The answer to this question will depend on a few factors, but in general the filter size should be based on the thread diameter of the lens you intend to use the filter on. Lenses will typically list their thread diameter on the body of the lens itself, either on the front next to the glass, or on the side along with the other specifications. To find the thread diameter on your lens, check the filter size tool on our website:
Find Your Filter Size
Alternatively, search for a number next to a symbol that looks like a circle with a line struck through ("Ø"). In the image below, it's visible in the 6-o'clock position:
The lens above reads "Ø58mm", so it has a 58mm thread diameter. We make some filter models in this diameter, and it's also possible to use one or more step-up rings to make larger filters compatible. Step-up rings are adapters that will make the threading on the front of your lens larger, so a larger filter diameter can be installed.
In the above image, the lens thread size is 67mm, but the filter thread size is 82mm, so a 67-82mm Step-Up Ring is in use.
If you have more than one lens, and the thread diameters vary between them (i.e. one lens has a 67mm thread and one has a 77mm thread), step-up rings can also be used as a way to make a single filter size work across multiple lens thread diameters. This tends to be more cost-effective than purchasing filters in multiple sizes. In the example above, where the user has lenses with 67mm and 77mm diameters respectively, they would be able to go with the 77mm filter size, and pick up a 67-77mm step-up ring. The 77mm filter could then be installed on either lens, meaning there would be no need to pick up a separate 67mm filter. For more detail on step-up rings, check out the following video:
Generally speaking, if you are working with a single lens then it is ideal to find a filter in a matching (or as close as possible) diameter. If you are working with multiple lenses, we'd recommend determining what the largest filter size is that you'll need, and then picking up any step-up rings you need to make the filter(s) compatible with any smaller lenses.
Questions, comments, or concerns? Send a quick email to support@polarpro.com and we'll be happy to help out.