Why and when you would need a step-up ring
If you own an interchangeable-lens camera system, chances are you own more than one lens. What’s more, there's a good chance the filter thread diameter sizes of one or more of your lenses differ from the other lenses. For example, two lenses might have 58mm thread sizes, while the third lens might have a 49mm, 62mm, 67mm, or 77mm thread size. Then again, each of the thread sizes might be different. And the more lenses you own, the more likely this is going to be the case.
 
Once you go beyond the best-quality protector or UV filters to serve as basic protection, you may wish to use an additional filter such as a Circular Polarizer, ND, Graduated ND, etc.
 
The starting point for configuring a step-up ring system is to establish a pecking order from widest diameter thread size to the smallest. As an example, if you own three lenses—one with a 52mm thread, another with a 67mm thread, and a third with a 77mm thread—you want a filter to fit the widest diameter thread size, in this case 77mm, and a pair of step-up rings, 67-77mm and 52-77mm, to couple the larger 77mm filter to the smaller-diameter thread sizes.
 
Although thread size doesn’t affect image quality, it does have an impact on the number of filters and lens accessories you have to keep on hand, regardless of whether you are taking pictures indoors or out. Rather than purchasing multiples of every filter and lens accessory to go along with each of the thread sizes, consider purchasing a single, high-quality filter to fit the lens with the largest thread size along with step-up rings to adapt the larger filter to the lenses with smaller thread sizes.
 
 
It’s hard to knock the advantages of stepping rings. Simply stated, if you own lenses with varying filter-thread sizes, stepping rings weigh and cost less than multiples of comparable glass filters and lens accessories. You could say stepping rings are a win-win solution that should please both your wallet and your gear-besieged shoulders and back. While stepping rings can be stacked, it is best to use as few rings as possible to reduce the chances of vignetting or ghosting.