I recently passed by WPPI Las Vegas and David from XUMEAdpters.com was there exhibiting the XUME Filter Adapters. These adapters have been around for a few years, but I thought we'd revisit the product now that cameras like the Sony A7s are hugely dependent on ND Filters when working outdoors with S-Log with it's minimum ISO of 3200.
I'm a big fan of Variable ND Filters on my cameras when outdoors, but I really hate unscrewing them when moving to shaded areas or indoors. The XUME Adapter kits allow you fast installation and removal of your filters. In order for the system to work you'll need a lens adapter (ideally placed on every lens) + a Filter Holder (ideally on every filter you plan to use). This can add up to be quite an expense if you want to convert everything you own, but personally I only find myself working with a handful of lenses outdoors and mainly 1 or 2 filters. With that in mind the XUME Pro Kit should cover most of your needs and would be a huge time saver.
As noted in the video, once the XUME Lens Adapter is placed onto your lens, your typical lens cap won't work directly. You'll need to utilize one of the XUME Filter Holders for the cap, or opt in for one of their new custom XUME Lens Caps.
Obviously many of use different lenses that may have varying filter sizes. My Sigma uses a 72mm, my Canon uses a 77mm, and my Lumix 58mm. Of course a simple fix to this is to purchase step-up filter rings so that all of your lenses share a common Filter Size. I typically step all of my lenses up to 77mm (as seen here), but this does mean you have to buy several 77mm Lens Caps - very cheap via eBay. The complete line of XUME Adapters and Kits are available via B&H (click here).
XUME Magnetic Quick Release Filter Adapters