Both aperture AND relation of the subject to camera will determine DOF.
...AND focal length. Also, for the sake of completeness and hopefully not to confuse the issue, the fourth factor is the circle of confusion (CoC, which is related to sensor size, and somewhat arbitrarily defined for various sensor formats based on a specific print size and viewing distance).
So...if you hold the other listed factors constant, you get shallower DoF with:
- Wider aperture
- Closer focus (subject) distance
- Longer focal length
- Smaller circle of confusion
The last one confuses many people (pun intended), because CoC decreases with decreasing sensor size, i.e. DoF is actually shallower
with a smaller sensor. But remember - the above holds true when you change one factor only. So, if you keep everything but the body constant - same focal length, aperture, and distance, the 7D will give a shallower DoF than the 5DII (try it - plug any numbers you like into DoFMaster
, and change only the camera popup menu). Of course, your framing will be quite different. It's not just esoteric, though - it has real-world implications when doing an AFMA with a commercial tool (e.g. LensAlign), where you shoot at the same distance relative to focal length, independent of sensor format. In that setting, you can easily see the shallower DoF with the 7D (compared to the 5DII), and while the standard ruler is fine for 400mm f/5.6 on APS-C, the same lens on FF is marginal, and easier to calibrate with the longer ruler.