Orion 52085 instruction manual Flat Fields, Light and Dark 2x2 Modes

15a.15b.

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

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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