Canon EF 24-70mm f/4L IS USM Instructions Manual page 16

11. Image Stabilization during Close-up Shooting
For normal close-up shooting, the higher the
magnification, the faster the shutter speed must
be to prevent blur caused by camera shake.
Although it depends on the shooting conditions,
usually the shutter speed must be at least one
or two stops faster than normal.
The EF24-70mm f/4L IS USM is installed with
an Image Stabilizer that gives the equivalent
effect of a shutter speed approximately 3 steps
faster when shooting at a magnification of
0.5x, and approximately 2.5 steps faster when
shooting at 0.7x.*
* Depending on shooting conditions.
The magnification refers to the ratio between the
subject's size and the corresponding image size on
the focal plane.
ENG-15