Whitebalance and Exposure

[johnsy]

I want to photograph some mountains in the snow on Friday, I have just picked up 3 exposure cards (Grey, Black and White).

Am I correct in saying that I can place the cards somewhere in the foreground of the scene I want to shoot, switch my cameras white balance to manual and take a reading off the white card, then using manual exposure meter off the grey card to get a correct exposure?

 

[HoppyUK]

That's the theory. Your handbook will explain how to take a custom white balance. Very easy off a white or grey card, providing it is perfectly neutral, ie not warm or bluish but equal quantites of red, blue and green. And not so over-exposed that it's blown, or under-exposed and full of noise.

For exposure, the standard reference is 18% grey, which would then put that tone in the middle of the histogram - the theory being it would then give you maximum scope for highlights and shadows either side.

18% is always used for film, but digital varies a bit depending on how the camera is calibrated. 12% or 15% is also used, but never stated by manufacturers because digital sensors to not have a native sensitivity and ISO is created somewhat artificially with amplification gain.

It also depends on your definition of correct exposure, which varies according to subject, your priorities and subjective evaluation, and how you're going to post process.

If you want 'optimum' exposure (whatever that is) then the histogram and blinkies are the best guide. Check out Expose To The Right theory to make sure you max out the sensor. Explanation here http://www.luminous-landscape.com/tutorials/expose-right.shtml

 

[Scarecrow]

Personally I would use the grey card for custom white balance, as you risk overexposing one of the channels with a white card which will give you an incorrect setting.