Originally posted by Class A The thing is, here it needs two to tango: The filter and something else (most likely film/sensor) acting as mirrors.
Originally posted by Class A But these observations are compatible with the hypothesis that the sensor acts as a (weak) mirror. Without a filter or "bad" lens acting as a second mirror, the light reflected by the sensor does no harm.
Ah, you see - if the sensor reflects anything at all (obviously any plane surface reflects a bit of incident light and as the incoming and outgoing angles are equal, light that falls near perpendicular to the sensor plane will obviously be reflected). That was as much valid with film as it is with digital sensors. Nevertheless the article makes very clear, that this reflection is without consequence, unless there is the front filter, which is also plano-parallel (quite in contrast to the curved surfaces of the lens) and which seems to act like a projection screen to some degree.
But whether the sensor reflects anything or wheteher there is a lens internal reflection is basically of not much importance, because the culprit - as the article states very clearly - is the filter.
My original thinking was, that any remaining flare/ghosting/reflection, after removing the filter, might quite possibly be caused by the lens - especially as the original poster used a super-zoom with many lenses. Obviously we cannot remove the sensor from the equation, nor can we "remove" the lens. But using a lens with fewer lens elements usually reduces reflections drastically. This is as much a common sense approach as it is based on photographic experience and lastly optics. Wheteher the lenses/lens groups are the originators of these reflections or whether they re-reflect light coming from the sensor is secondary, if we are only concerned, how we can reduce flaring and ghosting.
Ben