Polarizer question

[rafael_macia]

Hello,

I just acquired a Series VII drop in circular polarizer. (13370). I plan on using it with the 400 and 560 6.8 Telyts.
The filter has a small yellow dot on one of the side rims (metal). It is on the more flush (glass), to the surface of the filter side. When I put the filter up to my eye to see its effects, looking through one side vastly differs in strength of effect, than from the other.

It looks to me that the dot side should be closest to the camera body.

Is ther a rule to follow? Or should I just "eyeball it"? (no pun inntended)

Thank you

Rafael

[Martin K]

Hi,
The circular polarizer is actually a linear polarizer combined with a retarder plate to ensure that the light wave emerges out of the polarizer in a "circular" way, i.e. unpolarized. So you first polarize the light to get rid of unwanted reflections, and then de-polarize it again. Otherwise the light measurement of the Leica SLR and R cameras will give the wrong result due to further polarizing action of the semitransparent mirror that syphons off some light for measurement. The yellow dot identifies the back of the polarizer, should therefore always be facing the film plane. Regards, Martin

[rafael_macia]

Martin,

Thank you.

Rafael

[robsteve]

The reference marks on most polarizers also are aligned so that if the mark is pointed in the direction of the sun, you will have maximum polarization. On B+W filters, the reference is the engraved B+W. I suspect the yellow dot on the Leica filter also serves this purpose in addition to the film orientation.

[rafael_macia]

Rob, never knew that.
With the "drop-in" aspect, though, it gets complicated. My plan was to eyeball the scene with the polarizer in front of my eye. Then drop it in, hopefully keeping the same position.

I think what I will do is tape numbers around the filter edge, and when the effect looks correct; look up, note the number, and position the filter in the drop in slot with the same # up top.

An early Leica filter, used that principal. Looking by eye first. then putting the filter on the lens. Then revolving the filter to position the correct # back up on top. (The outer rim of the filter was engraved with numbers The fliter was a screw in polarizer with a rotating mount. Leica # 13352 "POOTR".

Rafael