Modulation transfer function of a finite scanning microdensitometer slit.
Inherent in the line-spread function approach in modulation transfer function (MTF) determinations is the use of a microdensitometer to scan the density pattern resulting from the line exposure. In such a procedure, loss of fidelity in the distribution being scanned is expected. This loss is due in part to the use of a finite-width scanning slit. In spite of the central role of the scanning slits in the MTF determination, little if anything has appeared in the literature from which one can quantitate the effect of a scanning slit on the MTF determination. This paper analyzes the loss of response attendant with use of scanning slits of differing widths. Specifically, the MTF of a finite scanning slit is derived. A method for correcting for loss of response, given a specific slit width, is indicated on the basis of the chain-multiplication property of MTFs. The current practice of using a 10-mum width for film-screen combinations is shown to be justified. Results can be generalized to any configuration scan slit. In addition, it may also be applied to any generalized sampling or display-type slit.
D003720:Densitometry / Q000295:instrumentation*; D008904:Miniaturization; D008962:Models, Theoretical