One of the most annoying aspects of using front-mounted circular filters is that there are many different common sizes, which can quickly add up in cost and make you carry around a bag with a bunch of different filters. Canon's unique Drop-In Filter EF-EOS R Mount Adapter solves that issue, allowing you to use a single ND or polarizing filter with any EF lens. This excellent video review takes a look at how it holds up in the real world.