Gray cards : the 12% - 18% controversy

Started Apr 13, 2013 | Questions thread
D Cox
Senior MemberPosts: 7,972
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Re: Gray cards : the 12% - 18% controversy
In reply to jande9, Apr 15, 2013

jande9 wrote:

One problem with using a grey card is that it doesn't compensate for the direction of the light.

If you are in a side lit situation and hold up a card facing your lens and take a reading off that, any 3 dimensional object like a face will have the lit side overexposed.

If you try and compensate for that and hold the card facing the light and take your reading, shaded parts of the image will be underexposed.

People often take readings off the back of their hands, white skin being around 18% reflectance, and then turn their hands towards or away from the light to see how their exposure will change.

Incident meters are often supplied with a hemispherical bulb over the light cell to try and integrate the illumination over a three dimensional object.

The Weston meter has a dome which is a more complex shape, to model a typical real object.

I used a Sekonic Studio Incident light meter for many years, and you could turn the bulb towards the light or away from the light to see how your exposure would change depending on what part of the object was most important to you.  i still have it and use it occasionally, and I marvel at how photographically pleasing my results are using it.

Yes, this is a good system.

Or one can use a spot meter to look at reflected light from various parts of the scene.

A digital camera acts as a reflected light meter, and one could say that each pixel is a spot meter.

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