Invisible to the bare eyes, mist activating out door cam at night

Can any body help or has anybody else experienced thisthe last couple of nights my back garden outdoor cam has been activated by a mist / smoke wafting down in front of the camera this mist is not visible to the human eye but I can see it on live view on the iPad I've stood out there at 2am viewing my iPad but unable to see it with my bare eyes, I've turned on my existing outdoor light to help see what it might be but still nothing but visible on the iPad It's not my boiler exhaust which does activate it sometimes but not on at 2am the boiler is offI'm completely baffled has anybody else experienced this or do we have a ghost or ectoplasm or some other phenomena I'm not nuts honestly