The Dream FX Lens Filter, the Blue Flare FX Lens Filter and the Centrefold Split Diopter Lens by Prism Lens FX are currently only available in 77mm (as the default).
The step up lens filter adapter ring will adjust a lens thread size between 67mm to 77mm to accommodate these lenses.
How to find your lens thread size:
To see the thread size of your lens, you can find this number on the inside or outside of your lens. The first number denotes the filter thread specification of the lens on which the step-up ring is to be used. The second number denotes the filter diameter specification that will be screwed onto the wider end of the ring.
Once you know that, you will know if you need to get a step-up or a step-down adapter ring.
If your lens is larger than 77mm, you will need the Step-Down Lens Filter Adapter Ring.
The step-up lens filter adapter ring sizes that we currently carry are:
Are step-up and step-down rings the same?
The step-up adapter ring simply increases the lens diameter and allows you to attach a filter of a larger specification so that you don’t have to buy or carry multiple filters for all the lenses you have. This will save you money and bulk.
Step-down rings do the exact opposite of a step-up ring. They adjust a larger lens thread to accommodate a smaller filter. When using step-down rings and filters, you may notice a lot of vignetting. Basically, the corners are getting less light because of the tunnel that is created.
More info can be found in this video by Prism Lens FX.