Pentax 6x7 polarizing filter

[steve_cook]

I'm interested in opinions and experiences with the

Pentax circular polarizing filter for the 6x7 camera.

I've narrowed it down to either the Pentax filter or

the B+W Kaesemann circular filter. This filter will be

used on both my 55mm and 200 lens.

 

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Thank you,

Steve Cook

[tom_applegate]

Along with your questions I would like to know if the circular polarizing filter is needed with the 67/TTL finder system, being that it doesn't have auto focus?

 

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Tom Applegate

[michael_mahoney]

I am using a B+W linear pol filter on both my 45 and 75 lenses and it works fine, with the exception of ocassional loosening of the outside ring that holds the glass.

You will not need a circular pol filter as the P67 is of course not autofocus but as a matter of interest, the linear pol works fine with my Nikon 90 autofocus with both the 300 f4 and a Sigma 70-210 2.8.

[joel_collins]

I've also heard that, in addition to messing-up autofocus operation, using a linear polarizing filter on a camera with a beam-splitting light meter can lead to incorrect exposures. It's my understanding that the P67 TTL meter is not a beam-splitting meter, but most sophisitcated 35mm SLRs are. Has anyone experienced exposure problems like this? I'm suprised that the Nikon N90 works with a linear polorizer. Is this a conspiracy by the ciricular polarizer makers?

 

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Anyway, if the P67 doesn't need a circular one, why does Pentax make one for the P67?

 

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Joel Collins | jwc3@mindspring.com | http://www.mindspring.com/~jwc3

[garrett_adams]

It's in the product line because their 35mm long lenses require

circular polarizers. Of course now the soon to be released Pentax

67II also will also require circular polarizers.

[ben_greenberg]

I have just purchased the Pentax 67II and the manual says I must use a circular polarizing filter. I have been using, I think, a linear polarizer with my old P67's and I don't want to have to buy a new 82mm polarizer if I don't have to. Do I need to if I plan to use the metering system built in the AE finder?

[mark_harralson]

I contacted Pentax to ask if a circular polarizer was required for the 67II AE prism finder, and they told me it was not. After I read this series of messages stating that the owners manual said a circular polarizer was required I called them back and asked again. They said that if the manual stated that requirement, it was incorrect, and that a linear polarizer would work.

 

Was the comment in the manual specific to the AE finder? Have you tried a linear polarizer?

 

Any information would be appreciated.

Thanks, Mark

[mark_kremer]

Does anyone have any more information regarding using a linear 95mm polarizer on a Pentax 67II w/ the AE Prism?

[chicodovale]

Does anybody could please explain me what is the difference between circular and linear polarizer? I also have a Pentax 6x7 with two lens (55mm and 105mm) and I am also interested on filters for those lens.

Thanks

Chico

[richard_reddy]

What is the difference between a linear and a circular polarizer? This is physics, having to do with the time evolution of vibration directions for waves of light (and all EM radiation) in three dimensions. Since polarization is perpendicular to the direction of light propagation, it is treated as x,y components on a plane. You could have linear polarized light--often called x-polarized or y-polarized along an axis (or in between at some angle) That's linear polarization. If linear polarized light is coming right at you, it would (theoretically) look like a line (oscillating from zero to maximum amplitude) as it approaches you. From a position to your right

or left, it would look like a moving sine wave on a plane. This is like looking a sheet of paper from edge (direction of propagation) or the side--not so difficult to visualize. You could rotate the paper vertically, horizontally or somewhere in between, and the edge will look like a line with a particular orientation in space as it approaches you.

 

Polarization describes the electric field of the wave. Every E-field

also a B-field (magnetic), also polarized, but we don't need to worry about that because it's oriented at 90 degrees. If you know one, you know the other. In photography, we always mean polarization of the electric field.

 

Getting back to the sine wave, two light waves can be out of phase.

Then you have circular or elliptical polarization. If the two waves are out of phase by 90 degrees and have the same amplitude (the height of the wave), we say they are circularly polarized. If they are out of phase by some other angle, or differ in amplitude, then the light is elliptically polarized. Two waves are just a quantitative and conceptual model--what we actually see is an ocean of waves spanning the visible spectrum, partially polarized (by reflection). All polarizers block light that is not vibrating in a specific direction,

which is why you compensate by 1/2 to 1 1/2 stops for less intensity.

 

You can also visualize circular/elliptical wave fronts. Coming right at you circular polarized would scribe a circle, and elliptical polarization would scribe an ellipse. From the side, as the waves pass by, you would see a Helix for circular polarized light, and a "squashed" helix for elliptically polarized light, as the wave progresses in time.

 

If it all seems strange and complicated, that is definitely the flavor

of graduate physics. Polarization and the time evolution of waves in space relies upon Maxwell's Equations, The Schrodinger Equation, and quantum mechanics. Mathematics dominates the picture, and many other physical properties come into play. So there is a devil in the details that optical engineers who make our equipment must certainly contend with.

 

So the easy answer is that polarization is the direction of the electrical field as it travels through space, oscillating at a particular frequency, with a specific wavelength(color). Intensity is

constantly changing, so camera meters are really giving you a time average of light intensity. Direction can be visualized as a line, circle or ellipse--and circular polarization is really a special case of the ellipse where phase differs by 90 degrees.

 

You don't need to know this to do photography. Knowing light visually is something of itself. Personally I get more use of contrast filters

for B&W film than those expensive polarizers.

 

One very good thing to know is that you don't need a lens hood if a

polarizer is attached to the front of the lens, because side light cannot get through the polarizer. One large polarizer, with appropriate step-down adapters, will cover a range of lenses--and the adapters are very cheap.

 

The same strategy will work for other filters--if we just pause to use

our eyes. Side light generally is typically coming from one direction, usually near the sun. When taking a picture without a lens

hood, use your hand, a clip-board, notebook, or magazine to cast a shadow on the front of the lens. I get very good use of 105mm filters

on 82mm, 77mm, and 67mm Pentax and Fuji lenses. Nobody in the world will know that you used a copy of Newsweek as a lens shade. Since filters are so expensive, it's better to improvise and save your money

for optics or camera bodies.

 

Even a good filter is more glass in your optical path, so I use them conservatively. Lens hoods are desirable--but frequently ineffective

anyway--especially with wide angle lenses--where blocking the light yourself outside the field of the lens is more effective than a hood.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[richard_reddy]

One minor point. Linear and circular polarizers are doing exactly the same job. I think anyone will be fine using a linear polarizer on a

Pentax 67II, with any of the three available metering patterns. Since exposure measurements are time-averaged values of light intensity, exposure errors are extremely unlikely, even with the 2 percent spot meter (which is an enormous area when looking at light propagation).

 

For autofocus cameras, you're on your own. I adapt 67II lenses to my

Canon bodies because I prefer manual aperture and focus.