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Even with today's automatic flash systems, there are good reasons to understand how flash exposure really works. Brent details these concepts in this course. The course describes how to calculate the true power of your flash and how to modify its output to match your needs, a technique that can extend battery life, reduce recycle time, and provide exposure control that is more predictable than fully automatic modes. The course concludes with several shooting scenarios during which Brent explores the creative use of gels, reflectors, and other light modifiers.
- Understanding exposure basics
- Reviewing aperture, ISO, and shutter speed
- Adjusting strobe power and flash to subject distance
- Finding the guide number of a strobe
- Making calculations based on ISO
- Understanding power ratios
Skill Level Advanced
Okay, so now we're playing. Just keep that kind of a distant look because I think that's really working. So, in the last movie we established exposure on the background and on our model. I'm shooting at f/5.6, and that decision is what drove my flash to subject distances and my Power Ratio settings on the flash. So I am happy with my exposure on the subject at this point. She is normally exposed, and I've got nice colors on the background.
So, now we're going to modify the key light to soften it and really start creating pictures. Okay, the last thing we're going to do I think on this setup is we'll pull the diffusion flat in, and we're going to light her softly through the diffusion flash, because what I want to do is get her evenly illuminated from top to bottom. All right, I am going to kick the power of those two background lights down even further and then when we put the diffusion flat up, we will have a little less contamination from this light, so we're going to knock this down another stop.
Lauren: One more stop. Okay. Off camera here, it goes from 8 to 16. Brent: Yep. Lauren: That will be in the 11. Brent: That's fine. Lauren: Okay. Brent: Yeah, on the Power Ratio, that's fine. Lauren: Okay. Brent: So that's a one stop. Lauren: Got it. Brent: The power ratios go one to one, one-half, quarter, 8/16, 32. Go back to probably a quarter. Lauren: Okay, Brent: In this series, let's really animate, and you can give me lots of movement, and I'll just--we're going to have to pause three or four, five beats in between, but let's get a whole big series.
So this is where you want to be able to shoot fast because the model has only got so much energy and being able to hit every single one of these poses is really the idea. Nice, so here's what the setup, if you want to take a look. So this is actually what was going on, so we're getting fill, we've got the light, and there is the end result, there are some really nice shots in this series. So Lauren, I think on this series of shots, we want to start with the high key image, I am going to blow out both Savannah and the background by about a stop, and then I am going to bring it back to normal, simply by using ISO.
Lauren: Oh, good, okay. Brent: And while we're doing that, if you want to hit her with the fan, we'll get some hair move. Lauren: Okay, cool, yeah. Brent: After we've gone through that series, I'll go back up to ISO 400, and we'll change the exposure on the key light only, because what I want to do is reduce the overall exposure on her so that she stands out against that kind of blown-out background. Lauren: Okay, so, all right. Brent: So, Savannah, we are ready. It's getting cold in here so when we turn the fan on, it's going to be really cold on her, so we'll try to be quick.
For the set of images where I began by deliberately overexposing her, what I did was I backed up, I put a long lens on my camera, and I asked her to come towards me with a view towards shooting pretty wide-open and softening the background. So that's the change that we made for round two in this set of images. Okay, so you can see we've got blown highlights in the background, we've got hot skin tones, and it's a different look than what we've gotten before, and I like it, but we're going to start with this then we are going to go back down to a normal exposure simply by adjusting our ISO.
So Lauren, if you want to get the fan going. Lauren: Okay, Brent: And then, Savannah, just play to the camera and then a little bit to the light. Maybe put your head down and then kind of throw it back, sweet! Just hang out for a second, I am going to change the exposure, I am going to reduce the ISO by a-third, fire off another series, okay, nice! Then turn your body towards the diffusion flat and eyes at me, that worked, okay.
So I am going to go down another third to 250, let's go without the fan. Lauren: Okay. Brent: Okay, nice. Okay, one more time. Now I am going to reduce the ISO one more time, and then we're going to make this switch with the key light after a couple here. And then give me that long far-away look. So I decided to bracket my exposures two different ways.
I did that simply by changing my ISO, and it was only a one-stop bracket, and I did that for illustrative purposes and to get a little more visual variety. And then the second bracket that I did was by changing the Intensity or the Power Ratio on the key light, so I kept the background exposure the same throughout that series, but I reduced the intensity of the light from the key light by one stop, and that was simply to get some visual variety. So I am going to take the ISO back up to 400.
Lauren, why don't you drop that in third-stop increments so we can illustrate what happens. Lauren: Okay. Brent: With the key light, so it's one-eighth right now. So, you're going to go to 1/8th minus 3. Lauren: Okay. Brent: Minus three-tenths, rather. Lauren: Right. Brent: And I am taking the ISO back up to 400. Lauren: Okay. Brent: Okay? Nice. Okay, let's knock that key light down by another third.
So with this set of exposures, maybe you can give me a couple of spins again. Lauren: Minus 0.7? Brent: Yep, nice. Okay, Lauren, let's kick that light down. Lauren: Okay. Brent: Now the way that we have this set up, we're getting a little bit of rim light from both the background lights on her, the cutter card, it's just keeping you off the background, but it's spilling onto her, so we're starting to see as we've knocked that key light down a little bit of blue on. Lauren: Oh I see.
Brent: On her front side, and a little bit of red on her arms, so. Lauren: So this is-- Brent: the reason that we're getting that spill on her at this point that we didn't get at the beginning is because I asked her to move forward, and we didn't change the position of those cutter cards, so the light is now spilling onto her, but it's kind of a cool effect that we've created by happy accident, but what's important to note is the effect that changes as the intensity of the key light changes. So as I knocked the key light down, you'll see more of the blue and the red on either side of her.
So we're down a full stop from where we started. Lauren: Right. Brent: I'd say that's a wrap on this setup. So the first shoot is all over. Now let's take a look at some of the really wonderful images that came out of this. And when I first started shooting, I never would have believed that results like this would have been possible without using TTL or a Strobe Meter. But I've discovered over the course of my career that guide number math and the knowledge that comes from learning that really helps problem solve, and what that allows me to do is concentrate my energies on making good pictures rather than just getting good exposures.
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