 BetterPhoto Member |
Depth of Field Could you explain WHY aperture relates to depth of field? I understand that with a smaller opening, the depth of field is enhanced, but WHY does this happen? I don't understand technically how allowing less light in provides you with sharper depth of field. Thank you so much, I look forward to your response.
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Michael Christopher |
This is a very good question, and kind of complex one. I'm going to give it my best shot. When focusing on a subject their is only one plane or point which is in focus(plane of critical focus). Everything that is within the depth of field appears to be sharp but truly only one plane is actually in focus. This plane is represented as points on the film and everything thing else is represented by small blurred disc(circles of confusion). As the aperture is made smaller then the circles of confusion become smaller which makes them appear more like points and hence more in focus. Hope this helps.
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John A. Lind |
Yes, Michael is right. A little more info about what happens when you stop down: If a point is not at the "critical focus distance" from the camera, the farther from the lens axis (center of lens) a light ray from it travels through the lens, the farther away it will land on the film compared to a ray traveling along the lens axis. This is what creates the "circle of confusion" out of a point not at the critical focus distance. As you make the aperture diameter smaller (a larger f-stop number), the aperture diaphragm blocks out possible "ray paths" of light from traveling through and near the edge of the lens elements. The more you stop down, the closer a ray path must be to the lens axis to keep from being blocked by the aperture diaphragm. This is why the "circles of confusion" get smaller as you stop the lens down.
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