Thanks to all who contributed to this tread - I now have a new 2" DGM - a birthday gift
. Of course it is cloudy now so my apologies to you all for that.
BTW Is it normal that these filters look like they are dusty on delivery, I tried a blower to remove but to no effect - I imagine the mirror-like coatings are quite likely to emphasise the dirt but I thought it should be pristine out of the box - anyone out there care to share?