The distribution of light in elementary optical images

The paper presents the results of a series of calculations on the distribution of light near the "star focus" of a centered lens system in the following cases: Freedom from aberration. Primary spherical aberration. Zonal spherical aberration. In the two latter cases the condition chosen is that when the least residual phase differences amount to π/2. The characteristic extra-focal effects are determined, and the effect of primary spherical aberration on resolving power is discussed. In the case of zonal aberration the greatest axial intensity is not found at the focus giving least phase residuals. In both cases of aberration a concentration closely resembling in some respects the "Airy" disc characteristic of zero aberration is found. These results are an extension of those previously obtained by Conrady and Buxton.