All of the filters that we offer come in 77mm or 82mm thread by default.  Currently, we only offer 3 Step-up Rings and 1 Step-down Ring, that are compatible with our 77mm filters.  These do not work with our new 82mm filters. So, if you have a 77mm thread lens then you can screw our 77mm filter right on.  Otherwise here is how to make those adapters work...All lenses have a specific thread size listed on the lens itself.  You can find this number on the inside or the outside of your lens.  Once you have that number you can determine what Step-up or Step-down ring is right for you.  A Step-up Rings is needed when your lens thread size is lower than 77mm.  A Step-down Ring is needed when your thread size is bigger than 77mm. Click here to see our RING ADAPTER TUTORIAL on how our adapter rings work with our filters to fit your camera.  Although we only offer 4 sizes, you can find other sizes at Amazon or google the size needed from other online suppliers.EXAMPLE: Let's say you have the popular Canon 50mm f/1.4 lens.  The filter thread specifications read 58mm.  Our Prism Lens FX Filters only come in 77mm and 82mm.  Luckily, we have a 58-77mm Step-up ring.  You simply screw in the step-up ring to the front of the lens, and you are set.  Now you can screw any of our PLFX 77mm FX Filters on top of your 58mm lens.  The step-up ring simply increased your lens diameter and allowed you to attach a filter of a larger specification.  Step-down rings do the exact opposite of a step-up ring. They adjust a larger lens thread to accommodate a smaller filter.