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What does it mean when people take meter readings off grey cards. How is it done? I use my camera's meter and i usually measure the exposure from shadow areas using a spot meter, can I still do the grey card method.
Thanks for any contribution

Grey cards are 18% grey, which is middle ground for exposures. Normal grey cards reflect 18% of the light that falls on it, giving the scene "average lighting" (averaging out the lights and darks). To use a grey card, simply put it in the area of the photo that you would like to expose for (ie. shadows or highlights) and use your camera's metering system on it, instead of the whole scene.
This will work most of the time, but sometimes, like with snow, you will need to use common sense. If you use a grey card with snow, it will want to make the snow 18% grey. You need to allow more light into the scene to make the snow white again.

I hope this somewhat makes sense! I'm sure that others here will have more to add!

Kim's explanation is good except for couple of things :) The reason the card is 18% (a figure that is debated endlessly) is because they manfacturers set the meter in your camera to try to make your picture 'average' I have no idea how they come to that number but it will be explained somewhere! So, when you take a reading your camera gives you an exposure that will record the scene equivalent to mid grey. You point your camera at snow and it tries to make it grey, you point your camera at a black wall and it tries to make it grey. By metering a grey card your are showing the camera meter what it wants to see, and thus getting a 'true' indication of the exposure needed for the light in the scene. So, in Kim's example, metering a grey card in a snow scene, then using that meter reading to take the actual picture, you should end up with white snow. If you just metered the snow you'll get grey snow (don't go near yellow snow!) If you're spot metering shadows, you're trying to place those shadow areas at mid grey (Zone IV, I whisper!) What you should do then is reduce your expose by 1-2 stops to move that shadow area down the exposure scale and hope (or measure, since you've got a spot meter) the highlights to see that they will be within the films latitude. I use this method with a center weighted metered camera by walking up to the shadowed area that I still want detail in, then reduce exposure (by aperture or shutter or both) 2 stops and step back and recompose the scene.

Someone might come along and give a simple answer if you're lucky :)

Just a quick addition...

"18% grey" is supposed to mean that 18% of the light shining onto the object is reflected back toward the viewer. It just so happens that 18% reflection also happens to fall one half way between total white and total black on conventional film (ZONE V).

Through testing its has been determined that most "NORMAL" scenes happen to average a total of 18% reflection of the light, so auto-exposure cameras have been calibrated to meter normal scenes at the 18% reflectivity value. It has been argued that some camera meters are actually calibrated slightly more or less than 18% and therefor it is always advisable to test for yourself and decided where you like your cameras exposure to be for various scenes.

It also just so happens, that green grass, red barns, and many roads.. just happen to match the 18% grey reflectivity relatively closely.

You can expose for snow by metering the snow in the light you want the snow to appear "normal" and opening up 2 or 2.5 stops from the meter reading.

Normal white people's skin is typically 1 STOP more than 18% (or zone VI).

Film's can only record a certain amount of light ranges so it's your job as the photographer to decide how to expose each scene to satisfy your vision and record what u want on the given film's range. Most color neg film can record about 5 stops of light, and tranny (slide) film is a little less.

B&W films can record much more information depending on your developing method but enlarging paper is still only around 5 or 6 stops.

You can argue that my figures are wrong, and there are means to alter these limitations to some extent, but they are a really good starting point.

Hope I didn't add confusion to the subject.

-Dave

Why 18% Grey... because, in an average scene where most of the colors are available... Say, in a landscape where you have blue sky, green trees, black shadowed areas, brown rocks etc. etc. Assume all these colors are freshly painted (that is they are still wet) and use your hand and mix all these colors, you will end up with 18% grey world.

So, the light meters see 18% grey, no mater what the subject is. As explained here, whether it is snow or charcoal, the light meters see 18% grey and hence we would have to compensate the exposures by opening up (in case of snow) or closing down (in case of coal).

Hope this helps.

Thanks.

I hate to be a poop, but even though you are all saying the proper way to meter using a grey card, the fact is that average scene reflectance is only 13% not 18% and if you use a grey card to meter you should open up another half stop or so or your images may be just a tad dark unless you meter is calibrated for 13%.

The 18% grey card is not 18% reflectance. 18% grey is used in the printing industry as medium grey with relation to the size of the halftone dot coverage, not a level of reflectance.

I've read the views regarding 13% or 18% and whatever it is, the concept is the same. However, I can't convert '5' to Roman numerals too well! lol! Dave got it right!

Kerchingggg! (sound of 2 cents falling onto floor)

Hi Max,

You say you are using spot metering for shadows. I don't want to muddy the water (a sure sign that I am going to) but...

Spot metering should eliminate some of the gross errors that an average scene reading can generate. The classic metering pattern before all of the multipattern matrix stuff was typically 'centre weighted'. It was excellent for many situations with some caveats. If you were taking a landscape scene, the expanse of sky would usually affect the metering cell enough to underexpose your scene because it would seem too bright to the meter. The standard workaround was to tilt the camera downwards a little while metering so as to remove the influence of a vast bright area like the sky.

Because spot metering does not get influenced in the same way (although it is still a reflected reading and Dave and Nigel's comments are still valid when placing the matter you want on whichever zone you want) it is commonly perceived as a better way to take light value readings. You meter a specific tone think about where in the tonal range you want it to appear, make your settings and take the shot. I would suggest that grey card considerations are redundant for spot metering.

Just when you finally think that may be clear... it isn't :) If your spot meter is on the camera it is far more likely to be a partial area meter reading (anthing from 10% down to maybe 1% on very expensive cameras) It will still behave as described but a good trick is to fit a telephoto lens and meter throught it as the angle of view is less than say the 47degrees of a so-called standard 50mm lens.

Handheld meters that read spot readings typically read 1 degree angles of view (oldermetters may have been 5 degrees with the ability to take accessories to see just 1 degree. If you want really accurate exposure measurements you can try reading the tones in a scene by takeng an incident light reading. This measurement is of the amount of light falling on a scene as opposed to the amount of light reflected from it. You dont have to account for anything that might throw the reading off... except... if the scene is very distant you will need to spot meter or guess (sunny 16 rule etc) . If you wnat to use your camera you can but you will only be able to do this for scenes with easy reach because you have to point the camera from where the subject is towards where you want to take the scene from. This is often difficult.

The classic image of a movie director holding an exposure meter up to the face of a movie star is easy to understand. The device has a small translucent hemisphere for gathering the light from all directions and directing it on to the cell in the meter. The meter 'point's to where the camera will be set up. You can even get these hemisphere accesories to fit on the front of a lens so that in camera metering can be used as an incident reading exposure meter but I have no experience of any of them.

Sorry for the lengthy dialogue and I hope it helps.

Cheers!
Jeff

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