6.7.6 XFOCUS

OBST>XFOCUS 		<c_mode> /DEFAULT
		/NWAV_FCX <#> 
		/TIME_FC <Time(s)> 
		/STEP_FC <no_of_steps>

XFOCUS performs a series of on-source measurements where the vertical focus displacement (FCX) is stepped back and forth symmetrically about the hitherto best value. A parabola is fitted to the averaged values in order to determine the optimum focus. If parameters are entered as current values, they remain active until the verb is entered again, unless the /DEFAULT adverb is used to transfer the parameters into the default values.

• <c_mode> is the continuum observing mode (this is transferred to C_MODE),
  where T = Total-power and B = Beam-switched.

ADVERBS:

• NWAV_FCX Sets the number of wavelengths for focus travel during the measurement. <#> in [multiple wavelengths].

• TIME_FC Integration time in sec per ON-source measurement.
• STEP_FC Number of steps in each direction. If an even number is used, there will be no measurement at the best-guess value. A value of 3 measures at positions of -LENGTH/2, the best-guess position and +LENGTH/2, and back again.

EXAMPLES:

• OBST> XFOCUS
  This will do a XFOCUS using the default parameters.
• OBST> XFOCUS /NWAV_FCX 1 /TIM 15
  This will give 15 sec integration at -0.65 mm offset, 0 mm offset, +0.65 mm offset, +0.65 mm offset, 0 mm offset, and -0.65 mm offset for 230 GHz.