Cir. polorizer question

stradibarrius · Sep 16, 2009

I need a CPL for my RB67. I know a screw on 77mm would be very expensive. I do have a Cokin holder form my neutral density filters. I wondered if the is a polorizer that fits these holders and how good they work?

Steve Smith · Sep 16, 2009

A normal polariser will be fine for an RB67. You don't need a circular version. May save a little money that way.

I have a polariser for my Cokin holder. It sits in the narrower slot closest to the lens.

Steve.

mpirie · Sep 16, 2009

I think circular polarisers were designed for auto-focus cameras, so the normal Cokin Pola will work on the RB.

However, the point of the Cokin system is the transferability between systems so it may be worth going the extra for a circular if there's a chance you'll use it on an autofocus camera in future?

Fotoguy20d · Sep 16, 2009

stradibarrius said:
I know a screw on 77mm would be very expensive.

I bought two Hoya HMC CPs in 77mm from an ebay store named Sobefoto - I remember it being on the order of $80 each. Not cheap, but not too expensive (a subjective thing) and far better than the NYC mail order places as I recall.

Dan

stradibarrius · Sep 16, 2009

I was under the impression that the thing that mad a Cir polarizer circular was that you could turn it. Just like tilting you head with polarized sunglasses. since the Cokin holder will turn on the mount you basically have the same thing. What is the difference between a circular polarizer and a regular polarizer?

Q.G. · Sep 16, 2009

A circular polarizer is a linear polarizer with a plate behind it that "unpolarizes" the light that passed through the polarizer again.
It does that by turning linear polarized light into circular (rather elliptical) polarized light, hence the name.
(Simplified: ) In linear polarized light, the light waves oscillate in one direction perpendicular to the direction of travel, while in circular polarized light the direction of oscillation rotates ("corkscrews") around the direction of travel.

Both types need to be turned to find the angle at which the effect is as desired.

A circular polarizer is needed when there are components behind the filter that are sensitive to polarized light, such as some metering systems that use reflection/mirrors to get the light to the cell, or some autofocus mechanisms.

stradibarrius · Sep 16, 2009

Thanks, I understand now. With my RB I don't really need a CPL a linear will work fine...

Rick A · Sep 16, 2009

Olympus OM systam requires circular polarizers due to tha light sensor located behind the mirror. Linnear polarizers cause improper metering. This is usually not a problem with medium format slr's.
Rick

Cir. polorizer question

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