Phil, in fact that's essentially what I found on orbs research, that it has to do with the lens in the digital camera.
Plus other theories, one being, as Jeane says, that some orb pictures could have a different explanation.
Another theory is that it is dust. Put this can be considered excluded, as dust particles are not 100% round, while orbs are.
This also goes for the theory you presented: the fact that orbs are completely round, does not explain bouncing light in the optics and flare, which could manifest in any geometrical form.
The orbs photos I've got were all taken on different days in the same rooms, where-as they never appear on other photos taken in different places with the same camera. So all rather ... open to debate
