Originally posted by newarts The thing that made me think reflection from the sensor is involved in the original posting is the ghost image is up-side down with respect to the primary image & is in pretty good focus.
The article referred to by Class A explains clearly what might be going on.
Flare
Dave
PS it even predicts a decreased ghost image with smaller aperture reported later by OP.
This article very clearly states, that the culprit is the filter, though it makes reference to the film as a mirror for the incident light.
Whether film or the sensor contribute much to the image formation is open to question, but sure possble. But the detrimental ghost image is clearly - and the referenced article states that expressedly - formed by the filter.
There is one big caveat about the efficiency of the film/sensor as a strong reflective light source and that is (especially with the lens here in question), that the accompanying graphics only references a thin lens construction. A zoom or super-zoom is much more complicated, especially when made for digital, as these tend to be designed as a telecentric lens system, which has a different ray trace, than the simple example on the the web page.
Anyway: if the sensor would be a major contributor to this kind of ghosting and flare, there wouldn't be much, we could do about it. Luckily, at least my personal experience with Pentax DSLRs is otherise, as I never have seen any sensor induced flare in my images. All the flring I have had could easily be traced to the lens in question, for example the old K 15/3.5, which is a wonderfully sharp and contrasty lens, but very prone to flaring.
I think, the conclusion in the referenced article is something, that is still underappreciated, especially by beginners: use a good lens hood all the time! Considering, that for instance, the K-m comes with a kit lens, which lacks the hood, this can be a real quality killer and the aspiring photographer will not even have a clue, why his images turn out insufficient.
Ben