Teacher’s Pets

My third, and probably last, post from the Taking Control of Flash Photography course that I ran for the first time last Sunday week walks through about the only photograph I took that day that I knew, before I even got up that morning, not alone that I was going to take it, but how exactly I was going to light it.  It would be the last photo of the day, and would be a group shot of all those who had taken the course.  And I was going to light it exactly as I had lit group shots like it in the past – using a go-to lighting scheme that would be quick, even and hard.

Under a little bit of time pressure, but wanting to get the shot, I cheated the class a little bit on this one as I jumped straight to flash power that I knew, from previous experience with this type of shot, would work.  But in a way that’s the point – I was using a lighting scheme I’ve used before, in very similar circumstances (a medium-sized group in open shade), and my putting my lights where they were on that previous occasion, I knew what a good starting point would be for things like aperture, flash power and flash-to-subject distance.

To begin, as you almost always should begin when trying to lit a portrait where there’s some ambient light, I put my shutter speed straight to my max sync speed of 1/250s to see what sort of working aperture I’d be required to use to keep the ambient exposure under control.  If I was doing this step by step I’d have taken a straight shot at 1/250s at whatever aperture was set on the camera, and worked the aperture open or closed from there to get a decent background exposure.  In reality though I was able to get the ambient exposure tied down pretty quickly by setting an exposure compensation of -1.5 stops and using shutter-priority mode (a rare use of it, for me) to let the camera figure out that at 1/250s, ISO 200, an aperture of f/6.3 would underexpose the ambient scene by a stop and a half.

That gives me this:

Now I just want to add light using my small flashes, so that the subjects of the photo are properly exposed.  Ideally I’ll do so in a way which throws even light across the group – I don’t want some parts of the group to be more lit than others.

The key to achieving even lighting is twofold.

First I need to use hard light sources – not particularly for aesthetic reasons but because and modifier I would be inclined to use to soften the light is going to suck up a lot of power, and I need power, because I need to put those light sources a reasonable distance from the group.  Afterall, they need to be out of the frame, and no matter where I put them, they are going to be quite a number of feet from at least some members of the group.

Secondly, I need to feather the light sources so that the illumination from left to right is even.  Let’s look at this more closely.

Suppose I decide to put a light at camera left, at about 45 degrees to the group.  If I point that at the left-hand side of the group, I can probably get that side well lit, but the light is going to fall off across the group (as the distance from the light to the subjects increases).  OK, so I could add a light source at camera right too, and point that at the right-hand edge of the group.  I can get the light on both edges reasonably even, but the intensity of the light will vary towards the middle.  I could add a third light for the middle section of the group, but that would have to come from near the camera’s axis, and I’d need to control the spill from it to avoid the shot looking like it’s lit by three spot lights, and even still there’d probably be variability.

A better approach is to take that camera left light source, and point it across the front of the group, at the person at the far right.  Similarly with the camera right light source, point it across the front of the group, at the person at the far left.  The beams from the two light sources cross in the middle, but in front of the group, so most of the light falling on the group is from the edges of the beams.  The closer people to the light sources are lit more by the edges than the centres of the beams, and so it all pretty well evens out.  This is called feathering the light.

Building that up one at a time, I dial my camera right light to 1/4 power – I know from doing this setup before that at the distance I’m working with, 1/4 power will be close, and it proves to be very close – and I get this:

That’s just one light source, and the exposure of the faces is pretty even.  Let’s add in the camera-left light, also at 1/4 power, as we want a symmetry to the lighting that gives us that even illumination:

That looks pretty good, and much improved over the ambient exposure.  You might notice at the back of the group, one of the subjects – Pauric – looking behind him.  He’s actually checking if the third light, because I did decide to use a third light, is firing.  The reason I added the light there was to try to add some separation between the group and the background, and reckoned it would create some nice rim light at the centre of the group at least.

The light wasn’t firing in the previous two shots (as I hadn’t set the power for that channel on my camera) but it does fire in the final shot up top, repeated here again:

Because everyone on the course is in this photo no one was able to take a setup shot, though the afore-mentioned Pauric sent me this setup diagram he created afterwards.  You can see that the SB-800 backlighting the group is at 1/8th power.  I didn’t dwell too much on that flash power setting at the time because, with the role that light was playing, there’d have been some leeway in what power setting it could have.  More important was the flash power of the two SB-600s, and as you can see from the diagram, how they are directed is key to achieving even lighting also.

Setup diagram by Pauric McGroder