Update…
Managed to do a quick test last night.
Flipped the filter over so that the filter glass was now about 3mm further back from the rear lens element.
Attached pic shows the effects of the filter in its 2 different positions.
Left hand pic – filter closer to lens
Right hand pic – filter further from lens
The vignetting/reflection effect seems to be less defined and demarcated in the right hand pic – looks more like a vignetting effect that could be dealt with by flats.
I’m too lazy for flats though!!!
