Bon, quelques liens plus bas, et une explication retrouvée dans plusieurs de ces liens :

Yes, there you have it. Except that somebody is undoubtedly expecting me to mention something about depth of field. So here you go: with equal framing at equal focal length and equal aperture, depth of field will decrease as sensor size increases. So you could say, depth of field is inversely proportional to sensor size—given all of the above variables remain, err, constant. Of course, if you say that, as I just did, you will probably confuse the heck out of everyone—including me. But yes, sensor size does affect depth of field, but in truth, it does so indirectly. The crop factor of a smaller sensor generally means you will be shooting with a shorter focal length lens or from a greater distance to your subject, and these two things directly increase depth of field. You could shoot with the same lens, at the same aperture, from the same distance, and get the same depth of field regardless of sensor size—but you would have completely different images from each sensor. The full frame picture might be a full-body portrait; an APS-C sensor would yield a three-quarters portrait; a 1″ sensor would give you a headshot; and a 1/2.5″ point-and-shoot sensor would produce a close-up of an eye. Or something like that. Oh, would you look at that? It’s five o’clock somewhere.

http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm
http://blog.prophotosupply.com/2013/full-frame-vs-aps-c-m43-and-what-crop-factor-actually-means/
http://www.bobatkins.com/photography/tutorials/crop_sensor_cameras_and_lenses.html

Merci à tous