20
21
is the
Base filename
, and you choose to
Autosave
five images, then the
images will appear in the selected file folder as “OrionNebula1dark_0001.
fit”, “OrionNebula1dark_0002.fit”, “OrionNebula1dark_0003.fit”,
“OrionNebula1dark_0004.fit”, and “OrionNebula1dark_0005.fit”. Using the
word “dark” in the
Base filename
will help you distinguish between light
and dark frames when combining later.
6. Click
Expose
, and Maxim DL Essentials will indicate the camera needs to
be covered to take a dark frame. Cover the front of the telescope you are
imaging through, and then click
OK
. The camera will commence taking
and saving the dark frames. You will calibrate your images with these dark
frames later see “Dark Frame Calibration”.
Flat Fields
A flat field is an image taken with uniform featureless light entering the tele-
scope, such as a blue sky in the early morning or after sunset. Flat fields solve
a number of issues in your astro-images.
Vignetting
Vignetting (Figure 15a) in a telescope reveals edge-darkening in the astro-
image. The large CCD chip in the StarShoot Pro can easily detect vignetting
through almost any telescope, even specialized astrographs. Vignetting is
more apparent when the telescope’s illuminated field is not large enough to
illuminate the full area of the CCD chip. As a result, more light is detected in
the center of the image compared to the edge.
Dust and Particles
Dust and particles (Figure 15b) will inevitably show up in your raw astro-imag-
es. Large particles on the CCD optical window sometimes look like unfocused
circles or doughnuts in your images. It’s too late to clean your camera if you
are already imaging in the field at night. And even when the camera is clean,
dust usually finds a way to show up in your images.
Telescope Artifacts
Very large particles or other artifacts in your telescope can effect your astro
images. Insufficient telescope baffling or poor collimation can also cause
unsymmetrical field illumination in your images.
To take a flat field image:
1. Ensure that the telescope is focused and ready for astro-imaging.
2. Point the telescope at a uniform and featureless light source, like the sky
at dusk or dawn, or a blank white sheet of paper. Make sure the camera
orientation is exactly the same as it is or was for astro-imaging (Although
the telescope is pointing at a featureless surface, the focus and orientation
must be set as it normally would be for astro-images.)
3. Set the
Mode
in the
Camera Control
window to
Light Raw 1x1
.
4. Select
Single
in the box beneath
Mode
.
5. Set the
Seconds
to 0.1 for now and click
Expose
. You want the
Max Pixel
to read somewhere around 20000. Adjust the exposure time as needed
until the
Max Pixel
is close to 20000.
6. Select
Autosave
(5-10 images) in the box beneath
Mode
.
7. Choose a file name to save your flat fields. You should include “flat” in the
file name to easily find it later, e.g. “OrionNebulaFlat”.
The flat fields also need dark frames.
8. Set the
Mode
in the
Camera
Control window to
Dark Raw 1x1
.
9. Rename the
Autosave
file to include “darkflat” so you can easily find the
file later when calibrating.
10. Use the same exposure time as your flat field and click
Expose
.
light and Dark 2x2 Modes
For added convenience and versatility, the StarShoot Pro’s individual pixels
(light-detecting sites) can be “binned” into units of two-by-two pixels (i.e. four
individual pixels create one binned 2x2 pixel). This creates larger and more
sensitive pixels, but with decreased resolution. This can be useful for some
types of astronomical imaging, such as capturing faint nebulae. It can also be
useful for quickly checking the image centering and orientation before using
the normal
Light Raw 1x1
mode to actually capture images.To use in “2x2”
mode, select
Light Mono 2x2
mode for capturing “light” images, and
Dark
Mono 2x2
mode to capture dark frames for averaging and subtracting. Images
can be combined and processed in the same way as
Light Raw 1x1
images.
Figure 15a.
Larger format CCD cameras like the StarShoot Pro reveal vignetting
through most telescopes. Vignetting occurs when the edge of the image plane has less
illumination than the center.
Figure 15b.
Dust or other particles on the camera’s optical window can show up as
distracting dark shapes in your images.
15a.
15b.