Lately we’ve been getting a bunch of questions on 4.5″ polarizing filters. There are several variations which can get quite confusing for those that are not familiar with them.

So here’s a rundown on the essential parameters:

4.5 inch is in fact the same as 114mm. Different manufacturers use metric or imperial. Likewise, some manufacturers refer to 138mm as 5.5 inch. These are both round filters.

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