I took few night shots between 04.00 to almost 06.00 am with wide open aperture, so to be able to do hend held shooting. I have seen see the results as not good. It's ok as far as the picture are concern, but for me they are not so good. This is the second time I took night shot seriously. For day time at f1.8 portrait style taken in the morning when the suns barely up, that was sharp photo. So yeah I don't know what it is fully. I think it is just wide open facing the light that should be avoided.