The T2 - 39mm Step-Down Ring from Heliopan is for the old T2 lens mount. 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 52 - 49mm Step-Down Ring would allow you to use 49mm 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. However, it should be noted that care must be taken when using Step-Down Rings in order to avoid vignetting.
