PL-C52(WIII) reference marks for filter max/min

[r5user1]

I am trying to find out if canon designed a reference mark on the filter for locating the zero point, or the 90 degree point. When removed, I can see two small gaps in the ring that holds the glass element. These gaps are at opposite (180 degrees) sides on the ring. They also are very close to what my untrained eye set as the 90 degree mark. Is this just dumb luck or did Canon plan this?  #PL-C52(WIII)

[shadowsports · Accepted solution]

Greetings ,

There is no "zero" setting, but the marks you noted can be aligned to minimize the polarizing effect. In all cases, some degree of polarization will always be present with the filter inserted.  The degree will be determined by the angle of the sun or brightest light source.

Note also that some versions of this CPL had a service notice.

Canon Telephoto EF Lens Accessory To Users of Drop-in Circular Polarizing Filters PL-C52 and PL-C52(WII) - Canon Hong Kong https://share.google/Q8z6ZSCyhLIIryJxe