The Canon 55-250 EF-S lens
has a minimum focusing distance of 3.6 feet ... and at
full telephoto (400mm in 35mm format due to 1.6x focal length multiplier), that's some good magnification - 0.31x.
With help from my Son Kyle, lets see how close that is!
25% crop of complete image from Canon 40D - hand-held 1/250s, F/5.6, ISO1600
100% pixels from the center - depth of field is about 0.1" - note flash reflection