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. 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.
This command is opened from the View > Coordinates menu.
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. If you want 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.
Click [Apply] to set the image scale as a WCS calibration for the image or image set, or
To apply the value and close the dialog, click [OK] instead of [Apply].
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.