Abstract

The advantage of objective over visual assessment of Cobb-type resolution test films is discussed. Experiments are described in which an existing microphotometer was used to establish the necessary objective resolution criteria. Following a suggestion in a recent paper by Fellgett, the density fluctuations due to film grain are reduced to a minimum by using a microphotometer slit of the same dimensions as the image of the Cobb bar falling on the slit.

The simple objective resolution criteria established are in terms of the contrast between the bars and intervening space of the Cobb unit. The numerical values of the criteria may vary with the type of film used the conditions of the resolution test. Values are given for the particular film and test conditions used in and the experiment.

The objective resolution criteria are applied to measurements on a resolution test film, and the resultant objective assessment shows good agreement with the visual “half-Cobb” method assessement.

It is suggested that the method could be applied generally and an automatic instrument for the objective assessment of resolution test films devised.

© 1955 Optical Society of America

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