An apparatus for measuring an optical property of a sample, comprising: a source of optical energy; an optical detector; a first window arranged to receive radiation from the source of optical energy over free space; and a second window which is in optical communication with the optical detector, so that a sample disposed between the pair of windows (5', 5) may be optically interrogated using the optical detector; wherein the first window and the second window are both moveable with respect to the positioning of the source of optical energy, and wherein the surfaces of the first window and the surfaces of the second window are further configured to respectively provide a first optical wedge and a second optical wedge so as to minimize channel spectra; an adjustable mechanism for controlling a separation betweenf the first window and the second window at a variable distance, to adjust an optical path length, in order to pull the disposed sample into a column contained by surface tension or to squeeze the sample during optical analysis; and a processor adapted to control the adjustable mechanism and additionally operable to automatically collect and store optical information from interrogated sample(s) that have been pulled and/or squeezed to various different optical path lengths; wherein either the first window is configured with a pair of flat surfaces angled with respect to each other to provide the first optical wedge and the second window is configured with a flat surface and an off-center conic surface to provide the second optical wedge; or the first window and the second window are each configured with a flat surface and an off-center conic surface to respectively provide the first optical wedge and the second optical wedge. a source of optical energy; an optical detector; a first window arranged to receive radiation from the source of optical energy over free space; and a second window which is in optical communication with the optical detector, so that a sample disposed between the pair of windows (5', 5) may be optically interrogated using the optical detector; wherein the first window and the second window are both moveable with respect to the positioning of the source of optical energy, and wherein the surfaces of the first window and the surfaces of the second window are further configured to respectively provide a first optical wedge and a second optical wedge so as to minimize channel spectra; an adjustable mechanism for controlling a separation betweenf the first window and the second window at a variable distance, to adjust an optical path length, in order to pull the disposed sample into a column contained by surface tension or to squeeze the sample during optical analysis; and a processor adapted to control the adjustable mechanism and additionally operable to automatically collect and store optical information from interrogated sample(s) that have been pulled and/or squeezed to various different optical path lengths; wherein either the first window is configured with a pair of flat surfaces angled with respect to each other to provide the first optical wedge and the second window is configured with a flat surface and an off-center conic surface to provide the second optical wedge; or the first window and the second window are each configured with a flat surface and an off-center conic surface to respectively provide the first optical wedge and the second optical wedge.