> > I don't think 'Clear glass' filters exist. What would be their purpose?
I've got three. The large one came with my A* 300/f2.8, and is simply to protect the front element from dust, dirt, and suchlike. The other two are for use with internal filter holders (as on the A* 300), so there is always a glass element in the optical path even when I'm not using one of the 'real' filters.
