6d button at the bottom right of the lens.

When the camera is in focus, the aperture of the lens is fully open. Even if you set a smaller aperture, the aperture will not change until you press the shutter. At this time, if you want to get an accurate depth of field value, just press the preview button of depth of field mentioned above, and then the camera will automatically reduce the aperture to the aperture set at that time, which means that the viewfinder of the camera will darken, and then you will get the depth of field corresponding to the aperture you set.