With each photostencil material, there are guidelines for exposure times using various lamp types. However, these times are guidelines, and it is up to the operator to determine optimum exposure under his own conditions. 

The exposure calculator is a film positive comprising of five columns, each with a resolution target, a set of halftone tints and lines of text. Each column is backed with a grey neutral filter of different density. This concept enables five different exposures to be made simultaneously. 

Incorrect exposure is one of the most frequent causes of stencil failure. The Exposure Calculator provides quick, accurate determination of exposure times with all photostencil systems to alleviate this problem. It can also be used as a printing aid to optimize print quality, or as a means of process control. 

How to use the Autotype Exposure Calculator 

1. Estimate the correct exposure time using the guidelines available for all photostencil materials, then DOUBLE it. 

2. Expose the photostencil to the Exposure Calculator in the normal way, washout and dry thoroughly (Note: For indirect films dry the film unmounted). 

3. Examine the stencil to determine the correct exposure time. Interpretation of correct exposure depends on the stencil system. 

Reading the results of the exposure test 

The stencil will show variations in color from one factor to the next. Follow the color change from the lightest to the darkest until it stops. The factor where the color change stops is the column that represents optimum exposure. 

Once the correct factor has been chosen, multiply the factor by the test exposure time. This gives the correct exposure time (or number of units) for that particular stencil/mesh/light source combination. 

Example: 0.7 x 10 minutes = 7 minutes 

Correct factor x test exposure = Correct Exposure 

If there is still a color change between Factor 0.7 and Factor 1, this indicates an under-exposed stencil, DOUBLE the original test exposure, and repeat the test.