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All right, the power's now turned on to the heads and as you can hear there is noise from the fans. Those cooling fans serve to keep the heads from overheating as we do multiple discharges. I'm connected to my flash meter so we're, we're tethered in and we're set to do Oncor metering. What I need to do now is a series of tests across the product to determine the amount of fall off I'm getting from my light source, but I want to test only one light at a time.
And I cannot disconnect one light to meter the other, because the number of lights connected in the circuit directly affects how much power comes to each light. So I have to do this while both are connected. So what I'm going to do, this button right here, is what discharges the flash and gen, generates a reading. So I'm going to point this directly toward the strobe unit. Shield it from the fill, so I'm directing it towards the main. Press the button to fire the flash. And I get a reading of f11 and eight-tenths.
I'm going to go to the center of the garment, repeat the process. I get f11 and a half. And then I'm going to go to this end of the garment and repeat the process, and I'm getting f11. So I'm getting a falloff of almost a full stop as I go across here. To check the fill, we'll do the same thing in reverse. I've got f5.6 and nine-tenths. f5.6 and seven-tenths and f5.6 and a half.
I'm happy with that. That stays real consistent all the way across the board, but the falloff from my main is a little bit more than I want. We're almost getting a full stop of falloff, and that will be pretty dramatic. It's also a good example of the inverse-square law. If you look at the distance from the flash to the top of the garment, it's probably four feet. And the garment is almost three feet across. And what the law says, is that any time you double the flash to subject distance you decrease its intensity by a factor of four.
And what we're getting with the meter is bearing that out to a certain degree. But remember I said earlier we're going to try to cheat a little bit by using the arc of dispersion of the light source to make it more even. So, I'm going to take a second and I'm going to tilt that light up just a little bit. And that'll serve just rake it across a little bit more parallel and hopefully that curve of the arc will make the ratio work a little bit better as I go across. Then I'm just going to double check my metering again. We've got f11, f8 and seven-tenths, and f8 and six-tenths. So you can see we've compressed that from almost a full stop to only about four-tenths of a stop.
So we've got much better balanced light coming from our main, and it's also about two-thirds of a stop brighter than what we're getting from our fill. That ratio of two-thirds of a stop will make for a nice textural representation of the fabric. One other thing you need to remember is flash exposure is controlled strictly by aperture. We cannot control the intensity of the lights by shortening our shutter speed. All that we would accomplish if we went to a shorter shutter speed is risk the possibility of having the shutter partially closed while the strobes discharged.
So finally, now that we have ratios that I like, the last thing we need to do is take a reading for exposure where we don't block the lumisphere at all. Place it in the center of the product. Point it is directly towards the lens as you can. Make one last discharge and we get an exposure reading of f8 and eight-tenths. So that's where we'll set the camera. The camera won't do eight-tenths, will do just f8 and two-thirds. And so now we're ready to make our first test shot.
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