A 52mm-Series 7 Step-Up Ring is a reliable and economical way to use filters. Using this ring saves you money since you won't have to buy the same filter two times for two different sized lenses. For example, a 52mm - Series 7 Step Up Ring would allow you to use Series 7 (54mm) filters on lenses with a 52mm front filter thread size. A series of these reasonably-priced adapter rings is far less expensive than buying the same filter in two sizes.
Small, efficient way to save space and money at the same time.
Allows user to buy fewer filters but continue to shoot the images they want.