A `2D + λ' mode using two detector angles and wavelength is added to the modes of operation of a six-circle diffractometer, i.e. `4S + 2D' diffractometer [You (1999). J. Appl. Cryst. 32, 614–623]. In synchrotron sources, the X-ray energy, and hence the wavelength, can be a degree of freedom for angle calculations. For diffractometers with two detector circles, therefore, the variable X-ray energy can be the third degree of freedom, sufficient for accessing reciprocal space without rotating the sample. This mode is useful for limited sample rotations or X-ray beams focused smaller than the diffractometer circle of confusion.