Ready to watch this entire course?
Become a member and get unlimited access to the entire skills library of over 4,900 courses, including more Photography and personalized recommendations.Start Your Free Trial Now
- View Offline
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
So, we're going into the warehouse, and we've set up three different shoots inside a very small space, and the first one that we're going to take a look at is utilizing some industrial ductwork that we've found in the building, and we are going to illustrate using some different colored lights on the background to modify that background, and we're also going to shake it up a little bit by shooting with two different focal lengths on the camera to give us a wide portrait and then something that's a little bit tighter with a shallower depth of field. So, here we go. All right, so we've got this kind of high-tech background that we set up and what we're going to do here is put a red gel on one of the background lights and a blue on the other.
And we're going to let them cross in the middle and give us a nice magenta high-tech, and then we'll put a neutral light on you, probably somewhere maybe right around here to get started. And then we're going to drop a couple of lights into these tubes that kind of create some accents on the background. We're going to start with hard lights, so on modified, and when we're done with that we'll leave the background lights in place, move further away and get some tighter portrait shots and kind of play around with the depth of field to shake up the background focus.
So, you can take a break for 5 minutes, we'll get the lights set and off we go. So, I decided to shoot at f/5.6 for two reasons. The first was to allow me to get the background lights pretty far away from the set, because I wanted to evenly illuminate the background, and to do that, it's really helpful if you get the lights far away. And the other thing is I wanted to use a relatively shallow depth of field on this initial shot. So, 5.6 served two purposes.
Let's set a red light on this side, blue on that, let's measure off. We're going to shoot at 400. So, let's set this light 18 feet away, right? Lauren: Okay. Brent: And then we're going to set at a quarter power. Lauren: Got it. Brent: Because I did the calculation, ISO 100, we are shooting at 400, so we'll back it down to quarter. So, I've got Lauren set up 18 feet away from my background. A quarter power which would give me normal exposure but what I've done is I had him put a blue gel on that flash, and I need to compensate for that so what I had them do is bump the power up by stopping a third in order to make up for the density of that gel.
So, I think I told you a quarter power, so we need to compensate for that. So, why don't you go to minus two-thirds of a stop? Lauren: Okay. Brent: So, you'll go to half and then plus the third. Lauren: Okay. Brent: So that should get us a good start. Lauren: Yeah. Brent: I'm going to have Lauren kind of feather that light or cheat it across the face of the background so that it is aimed a little bit beyond the midpoint, and that will help more evenly distribute the light across the width of the background.
So, I'm going with a red gel on the left- hand side, and the reason that we're doing that is to create kind of magenta where those two lights cross. So, we'll see red, we'll see blue, and we'll see the complementary magenta color in the middle. And again, I'm compensating on the red gelled light just as we did on the other side but this time I'm using a two stop conversion or compensation because that gel is a little bit denser. Okay, so we'll just walk through the math.
If we're at ISO 100, guide number is 90, I'm shooting at 5.6 so we said that put the flash, was it 16 feet away? Lauren: 16, 18. Brent: 18 feet away. So we're going to start at 18. I'm going to dial it down to a quarter power because I'm shooting at 400, and then we're going to take it back to full power because of that filter, or the gel rather. Lauren: Cool. Okay, we'll do that. Brent: All right. We also had these really cool elbows in this set, and what I did was stuck a flash in a couple of those and played off of the yellow insulation that was in there.
So, I've got yellow highlights coming out of these, and I just set the exposure for those flashes by guessing at the beginning. I ended up having to make some adjustments to that, but I just went off of instinct on my initial power settings on those. I chose to put the lights at a pretty severe angle to the background for a couple of reasons. The first was to take advantage of the kind of the depth that we created with those vertical tubes. We offset them a little bit and by getting that light pretty far off to the side we were able to create some shadows.
The other thing that I wanted to do is to really keep the light from spilling on to the model, and I was--it's a little bit easier to flag her off by virtue of having those lights pretty far around to the back side. So I think we're off to a good start if we can keep that colored light off of her. The very first shots that I did were with the little accent lights in these elbow bends, and so when I put those in place and didn't have the other two lights going on, I got a really nice saturated color coming off from them, but by virtue of then adding the two background lights that kind of got diluted, so I needed to revise that a little bit.
After about 10 minutes' time, we got the background lights set pretty much the way that we wanted them. So, then it was time to start working on the key light on the model herself. All right, so if you can just hold your arms out like that because I want to see how we did with two flags. One of the things when you're using multiple lights is really being aware of how those lights interact with one another or overlap, and oftentimes you don't want them to. And certainly in this case, in the initial set up we didn't want that.
So it's important to test before you get too far along to see if indeed you are contaminating your main subject with these two lights, and indeed, even though we did have her flagged off, we saw a little bit spilling on to her body when she was in position. So, the way that I corrected for that was simply to have her take a step forward, and that's all it took to fix the problem. Why don't you come forward just one step, hold the same, hurry out, there we go.
Okay so that's going to be your mark, so you did a really nice job flagging those off because we're not getting any real spill off of either those two lights. Lauren: Right. Brent: So now what I want to do with the key is get it pretty close to her so that the light fall-off doesn't contaminate the background. So, let's get that. Let's start, I'm shooting at 5.6, let's get that light maybe 8 feet from her. The guide number on my key light is 90.
I decide to place the flash 8 feet from the model, with a view towards minimizing the amount of light that was going to spill on to the background. So, if I divide 8 feet into my guide number of 90, that gives me a shooting aperture of f/11. But remember, I'm shooting at 5.6, so I need to cut the power of that strobe by two stops from full power to half power to quarter power. It's further complicated by the fact that I'm shooting not at ISO 100 but at ISO 400.
So I need to reduce the power ratio two more stops from quarter power to 8th power to 16th power. So, we should be getting some nice accent from that, the strobe that's in the can. So, you can just relax. We'll do a little test. I took the first exposure at 8 feet, and I did get a little bit of fill on the background, it did indeed illuminate it, and I want to minimize it as much as I can. So, I decided to move the flash in a further stop to f/5.6 which required that we cut the power ratio from 16th power to 32nd power.
Okay, so Lauren, what I tried to do with that move was to let this go a little bit darker again. So I want to--we're going to increase the exposure on her because that was a little bit underexposed by virtue of it being up high, even though the distance on the floor was right. So that should, it's going to open her up a little bit, and by moving it a little closer that's going to knock that down. Okay, so before we get started I will have you look in the direction of the light just to see how that looks and so you can look over, there you go.
So, you can see we got an awful lot done in about 12 or 15 minutes. We did it without benefit of TTL, we did it without using a strobe meter. Simply by applying guide number math and filter factors for the filters that we used or the gels more properly, we were able to achieve proper exposure very quickly. In addition, we compensated for colored gels on those background flashes, and we got proper exposure on our model. Now, in the next movie you're going to see is modify that key light to really get some wonderful images.