Set Arcsecond Scale
The Set Arcsecond Scale command attaches a linear arcsecond scale to the X and Y axes of the image. This gives you the option to get positional readout, plots, and measurements in units of either arcseconds or pixels. This command can also use the Calculate Image Scale command to calculate a value for the camera and telescope combination. The value is inserted into the Scale field in the dialog, after which you would use [Apply] or [OK] to apply it to the image or image set.
The Set Arcsecond Scale command opens
from the Image Window > Coordinates menu and 
button on the Main Toolbar. The "immediate" form, shown first,
opens when an image or image set is displayed in the top-most
window. The general form can be used to select source images from
folders, windows, or by matching templates.
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Set Arcsecond Scale Properties |
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Profile [|>] |
Selects the parameter profile for this command and allows you to save or work with existing presets. |
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[Select] |
Opens the Select Source Images dialog to choose images from an image window, folder, files, name template, or a Mira File List. |
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Scale |
Enter the value in arcseconds per pixel. |
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[Calculate] |
Click this button to calculate the scale. |
This command applies a World Coordinate System ("WCS") calibration to the image or image set. This calibration replaces any existing WCS. However, this command creates an Undo copy so that you can use the Edit > Undo (Ctrl+Z) command to restore the previous coordinate system. To save the arcsecond calibration, save the image in the normal way.
To apply a linear arcsecond scale to an image or image set,
Enter the image scale value into the Scale field or click [Calculate] to have Mira calculate and insert it for you.
Click [OK] to set the image scale as a WCS calibration for the image or image set.
When you click [Calculate] in step 1, Mira calls the Calculate Image Scale command.
If the value to enter for the image scale is not known, you can have Mira calculate it or you can calculate it manually. To calculate the image scale, you must know the pixel size and focal length of the telescope used to create the current image. Use these in the formula below:
S = 206.265 P / F
where
S is the scale in arcseconds per pixel,
P is the pixel size in microns,
F is the focal length in mm.
Insert the value of S into the Scale field in the Set Arcsecond Scale dialog.
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