Lesson 2 of 4
What stays sharp
Aperture, focal length, sensor size and distance decide how much of the car is in focus. Watch the nose and tail drop out of the band.
Only one plane is ever truly in focus. Either side of it, detail blurs gradually, and at some point the blur becomes large enough that a viewer calls it soft. Depth of field is the distance between those two points, and it is decided by four things at once: how long the lens is, how wide the aperture is, how big the sensor is, and how far away you are standing.
The diagram samples five places on the car. Each one is drawn at the sharpness the optics give it, so you can see which end fell out of the band rather than reading a number and imagining it.
The five sampled points sit at genuinely different distances from the lens because the camera is off to one side. A point outside the band is drawn grey and blurred by the amount it misses by.
The 35 mm film frame. Every "equivalent" number is measured against this.
- Only 74% of the subject's length fits across the frame from here. Shorten the lens or step back to get all of it.
- Sharp from
- 7.66 m to 8.37 m
- Total depth
- 0.71 m
- Hyperfocal
- 179.0 m
- Diffraction limit
- f/21.5
- Crop factor
- 1.00x
- Circle of confusion
- 0.0288 mm
Presets
Where the sharp band actually is
The band is not a slab across the scene. It is a shell at a constant distance from the lens, which is why the plan panel draws it as an arc. Point the camera at a car from straight ahead and every part of it is at nearly the same distance, so almost anything keeps it all sharp. Move round to a three-quarter and the nose and the tail separate by three metres or more, and the same aperture no longer covers both.
Hyperfocal distance
Focus at the hyperfocal distance and the far limit stops being a number: everything from half that distance to the horizon falls inside the band. That is what the readout means when it says the depth is infinite. It is the reason a phone can leave focus alone almost all the time — its lens is a few millimetres long, so its hyperfocal distance is a couple of metres and nearly the entire world sits inside it.
Why stopping down eventually stops helping
A small aperture is a small hole, and light bends around the edge of a small hole. The resulting Airy disc grows in direct proportion to the f-number, and once it is wider than the sensor's own tolerance for blur, stopping down further trades sharpness everywhere for depth you may not need. The warning under the aperture slider fires at the f-number where those two cross. It is sensor-dependent, and dramatically so: a phone sensor is limited before f/5, a full-frame sensor not until about f/22, and a medium-format back later still. The physics of the light is identical in all three. What changes is how much blur the sensor can hide.
A note on the circle of confusion
Every number here rests on a choice about how much blur counts as sharp. The convention used is the sensor diagonal divided by 1500, which is what most published depth-of-field tables assume. It encodes a print size and a viewing distance. Someone inspecting your photograph at full magnification on a large display is applying a stricter standard, and for them every band on this page is narrower than it says.