Split achromatic doublet problem and lens element centering in a drop-in barrel

A split doublet is more sensitive to aberration because the inner surfaces are typically strong in curvature and can independently misalign. To improve the centering of a lens element, we discuss using a strip of material inserted in the gap between the lens edge and the barrel. This technique has the benefit of relaxing the barrel inner diameter tolerance. Four examples are provided where lens centering was estimated to range between 0.025 and 0.050 mm.