Depth of field can make or break a portrait. It decides whether a viewer’s attention stays locked on a subject’s eyes or drifts into the blur of the background. Getting it wrong doesn’t just soften an image; it can shape how you compose and light every shot. Many people misunderstand what truly affects depth of field, and that misunderstanding can quietly steer years of work in the wrong direction.
Coming to you from John Gress, this revealing video walks through the real factors that control depth of field and how one long-standing belief about it turned out to be wrong. Gress admits he spent decades thinking focal length had a major influence on how much of a subject appeared sharp, only to find that it doesn’t play the role most assume. For portraits, focal length changes how the background looks, not how much of your subject stays in focus. Gress uses side-by-side tests to show that when the subject size stays the same in the frame, the depth of field barely changes, even if the lens does.
He traces the mistake to how most people first learn depth of field, as a formula tied tightly to focal length. That formula is correct on paper, but it leads to false assumptions in practice. A landscape at 35mm behaves differently from a close portrait at the same aperture. Gress proves that aperture and distance to subject are the true levers. A wider aperture like f/1.8 isolates a face beautifully, while stopping down to f/11 keeps props and details crisp when shooting in studio. He cautions against shooting wide open all the time just because you can.
The video goes deeper into how distance and sensor size alter the equation. Step back, and more stays sharp. Move closer, and your focus narrows fast, especially in macro work where f/11 still leaves paper-thin focus. He compares full frame and medium format sensors like the Fujifilm GFX 100S, explaining that you may need to adjust aperture by about a stop to get the same look. These are the kinds of subtle details that shift how you approach every session, from a tight headshot to a group portrait.
Gress also tackles common myths, including the “one-third in front, two-thirds behind” rule. It’s only sometimes true. At close distances, the split is closer to half and half, while at longer distances, most depth falls behind the focus point. He introduces the concept of hyperfocal distance—the point where everything from a few feet out to infinity looks sharp—and explains why modern autofocus lenses have made that trickier to calculate without an app. He finishes with diffraction, the softening that happens when you stop down too far. Lenses are usually sharpest around f/5.6 to f/8, but practical needs come first. For jewelry or product details, he notes that shooting at f/16 might serve better even if it’s not optically perfect. Check out the video above for the full rundown from Gress.
If you would like to continue learning about the art of portraiture, be sure to check out our range of tutorials on the subject in the Fstoppers store.
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