Finding the Right Exposure Time
Exposure times will vary depending on multiple factors. These factors include the amount of emulsion that is coated onto our screens, the age of our exposure bulb, as well as the mesh that we use. Lastly, the time will also depend upon the wattage of our unit. The key is to find the best time according to your particular shop.
To determine the best time to expose our screens, let’s use dual cure emulsion as a starting point. The following numbers are a guideline to give you an idea of where to begin your testing. However, an exposure calculator is your best bet to zero in on best time.
-Sunlight Exposure (30 Seconds)
-5,000 Watt Metal Halide (1 Minute)
-1,000 Watt Mercury Vapor (4 Minutes)
-Grow Lights (5 Minutes)
The definition of an exposure calculator is a film positive that comes printed with five or more identical images. These images include fine lines as well as dots. We expose the film onto a screen and wash out as normal. After the screen is washed out completely, hold it up to a light and compare the different images. The one that is exposed the best, where the image looks the most crisp, is our target. A formula under that image will tell us our ideal exposure time. Our actual exposure time multiplied by the number given under our ideal image will equal our best exposure time.
Best Target Number X Test Exposure Time = Correct Exposure Time
Another, less precise method, is the Step Wedge Test. We will write a future post about this method. Stay Tuned!