slightly, so be sure to refocus for any new astro-imaging
targets.
Choosing a Site for Astro-imaging
Once you have a focused image, you may find your image shifting and washed
out. This can be caused by many environmental factors. Poor seeing (movement of
molecules in the air, such as heat rising) and poor transparency (moisture, smoke,
or other sky contaminants) will all serve to reduce image quality. That is why most
major astronomical telescopes are on high mountains in thin air, to get above much
of the seeing and transparency problems. Also, wind will move your telescope and
affect images. Your eyes viewing through an eyepiece can change slightly to com-
pensate for disturbances like these, but the camera cannot. Keep these factors in
mind when choosing an observing site for astronomical imaging.
For the best astro-images, we recommend finding a location with dry air, some
altitude, and away from city or streetlights. Even a nearby hilltop in the countryside
can provide better viewing conditions than many convenient backyard locations
.
Loss of Camera Connection
If the computer connection to the camera is interrupted, you will need to re-estab-
lish connection. This can happen due to several reasons; if a cable becomes
unplugged, the computer “freezes”, or the software/hardware otherwise temporarily
loses the data coming from the camera.
To re-establish camera connection, first close the Orion AmCap program on your
computer. Then, unplug and re-plug the camera into the computer’s USB port.
Now, open Orion AmCap, and the
Live Video Window
should appear indicating
re-established connection between camera and computer.
Using Focal Reducers and Barlow Lenses
Focal reducers serve to decrease the focal length of your telescope. This increases
the field of view seen by the camera (decreases camera magnification). This can
be useful for obtaining images of wider objects, such as the full Moon or a land-
scape vista.
Barlow lenses, or other tele-extenders, increase the focal length of your telescope,
which makes the camera field of view narrower (increases camera magnification).
This is useful for high-power planetary images. Keep in mind that when the focal
length is doubled, the image will become four times dimmer, so a longer exposure
may be necessary.
For best planetary imaging, you should shoot with an effective focal ratio (tele-
scope focal length ÷ telescope aperture) of F/20 or greater. This will give you a
good combination of image brightness and image scale for planets. For most
telescopes, a Barlow lens will be required to obtain this focal ratio. For example,
Schmidt-Cassegrain telescopes usually have a focal ratio of F/10. A 2x Barlow lens
doubles the effective focal length of the telescope, which makes the focal ratio f/20.
Similarly, a 3x Barlow lens will yield of focal ratio of F/30. You can also try using
multiple Barlows to obtain even greater effective focal ratios. There is a limit to