Working at Minimum Focus Distance: EF 100mm f/2.8L Macro IS
The EF 100mm f/2.8L Macro IS USM focuses to 1:1 — life size. At minimum focus distance, the working distance between the front element and the subject is approximately 14 centimeters. You are very close. The depth of field at 1:1 and f/2.8 is measured in millimeters. Almost nothing is in focus. This is not a problem to solve. It is the medium to work in.
Most photographers who own this lens use it between 1:4 and 1:2 — close enough to feel macro, far enough to maintain a usable depth of field. That is the practical mode. What gets underused is true 1:1, where the image plane and the subject plane are locked in an almost adversarial relationship.
At 1:1 and f/8 — which is where most macro shooters retreat for depth — you still have less than two millimeters of sharp field. Stopping down to f/16 gains you perhaps three or four millimeters, but diffraction begins to soften the image. The answer is not more aperture. It is more precise positioning, better light, and accepting a narrower intention for the frame.
The Hybrid IS in this lens handles linear camera shake — the small lateral and axial micro-movements that dominate at close range. What it cannot handle is subject movement. A flower in wind, an insect breathing, even the subject expanding slightly in the warmth of your lens hood shadow — all of these blow the focus plane. Shoot in burst mode, not to spray frames, but to increase the odds that one frame caught the subject at rest.
The technique discipline is working the camera position rather than the focus ring. Once focus is set to 1:1, move the entire camera forward and backward to land focus precisely where you want it. The focus ring becomes a fine adjustment. Your body movement is the main control.
At this distance, everything you know about depth of field becomes approximate. That uncertainty is where macro images are made.