I’m a big fan of step-up rings. I buy all my circular filters in 77mm diameter (the largest diameter of all the lenses I own) and then use step-up rings to be able to use them on lenses with a smaller diameter. It’s a great approach that saves you an absolute fortune because you don’t have to buy your polarizers and variable NDs in five different sizes. You buy the largest size you need and then spend $1-2 each on step-up rings.
But this new device, the REVORING looks like it wants to be the only step up ring you’ll ever need. It’s currently launching on Kickstarter, where it’s already more than quadrupled its goal, and it’s a pretty interesting concept. Although, it’s not going to be ideal for everybody just yet.