Specify how the focus distance changes with elevation at a given temperature.

Mandatory Arguments:

FocusCurveId id

The identifier of this curve, which must be an integer between 0 and 19. When the focus command is invoked, if the current temperature is covered by the temperature ranges of more than one focus curve, then the one with the highest numbered identifier is used.

Double tmin

The minimum temperature covered by this curve (C).

Double tmax

The maximum temperature covered by this curve (C).

Double f0...f90

The optimal focus distance, in millimeters, specified every 10 degrees from 0 to 90 degrees elevation.

Example:

The following example specifies two focus curves, one that should be used for temperatures between 9 and 20C, and another that should be used for tempertures between 19 and 30C. Note that the temperature ranges of the two curves overlap between 19 and 20C. For temperatures in this overlap range, the second curve would be used, because it has the highest numbered identifier of the two curves.

focus_tcurve 0, 9, 20, -29.87, -24.73, -20.33, -16.68, -13.76, -11.59, -10.15, -9.46, -9.51
focus_tcurve 1, 19, 30, -30.91, -25.84, -21.44, -17.79, -14.87, -12.61, -11.26, -10.57, -10.62

Context:

Unlike the focus_curve command, which specifies a focus curve that is independent of the ambient temperature, the focus_tcurve command can be used to specify how the focus distance varies with elevation over a given temperature range. This is useful at higher frequencies, such as at Ka band, where temperature effects on the focus become significant.

Up to 20 distinct focus curves may be specified, one at a time, with this command, identified by their id numbers. When the focus command is subsequently invoked, it looks for a curve whose temperature range covers the current temperature range, starting from the curve with the highest numbered identifier, and working back to that with the lowest numbered identifier. It uses the first compatible curve that it finds. If no curve is found that covers the current temperature, then it uses the default focus curve specified by the focus_curve command.

Note that if the specified value of tmax is less than or equal to tmin, then the focus curve associated with the specified id is erased. This can be used to erase temporarily installed focus curves.