Circular or Linear Polarizer

[poff]

<I suspect a linear polarizer will be satisfactory with this camera, but I would like to confirm it. Does anyone know the authoritative answer, or perhaps can someone suggest a conclusive way of testing?>

A very simple one-minute test can be performed right at the photography store:
1. Attach the linear polarizer to the lens.
2. Switch your camera to the spot-metering mode.
3. Direct the lens at a non-glossy surface (a brick wall, a sheet of paper, or alike).
4. Adjust the aperture, so that the shutter speed reading should be in the middle of the range or higher.
5. Watching the shutter speed reading rotate the rim of the linear polarizer.
If the reading remains the same (or it is changing 1/2 or 1 step in the case the surface you direct the lens at is nevertheless glossy), your camera will perfectly work with a linear polarizer.
If the reading is changing dramatically while you are rotating the rim – from the normal to no light at all – your spotmeter requires a circular polarizer.

You can do a similar procedure to check whether your autofocus works with a linear polarizer or not.

Finally a few notes:
1. I know from experience Contax ST does not need a CPL, though it has a spotmeter.
2. The official www.contaxcameras site says the G2 does not need a CPL either. Pay your attention to the fact that the G2 features both spot-metering and combined passive+active autofocus.

Andre Shipoff

 

[mike_nunan]

Hi Andre,

Thanks for that suggestion. I have an RTS II which doesn't even have a spot meter, but the behaviour when I attempted a test similar to yours was a bit unexpected. There was around a half-stop of variation in the meter reading, despite the fact that the camera was aimed at a blank expanse of matt-painted interior wall. I persisted in trying to get a final answer out of Kyocera, but they stopped replying to my mails when I asked them to be more specific, and to account for the half-stop variation.

-= mike =-

 

[poff]

Hi Mike,

You wrote: "There was around a half-stop of variation in the meter reading, despite the fact that the camera was aimed at a blank
expanse of matt-painted interior wall."

I think, the incoming light was nevertheless a little bit polarized, and a circular polarizer would have behaved the same way. I encountered that phenomenon aiming the lens at some surfaces, at the same time other surfaces did not give any change in the reading at all.

Andre Shipoff

 

[tbc]

> Hi Mike, > You wrote: "There was around a half-stop of variation in the meter > reading, despite the fact that the camera was aimed at a blank > expanse of matt-painted interior wall."

Remember that any polarizer has a variable filter factor. So, depending on how you orient the filter, it will filter more or less light. That's why when the light source is at right angles to you, a polarizer will be most effective. So variation when you set the position of the filter is normal.

 

[mike_nunan]

Hi Andre and Tom,

Thanks for that. I had another go at my experiment with the blank wall over the weekend, and I'm pleased to report that there was zero variation in exposure reading this time around. I can only assume that the light was a bit directional on my first attempt.

Best regards,

-= mike =-