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Stretch Window. The red slider arrow corresponds to the Minimum value and
the green arrow corresponds to the Maximum value. Simply left-click and then
drag each arrow to adjust it to the desired level. The best results are obtained
by adjusting the arrows (numbers) until the most pleasing display appears.
There are also seven automatic settings in the Screen Stretch Window.
Typically, Medium will give good results for deep sky objects, so the default
screen stretch setting is Medium.
Instead of using the Screen Stretch Window, it is faster to use the Quick
Stretch facility. This allows you to modify the image appearance instantly with
small up/down and left/right movements of the mouse. To do this, hold down
the Shift key, then left-click and drag the mouse on the image. You’ll find this
feature to be a great convenience when fine adjusting the screen stretch to get
an image to look its best.
The trick with stretching is determining exactly how to stretch the image for
best effect. Often there are several different possibilities for the same image.
Trial-and-error will be the best way to judge what the best screen stretch set-
ting is. Try several different settings until you find one you think looks best.
When the image is subsequently saved, the screen stretch setting information
will be kept when the image is next opened.
Astronomical Imaging
Now that you’re familiar with basic camera and software operation, it’s time to
take the SSDSI-II out at night under the stars to capture some astronomical
images. We recommend starting with the Moon, as it is easy to acquire into
the camera’s field of view, and typically does not require stacking of multiple
exposures as planetary and deep sky images do.
Imaging the Moon
Imaging the Moon is much like imaging terrestrial objects during the day. Since
the exposure is very short, it is not critical that the telescope mount be pre-
cisely polar aligned. Best focusing will be achieved by first focusing on a bright
star near the Moon. Start with short exposures of less than 0.1 seconds.
When the moon is past half full, it is hard to get detail due to the tremendous
glare off of the lunar surface. Most detail, even on a sliver of a moon, will be at
the terminator (the tiny thin line between the shadow and light, see Figure 12).
To get more of the moon in the image, a focal reducer will need to be used.
For close-ups of craters use a barlow lens (see “Using Focal Reducers and
Barlow Lenses”).
Imaging Planets
The best planetary images will be obtained by stacking (combining) many
individual images in order to improve image contrast, brightness, and detail.
Because the angular diameter of planets is quite small, you will need to use a
barlow lens between the SSDSI-II and telescope to extend the effective focal
length of the system and increase image scale (see “Using Focal Reducers
and Barlow Lenses”).
Since you will be taking multiple images over a period of time, it is important
the mount be polar aligned in order to keep the planet within the field of view
of the camera and to prevent image blurring due to poor tracking during each
exposure. To this end, you should also have the right ascension (R.A.) motor
drive engaged. Do not bother trying to obtain a perfect polar alignment, as that
will only be important for taking longer exposure images of deep sky objects;
most planetary exposures will be less than a few seconds.
To take multiple images of a planet for stacking:
1. Acquire the planet into the field of view of your telescope (barlow lens
attached) with an eyepiece and center the planet in the eyepiece’s field of
view. Focus the eyepiece with the telescope’s focuser.
2. Now, remove the eyepiece and replace it with the SSDSI-II.
3. In the Camera Control Window, set the Mode to Light Color 1x1. Set
Seconds (exposure time) to 0.5 seconds to begin with. In the box below
the Mode box, select Focus. Click the Expose button.
Figure 12. The Moon’s surface detail looks the best along the terminator.