Collimation techniques for the Hubble Space Telescope before and after the 1993 December servicing mission are discussed. As a first step we convert actuator positions of the HST secondary mirror into tilts and decenters, by means of a conversion matrix. Theoretical estimates of wavefront errors introduced by known amounts of tilts and decenters are related to each other by means of a conversion matrix. Several sets of stellar images taken with the Faint Object Camera over a two year period are analyzed and aberration coefficients derived. A residual coma of approximately 1/19th wave at 632.8 nm is found in the images. We report here the secondary mirror move made, after the refurbishment mission in 1993 December, to remove the coma and the analysis of the images taken after the move to verify the collimation.