Here is some more info I recieved about the Luminars:
(Info. credit; Spike Walker UK) ;

Zeiss Luminar macro-anastigmat lens magnification ranges;

16mm / f2.5 (x10 - x40) (optimal mag x16) RMS
25mm / f3.5 (x6.3 - x25) (optimal mag x10) RMS
40mm / f4.5 (x4 - x16) (optimal mag x5) RMS
63mm / f4.5 (x2 - x10) (optimal mag x3.2) RMS
100mm / f6.3 (x0.8 - x8) (optimal mag x2) M44 X 0.75mm screw
'zoom' Luminar which yields magnifications of x2.5 - x5

( ) means magnification range with good performance,

The Carl Zeiss Luminar macro lenses were designed for high magnifications
with image coverage up to the 4x5 large format and are renowned for their
resolving power and flatness of field.
Originally designed for use with the Zeiss Ultraphot photo-microscope they
can equally be used to great effect with macro bellows or tubes plus the
appropriate adapter.

Luminar macro-anastigmats are used without eyepieces and are justly renowned for their resolving power and flatness of field. They are available in 16, 25 40, 63 and 100mm focal lengths, the first four having RMS objective threads, the last bearing an M44 X 0.75mm screw and/or an annular dovetail for fitting directly onto a Luminar Head. In addition, there is the remarkable 'zoom' Luminar which yields magnifications of 2.5 - 5 on the microscope's 5 X 4 camera. This is also fitted with the Zeiss 43.5mm annular dovetail. The 16, 25 and 40mm lenses are attached to the Luminar Head by the 'egg-cup' adapter shown in the upper photograph. The 63mm needs a different one. For transillumination, the 16 - 100mm Luminars are used in combination with matching 'spectacle lens' condensers and a standard stage, but the 'zoom' lens needs the massive Macro Stage with its built-in condenser.