circular vs. linear polarizer on maxxum 5d

[vikramdmello]

hello,

 

i recently got a polarizer for my maxxum 5d. i've been reading about the

difference between circular and linear polarizers, and i'm not sure what i

have. the package does not specifically say linear or circular, and there is

no "C" on the filter ring before "PL". does that mean it's linear?

 

from what i understand, having a linear polarizer means i cannot trust the ttl

meter; is this correct? should i then just manually adjust 1-1/3 stop each

time i want to use the polarizer?

 

thank you for any insights/experience,

 

vikram.

[nick_evans1]

If you have a 'C' in front of the PL then you probale have a circular polariser.

 

The difference between the Linear and Circular polarizers is the way the polarising glass was made. Circulars were made because the early autofocus systems would sometimes focus on the glass and not the subject you were photographing.

 

AS for the metering just stick it on and away you go the camera meter should be able to deal withe the poloriser without any problems.

 

Nick

[w.smith]

How about testing it out for yourself, Vikram? You would SEE whether aperture adjustment

is neccessary!

The proof of the pudding is in the eating.

[aaron meyer]

<<Circulars were made because the early autofocus systems would sometimes focus on the glass and not the subject you were photographing.>>

 

Actually, the reason is because AF and metering systems in modern cameras rely on their own polarizers inside the camera for their sensors. If a linear polarizer is turned 90 degrees out of phase with one of the camera's internal sensors, that sensor will read total darkness and therefore meter and focus incorrectly.

 

This is true of current systems as well.

 

Now, it you happen to have the polarizer spun to a non-interfering position, the camera will seem fine, but it's not guaranteed.

 

A circular polarizer effectively "un-polarizes" the light after it passes through the filter. It still allows only one polarity of light to pass through, but it re-scatters the light that does pass through rather than leaving it polarized inside the lens. This ensures proper focus and metering.

 

If you have AF, you need a circular polarizer for consistant results.

[ivan_dzo]

Vikram, I think we need to differentiate between focusing and exposure issues.

 

Certainly you may get autofocus issues with a Lin Pol with the 5d. I seldom use the AF anyway so don't get any problems.

 

Never had any exposure problems however using circ or linear polarisers.

[tom_montemarano]

I ran some tests a few years ago with my Maxxum 7. I tried positioning the sun at different positions (to side and behind), the camera in different orientations (landscape, portrait, 45deg) and polarizer angle. It was a blue sky day, and the camera was always pointed at the same section of blue sky.

 

There were differences between using a CP and Linear, but the worst case I measured was -2/3 stop for the linear with the camera held vertically and the polarizers oriented up. With the camera oriented at 45 deg (not a normal shooting position), I also got -2/3 but with the polarizer oriented to the horizon. In horizontal camera position the worst case was only -1/3 stop. The -2/3 stop could be significant for slide film, but not much else.

 

By the way, I did normalized for any inherent difference in density between the two filters in the least polarized direction. Also, since I use CPs on my AF cameras, I didn't do any more detailed follow up on these results or take actual shots where I got film developed.

 

Tom