The Stouffer 21-Step Transparent Guide is heralded around the world as "the platemaker's choice". It serves as a gauge to evaluate the variables encountered in the exposure and processing of lithographic plates and photographic materials by contact.
- Set your contact printer or vacuum frame to make several trial exposures on separate pieces of film, with each exposure for a different length of time.
- Make three exposures: one determined by past experience or the exposure normally used in daily production, one for less, and then one for more. It may be necessary repeat this testing procedure using different exposure times.
- Process the test negative for the time and temperature recommended by the film manufacturer. It is important to keep processing consistent.
- Examine the step tablet image on each of the negatives. Select as the best the negative in which step 7 (on a 21-step step tablet) is developed to a dense black, with step 8 only slightly dense. Step 7 will be the aim point for normal copy.
There are many different ways for exposing plates. There are an abundance of different exposure systems and processing techniques. The one constant is the step tablet. Use the step tablet as a benchmark for all exposures to achieve accuracy and repeatability.
To find the exposure factor to hold more or less steps on a Stouffer 21 step Platemaker Sensitivity guide follow the chart below.
|To Change Exposure||1 Step||2 Steps||3 Steps||4 Steps|
|To Increase Exposure||1.41x||2.00x||2.82x||4.00x|
|To Decrease Exposure||.71||.50||.35||.25|