Alignment of schlieren and Rayleigh optical systems in the ultracentrifuge

Difference sedimentation equilibrium technique for measuring small changes in molecular weight. I. Theory and computer simulation

“…In evaluating potential errors we must first consider limitations of the ultracentrifuge optical systems. Although it has been calculated by Richards et al (1972) that current optical systems are capable of resolving gradients as high as 500 fringes/cm, there may be another limitation imposed by the physical dimensions of components in the system. This occurs because the axial deviation of the light is proportional to the refractive index gradient so that at large values of dc/dr the deviation is sufficiently great to cause the light to strike a nontransparent component, such as the optical tube or a lens mount.…”

A difference sedimentation equilibrium technique for measuring small changes in molecular weight. II. Experimental

“…To reduce this inaccuracy to a negligible value the mask should be positioned within 10 n and 0.1°. Although it is possible to achieve sufficient accuracy with the general utility mask (Rosenthal, 1969;Richards et al, 1972), it is an extremely time-consuming and frustrating task. The mask described by Bowers and Haschemeyer (1969) affords some improvement as it permits external control of the rotational adjustment.…”

“…The mask described by Bowers and Haschemeyer (1969) affords some improvement as it permits external control of the rotational adjustment. The precision mask (Kirschner, 1971;Richards et al, 1972) is more easily aligned than either of the preceding since the adjustments have greater sensitivity and allow the translational positions to be reproduced with a fair degree of accuracy. The mask described here is even more advantageous because of the externally adjustable translational control, and the ease of reproducing, at will, any desired translational or rotational position with a high degree of accuracy.…”

“…If the slits in the mask are parallel this relation should be constant. However, it has been shown in velocity experiments that the fringe spacing and therefore the displacement increases with a lower mask (Kirschner, 1971;Richards et al, 1972) acreases with an upper mask (Richards and Schachman, 1959) in regions associated with a high-concentration gradient. It is important to consider this phenomenon in the analysis of the difference concentration distributions because the regions which are most useful for determining Act occur at high gradients.…”

“…The optical system was aligned according to the procedure of Richards et al (1971), with the camera lens focused at the two-thirds level in a cell assembled with sapphire windows. A precision Rayleigh mask (Kirschner and Richards et al, 1972) mounted on the lower lens was used for all but one experiment which will be described below. The mask was aligned to 10 u translationally and 0.2°r otationally by the procedure of Richards and Schachman (1959) with a modified wide single-sector centerpiece made by removing the dividing rib from a conventional double-sector centerpiece (Yphantis, 1960).…”