Snow metering with a Polarizer

Here's my story.

 

I thought, that when you get a polarizer it reduced the reflections,

which is true, but I assumed it would tame the reflections of the

snow so that it could be metered normally, I was wrong... I think.

 

From what I understand, good snow metering is acheived by metering

off of the midtones of the snow, then overexposing 1 1/2 - 2 stops

because the reflections off the snow make the meter think the scene

is brighter.

 

But with a polarizer, should I still correct my exposure? I've only

seen my results from this once since it's taken forever to get my

slides back. But with that one photo, the snow was overexposed in an

ugly way, and I think it was because I was using center weighted avg

metering and metered at the scene I had composed, which would have

metered then trees, THEN I exposed +1 stop.

 

So what I'm getting at, is, when using a polarizer, should I be

metering off the snow and compensating with +1 1/2 - +2 stops, or

would it be changed due to the polarizer?

Polarizers are a through-the-lens effect, if you will, which means that both you and your meter see the same thing. Of course, it also means that corrections you would have made without the polarizer would also be made with it, based on how you want the image to look.

 

For what it's worth, I think there's one terminology thing to correct. If you're metering off midtones, you don't need to correct, since your camera's meter treats whatever it's looking at as midtones. The issue with snow is that you're metering off something far brighter than middle-grey.

 

Hope that helps. Enjoy.

As Marshall said, the <I>method</I> of metering with a TTL meter doesn't change when you use a polarizer (or any other filter). Since it's on the end of the lens, the meter is "looking through" the filter, so compensation is automatic.

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You'll notice a slower shutter speed when you use a polarizer or colored filter versus when you don't. That's because the camera is compensating for the filter automatically.

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Take solace in the fact that eventually, metering won't be too difficult for you. However, it can be confusing at first, especially with a subject like sunlit snow. If you have several TTL metering options with your camera (e.g., matrix/evaluative, center-weight, and spot), then try using them all before you shoot to see how closely they agree. The evaluative meters of modern cameras are very good -- if you're metering correctly in center-weight and spot modes, you'll probably end up with results very close to what the evaluative meter suggests for the scene.

be very careful using polarizer in snow, the sky can become very dark. Thats not your problem is it?

I agree, be careful of polarizers anytime especially snow or white objects for that matter. They really seem to "muddy" things up, removing all detail from underexposed areas and reducing contrast in bright areas. Despite TTL metering they also seem to require added exposure. Every polarized shot I ever took looked like it was 1/2 to 1 stop underexposed even though they are supposed to operate fully with TTL. Also it may be that your camera's lightmeter system needs a Circular Polarizer (most of them now do) so check that you're using the right type. I know they can have wonderful effects for Meditteranean/Caribean waters and create grossly blue skies but I remain sceptical about their usefulness.

I almost always use an incident light meter around snow, then add the filter factor of +1.5 (i.e, I lighten the exposure since a handheld meter doesn't compensate like a TTL meter does.) Be aware that a polarizer is not a set amount either. Sometimes it only eats 1 stop; usually it eats 1.5 stops, but sometimes they seem to gobble a little bit more than 1.5. I generally bracket +/- 0.5 stops when I can, from +1.5 as the basis.

 

Kent in SD

1. I don't think there really are and "midtones" in snow, are there? :o) When you're metering snow, find the <I>brightest</I> area in the snow. Meter that area, then open up 1 1/2 to 2 stops; this will place the brightest area -- the highlight -- near the upper edge of the film's range, right where you want it.<P>

2. A polarizer <I>always</I> has a filter factor and it is <I>always</I> the same. (Factor will vary a bit between brands.)<BR>

Something like 1 2/3 stops up to 2 1/3 stops depending on brand. Remember that the non-polarized areas of the scene (people, cows, most trees, etc.) don't change as you rotate the polarizer, so you always have to apply the filter factor to get the exposure right for those subjects. Snow, BTW, is essentially non-polarized because the reflecting surfaces of the grains are randomly oriented...

Ok, Alan helped because he answered what I wanted to know, which wasn't how to use a polarizer, I knew how to do that already, thanks.

 

The thing I was wondering was, since the polarizer will reduce the reflections, it would obviously be reducing the contrast and brightness of the snow, so I didn't know how much it was going to "trick" the meter (think the scene is brigter than it is). Here's what I'm going to try tomorrow (assuming it's a sunny day):

 

Take 1/2 of my photos with my polarizer, meter on the snow and open up 1 - 1 1/2 stops. Then take the other half without (never done this before), meter off the snow, and open up the same amount, just as a comparison.

 

Thanks for your help.

Listen to Alan. He's got the method. What you did was double compensate by metering off mid-tones then opening up. For snow (on slide film) using the zone system (that's what this excercise is about), first use spot metering if you can. Meter off the "brightest areas that you want to preserve detail". I put that in quotes because I've read/heard those words together like that many, many times. Then open up 1-1/2 to 2-1/3 (only use the 2-1/3 end if you're using print film). This application is just the opposite of the number one use for the zone system. Metering for the deepest shadows of interest and closing up to bring them down to zone 3 or thereabouts. BTW I think it's important to spotmeter because you know what you are metering. If you can only get to centerweight metering mode, get close enough to the snow to fill the frame with it and essentially use it as a spotmeter.

Alan, wouldn't the polarizer's filter factor vary depending on how much polarization you apply by rotating the filter?

Steve:

 

Lots of good advice in the posts here.

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Your first decision (after you have decided on how to compose the scene) is to decide whether or not to polarize, and if so, how much. Look at the scene through your camera and rotate the polarizing filter to get the AMOUNT of affect that you want. This varies from place to place and from time to time. Somtimes I polarize and sometimes I don't. On some cloudy days with no sky showing at all in the final photo, a polarizing filter is a lifesaver at removing glare from foliage.

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In Michigan, I usually polarize more in the summer than in the winter. In Colorado I usually polarize less than in Michigan. I polartize less at higher elevations on ultra clear days. On some days in Big Bend National Park, a polarizer can turn a blue sky into black. Very dramatic but maybe not what you want.

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Your second decision is how light or dark you want your most important snow to be. On a bright sunny day, I prefer a lighter toned snow than on a cloudy day, or a photo entirely in the shade, or at dusk.

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Put your camera on MANUAL exposure, and, as has already been said, METER ONLY THE SNOW! Decide how light you want it to be and compensate accordingly. For medium toned snow at dusk, do not compensate from your basic meter reading. For lighter snow, add 1/2 to 1 1/2 stops of light, maybe more. Season to taste! You will learn by experience.

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If I do this right, a photo of light, medium, and dark toned snow will follow.

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<img src="http://www.jimdoty.com/Nature/Colorado/Colorado_Winter/AWY29wr3__SpPksLV.jpg">

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There is no hard and fast rule as to how light snow should be.

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Coincidentally, the above photo was not taken with a polarizing filter, even though I consider it to be my most valuable filter.

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Happy Snow Shooting!

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Jim

<I>...wouldn't the polarizer's filter factor vary depending on how much polarization you apply by rotating the filter?</I><P>

No. That's a common misconception about polarizers. Remember that practically all scenes have areas with polarized light AND areas where the light is non-polarized. In the areas where the light is non-polarized, turning the filter has NO EFFECT, that is, it acts like a ND filter in those areas. So you apply the filter factor of 2 stops or so, in order to retain correct exposure in the non-polarized areas. Then you turn the filter to vary the amount of the effect in the polarized areas. If you change the filter factor, then you will get incorrect exposure in the non-polarized areas of the scene.

Alan, thanks for the explanation.

 

Jim is that the Spanish Peaks and La Veta? Regardless of the location, it's a great photo.

Rich:

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Thanks for the complement.

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Yes, it is the Spanish Peaks and LaVeta, Colorado. The brief story behind this photo is here: <a href="http://jimdoty.com/Nature/Colorado/Colorado_Winter/colorado_winter.html"> jimdoty.com/Nature/Colorado/Colorado_Winter/colorado_winter.html</a>.

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Jim