# Expo/disc: royal rip-off

Started Feb 13, 2003 | Discussions thread
Re:simple and elegant solution

Guillaume,

Sorry for the late response as I stay on the other side of the planet.

OK let me explain,

1. if you are in broad daylight but UNDER shade and taking shots of something UNDER the shade. The lighting that really reaches the subject under the shade is that of the rest of the sky at that time, it may be blue or cloudy. Usually a high color temperature. (Nb: its different if you are under shade and shooting at something outside under normal sunlight. For this just use #3, see below)

WRONG: If you go and point at the sun and use that as a basis for CWB. It should give you a perfect 6500K BUT the shaded subject is not lit by the sun but the light of the sky, i.e. high color temp.

RIGHT: Point at the primary light source from the point of view of the subject, you can kneel there and look if you must but soon experience will tell you where the main light source is. Point and shoot there to get a basis for CWB that would be correct and it could be as high as 11000K and it varies.

2. If the sky is overcast/with clouds blocking sun but with blue sky.

Just aim at the brightest part of the sky, usually the area surrounding the blocked sun(I say usually). Get a correct CWB info from there. The subject in the open under this light is a fair mixture of blue sky and grey/white clouds. The result is probably better than the AWB. But if the sun is completely blocked by a thick grey cloud,the other parts of the sky will become the dominant light source. In this case, point there for CWB. Experience will tell you where. No hard and fast rule.

3. In broad daylight and the subject is lit by direct sunlight. Take the CWB by pointing directly at sun. OR just choose daylight setting. There may be slight differences because of the influence of a blue sky. You choose.

4. In the shade, with light reflecting off a building wall that has a hue or color. there will be 2 or 3 sources of light. Go to the level of the subject and see where the main light is coming from. Point there and get CWB reading. Its probably a compromise at best but it may be better than AWB or just use normal CWB proceedure with white paper or grey card.

5. Incandescent lighting. Just take CWB reading from the light source.

6. Mixed home lighting. Good luck.... I would suggest getting a white paper or something really white and place it over the subject and then go use the normal CWB proceedure with/without the expodisc. Or you can try to use the expodisc by pointing at the mixed lighting, the expodisc can also get it wrong here but oftentimes its right.

Exposure setting? I don't use the expo disc for exposure setting. I use the histogram...very useful. As long as you can capture the entire lighting range you can easily correct with PS unlike doing color correction.

Note: when I say go take a shot of the sky or sun or subject, you are not getting an image. Just a homogeneously lit/mixed frame that contains the color temperature/tint of the light source. That is what the expodisc does. BTW for you to get the camera to shoot this CWB frame you have to switch to manual focus then switch back to get your shot of the subject after loading it in CWB menu. An irritation but its the only way.

Somehow using the expodisc manages to outdo the normal CWB proceedure in almost all cases even in mixed lighting. I wish I had an objective answer for you but I am still learning too.

AL

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