Heliopan filter adapter allows you to mount a larger filter on a smaller lens. (Although you can put a smaller filter on a larger lens if you really need to - just not more that one step smaller!). That means that if you have a lens with a diameter of 55mm, and another one with 52mm, your best bet is to get all filters in 55mm and then buy an adapter.
Be careful - with extreme wide angle lenses (wider than 24mm) you should test to make sure than ther is no vignetting around the edges. Especially when you're combining an adapter with a filter and lens hood.
If you need a Heliopan filter or adapter that we don't currently stock, we'll be happy to special order it for you. Just let us know.
Please note that special orders cannot be returned.