Flat Fields - Orion StarShoot Pro V2.0 Instruction Manual

15a.
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.
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
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15b.
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.
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