If you use many different lenses on your camera and do not use a fully rigged mattebox, you will usually need several (ND) filters, each with different diameters, or several filter adapters. With the variable filter adapter REVORING from H&Y, which is currently offered on Kickstarter, it should be possible to mount larger filters in front of lenses with various smaller diameters.
It is simply attached to the front of the lens using a special screw mechanism and is available in three sizes, 37-49mm, 46-62mm, 67-82mm, to fit the three filter sizes 52mm, 67mm and 82mm respectively. If pre-orders worth at least 500,000 US dollars are received, a Revoring for lens diameters of 82-95mm is also available (stretch goal).
The Revoring is compatible with ND filters from other manufacturers, but a combined variable ND + circular polarizing filter can also be ordered in the required three sizes (52 mm, 67 mm, 82 mm). The ND filter thickness can be varied between ND3 and ND1000, corresponding to 1.5 to 10 f-stops. The ND filter is made of Schott glass B270 and has a hard stop.
The filter adapter is available for , or depending on the size, in stores it should cost or later. The VND+CPL filter is available on Kickstarter for 139, 144 or 149 dollars instead of later for 184, 189 or 199 dollars. Sets are also available. Please note the usual crowdfunding risk (however, H&Y has already had a successful Kickstarter product launch).