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Although there has been previous research concerned with image size, brightness, and contrast in projection standards, the work has lacked careful conceptualization. In this study, size was measured in terms of the visual angle subtended by the material, brightness was stated in foot-lamberts, and contrast was defined as the ratio of the difference between the brightness of the background and the object to the brightness of the background. The effects of these independent variables were assessed by exposing three seventh graders (one boy and two girls) to all 125 experimental conditions in 20 half hour sessions. The subjects matched patterns on the upper half of a slide with one of two on the lower half. The criterion measures were reaction time and correctness of response. Brightness did not affect either of these criteria. However, reaction time tended to be shorter with an increase in visual angle and longer for minimal levels of contrast. Correct responses were largest for the middle value of visual angle and for higher levels of contrast. An inverse relationship between angle and contrast produced a maximum number of correct responses. Application of these results in the classroom is difficult in view of space and equipment limitations. (PM)