Why and when you need a step-down ring
Step-down rings are not as widely used as step-up rings because, in most cases, the smaller filter sizes result in vignetting.
Are step up and step-down rings the same?
4 Answers. A step-up ring allows you to fit a filter that has threads larger than your lens. A step-down ring does the opposite (with possible vignetting issues). If you have 72mm lens threads and want to fit a 77mm filter, you need a step-up ring.
Can I stack step up rings?
You can stack multiple step-up rings together to achieve a larger thread size.
