Depth of Field and Remote Speedlite Power Adjustment

When I was a young photographer shooting portraits in a studio we had setup a simple means of ensuring proper exposure at different apertures. It was a string attached to the reflector of each light. There were knots in the string for F5.6, F8.0 and F11. Grab the string at the appropriate knot and pull the string to the subject. Done. Now, theres a much easier approach and one doesn’t have to move the lights.

One advantage the newer speedlites and strobes offer is remote power adjustment. The obvious benefit is not having to walk from the camera position to the light to change its power setting. Some systems offer an additional benefit; being able, once the lighting scheme is setup the way one wants it, to adjust power on all the lights being used while keeping the relative power setting constant.

Here’s an example;

I set up the scheme I wanted for this headshot with the 85mm lens at F2.0, ISO 100.

This demonstration was setup using Nissin Air Commander System. It consists of Di700a speedlites and an Air Commander trigger/controller that fits in the camera hotshoe. I used M mode for this demonstration. The system supports ETTL, including High Speed Sync.

There are three lights, the main, camera left, was set to 1/32 power. The fill, right over the lens, was at 1/64 power. The background, shooting through a white diffusion disk, was also at 1/64th power.

The commander can control each of the three groups or all the groups together. Its simply a matter of pressing the set button. When the A, B or C group indicator is flashing then turning the control wheel changes power for all lights assigned to that group. When all three groups are flashing turning the control wheel changes the power setting for all the groups.

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Now, to shoot at F2.8 all that is necessary is to make sure the Commander has all three groups flashing and then turn the control wheel to increase power 1 EV. And take the shot.

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Since Depth of Field expands in both directions from the focus point. Increasing the F number brings more and more of the subject’s head into focus. Generally, the focus point for a headshot is one of the eyes. I use the eye closest to the camera, of the eye closest to the main light if its a straight on shot. In these examples the glasses frame is the point of focus. For F2.0 to F2.8 the tip of the nose has become more in focus and the field of focus is working its way back toward the ear.

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At F4.0 all the front of the face is in the plane of focus and it has extended back to the sideburns. At five foot focus distance F4.0 delivers twice the depth of focus as F2.0 according to DoF Master website. These example images where shot at about that subject to camera distance.

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At F5.6 The ears and hair are coming into the Depth of Focus range as well. The back should is still out of focus. The depth of focus at F5.6 is about 4 inches at the 5 foot focus distance, evenly split in front and behind the point of focus. Using the eyes as the point of focus, since they are to focal point of a headshot, lets a photographer easily determine how much of the face will be in the depth of focus range. Its nice to have the additional artistic control easily available from the camera position via remote power control for the lights.

I used the Nissin system with a Sony A7RII. The Canon 600EX-RT system has the same capabilities. And there are others. Some studio strobes also offer this capability. The one I’ve used is the Einsteins with a Cyber Commander, manufactured by Paul C. Buff Inc. There are probably others of which I’m not aware.

Several strobe and speedlite systems offer remote power control. Its the ability to change power over multiple groups while maintaining the lighting scheme that is critical for this approach to lighting.