Where is the mark on the polarizer supposed to be?

Started 2 months ago | Questions thread
OP Dem Bell Regular Member • Posts: 330
Re: Where is the mark on the polarizer supposed to be?

ThrillaMozilla wrote:

And just to make the explanation more complicated, on photo filters a straight line passing through the center and the mark is perpendicular to the plane of polarization, so the mark does indeed point to the sun for maximum effect. In scientific instruments the mark is generally rotated by 90 degrees relative to that in photo filters.

Thank you for this. This is exactly what I wanted to check - that on a photographic polarizer the mark indicates the direction of maximum extinction rather than the direction of the transmission axis. Reading the replies, there seems to be an agreement on that. Thanks everyone.

I double checked how firmly the glass is sitting in the front rim in the three polarizers I tested. One of them was quite loose and could have been accidentally rotated during cleaning. One was possible to rotate if I got a good grip on the glass using rubber gloves. The third one was dead solid. So there is a chance that previous owners rotated the glass out of the correct orientation in 2 out of 3 filters.

This is how I identified the direction of "maximum effect":

Hold the polarizer at the eye level and look though it (from the same direction the camera would) at the reflection of the curtain in the window. Make sure the plane of the polarizer is about 60 degrees to the plane of the window. The light is travelling in the horizontal plane from the curtain to the window, gets polarized in vertical direction upon reflection and then travels towards the polarizer. If you rotate the polarizer so the reflection is completely removed, the top of the polarizer will correspond to the position of "maximum effect". When light is polarized in this orientation, the filter will not let it through. That's where I put a little blob of "Blue Tack" putty.

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