A study has been made of the printed images from a projection printer whose light source can be varied to provide illumination of various levels of partial coherence. The coherence interval for five light source configurations was measured with a shearing interferometer at the object plane of the printer. Many test images were made with the printer for each of the five degrees of partial coherence and results showing image quality as a function of coherence interval have been reported. It was found that with an 11µm coherence interval the image forming characteristics were typical of an incoherent instrument and could be adequately explained by a linear transfer function. An increasing departure from linearity was seen as the coherence interval increased to 71µm. This could be best seen as an increase in ringing around edge images and emphasized high frequencies in sine wave images. For coherence intervals greater than 71µm few changes occurred in the image microstructure indicating that the printing characteristics are essentially those of a coherent system. Tri-bar resolving power showed a factor of two drop from the incoherent to the coherent imaging condition. Image microstructure effecting the macro tone reproduction was observed and concluded to be an example of the half tone effect.
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Department, Program, or Center
School of Photographic Arts and Sciences (CIAS)
Radl, Bruce, "Image Quality Dependence on Partial Coherence in a Projection Printer" (1979). Thesis. Rochester Institute of Technology. Accessed from
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