On his last visit to Lawson in St. Louis, George Legh-Page from the Ulano Corporation, demonstrated an Exposure Calculation Test. This test, when used in conjunction with your own positives, will help you determine the proper exposure time for each of the mesh counts used in your shop. This reusable test should be used any time you change your emulsion, coating thickness, films, or exposure lamps. It will work with both inkjet film, and laser vellum. The Ulano Exposure Calculator is available to order from Lawson.
Hi, Im George Legh-Page with the Ulano Corporation. Im here at Lawson Screen & Digital Products in St. Louis. Today, I am going to show you the application for doing an exposure calculation. Ulano sells an exposure calculator which you will see is a five step filter to be used in conjunction with a piece capillary film, or even better yet use one of your own positives. Because those that are using laser film or vellum will get a more accurate reading by using your own set of film or type of positive versus the film that is not typically what you would expose. But as you see on this calculator here you have five steps. The clear area here is one hundred percent where there is no filter; its darker, scaling down. Youve got a seventy percent filter, fifty percent, thirty three percent, twenty five percent is the darkest filter area. So with one screen with your film, it allows you five different exposure times through these filters onto one screen. Most of you will do a screen it doesnt work; it doesnt work, until finally something works, but you never know what the next step would look like. So, ideally with your exposure calculator you are taking a time that is basically longer than presently what you are shooting. So, for example, if I was going to shoot this velum I would put the five step filter over my image area, and if Im presently at a five or six minute exposure rate with your light, (and these will work on any type of light source you may use) what you want to do is double up your time. By doubling up your time that means that your present time is going to fall in this mid-scale, fifty percent region. So if we go from five minutes to ten minutes, at the end of this we wash this out we’ve got ten minutes, seven minutes, five minutes, three and a half minutes and two minutes. So, it allows you to go from hopefully under exposed to over exposed, and thats the value of an exposure calculator. One screen with five different ranges of exposure times.
What we’ve just completed is exposing our exposure calculator and I am washing this out now. What we’ve done is made a total exposure of this at two minutes. As you will start to see with a 100% filter this is two minutes, seventy percent of two minutes, fifty percent (which would be a minute in this range), thirty three percent of two minutes and twenty five percent of two minutes. You will see in here the color outline is tinted which means you are not cross linking the entire emulsion all the way through. Up here at one hundred percent we are still able to maintain our bulls eye marks, or register marks, and there is no color outline changing here as well. If you look at it from the backside which was the furthest part to expose for the light, you will see in here how soft and slimy it is in the twenty five percent range. That’s telling you right there that you haven’t exposed all the emulsion that you put on. So you are obviously going to wash down the layers and you are going to have a thinner coat of emulsion, maybe causing more pin holes or early breakdowns. There is still some change in here, but it is a little harder on the thirty three percent filter. In the fifty percent it is even more solid, but looking at the color range and the resolution, our best exposure time is solid here at the seventy percent onto one hundred percent. So, between two minutes and seventy percent (a little less), maybe a minute and three quarters would be my best time. So thats the value of an exposure calculation; by using your film positive with five different time values: one hundred percent, seventy, fifty, thirty three, and twenty five. Any time you feel it slimy on the back side that is a symptom that you need to increase your time. So, if you invest in one, it is one of the best investments you will do because it is reusable whether you change the light source or change the products that you use. You can always go back and do your exposure calculation.