Hi everyone,

I would like to know if anyone who has a Pentax 67II has tried a linear polarizer on the camera and come up with good results.

I'm asking this because I e-mailed Pentax twice about this and they told me linear polarizers are okay. But another P67II user, Tapas, told me that a linear polarizer will screw up the built-in spot metering. And the P67II manual (which has MANY typos) also says that a circular polarizer is necessary, without going into the reasons.

Does anyone have a definite answer on the subject, i.e., has anyone tried both types of polarizers ?

Thanks, Marcelo

-- Marcelo P. Lima (MPL4@cornell.edu), February 28, 1999

Answers

I haven't bought one yet but I did phonr Pentax in Colorado and the tech rep confirmed that a linear pola would work fine.

-- Garrett Adams (gadams@jps.net), March 01, 1999.

The rule of thumb that I've always heard is that circular polarizers are only need for autofocus cameras. Since the P67II is not autofocus, you should be fine with the linear polarizer.

I'm not an optical engineer, but here's how I understand it to work: In autofocus cameras, the image is split into multiple "beams" that are then separately analyzed by the light meter and the autofocus sensor. A linear polarizer will prevent the "beam splitter" working, and the autofocus sensor will be "blind." Since there is only one sensor on a manual focus camera (the light meter), there is no need for the beam splitter, and thus no need for a circular polarizer.

Here's another idea: why don't you just go to a camera store and ask to see a P67II with a linear polarizer and then see if the meter works. Report back here if you have any news for us.

-- Joel Collins (jwc3@mindspring.com), July 07, 1999.

Guys, i've red the question and answers and have something to add : Olympus already advised many years ago to use the circulair pola for usage with OM2N, at that time there was no autofocus yet. What i will do is make two slides with both pola filters on a 55 mm lens and let you know the results in a week or two. My feeling says that i need the circulair for the matrix metering mode.

-- Milco van Klingeren (milco.vanklingeren@wang.com), July 14, 1999.

Linear polarizers can cause metering errors in systems, where the light meter reads light which is reflected off some nonmetall surface, most often the glass surface of the viewfinder. This problem can't exist, if the light meter cells read through the mirror or are somewhere else.

P67 has metering cells in the viewfinder, of course, and this means there could be problems. If Pentax techs say that the design is not affected by polarization, it propably is so.

Circular polarizers have '1/4 wavelength'-sheets of 'plastics' behind usual linear polarizing sheet, which gets the plane of polarization to rotate, so reflections are not affected of the direction of polarization - the main subject here is, that when the light comes to a surface, the reflecting amount of light coming depends of the polarization.

Intuitively (I really know nothing of the Pentax metering system) I'd suspect, that linear polarizers *could* cause metering errors with the spot metering mode....

Sakari

-- Sakari Makela (sakari.makela@koulut.vantaa.fi), August 13, 1999.

Oops - I forgot to say, that there is no physical reasons why the quality of the image could depend on the type of polarizer... the effect of the polarizer is actually the same. - If the quality of the filters is similar, of course.

Sakari

-- Sakari Mdkeld (sakari.makela@koulut.vantaa.fi), August 13, 1999.