Alignment of schlieren and Rayleigh optical systems in the ultracentrifuge. I. Focusing of the camera and cylindrical lenses.

Abstract Special efforts were devoted toward increasing the sensitivity and accuracy of focusing the camera and cylindrical lenses of the schlieren and interference optical systems of the ultracentrifuge. Through the use of appropriate masks containing double slots the sensitivity in focusing each of the lenses was enhanced considerably so that the lenses could be positioned properly to better than ±0.25 mm. In addition, much of the subjectivity in judging the correct focal position was eliminated. Equations were presented relating the physical and optical parameters of the various components of the system and tests were included which demonstrated the validity of the procedure. These equations permit the calculation of the correct position of the camera lens and the relevant magnification factor for any level in the ultracentrifuge cell such as the 2 3 position. This information is essential for accurate molecular weight determinations from high-speed sedimentation equilibrium experiments in which there are large concentration gradients near the bottom of the solution column.