What is an 18% Gray Card verses a White Balance Card?18% Gray Card The 18% Gray Card’s main purpose is to allow users to make adjustments to their camera that affect or rather allow users to setup correct exposure at the beginning of any photo sessions. We use 18/% Gray because of the amount of light that is reflected off this card and how the cameras sensors interpret this data allows users to manually setup exposure that can be used in the RAW workflow with dSLR cameras or video cameras. Light meters work the same way using the 18% Gray as well. In other words the 18% Gray should only be used to check lighting ratios and lighting distribution to set exposure.
To use the card, place the 18% Gray Card by the subject you are shooting then setup the exposure using the cameras manual controls. This card is strictly used BEFORE the shoot to adjust for the specific lighting conditions and users really don't even need to shoot the image of the card - just make the camera adjustments. That’s all there is to it, the card’s main focus is lighting and setting up proper exposure.
The short answer to why we use 18% Gray is simply this, if the light in an average scene being photographed is averaged out, it will produce an 18% gray tone (neutral). So film cameras, dSLRs cameras, and video cameras are all formulated to produce proper exposure when exposed to produce an 18% gray tone. A great example of this is when shooting a landscape image that has a very light sky but the foreground is very dark. 18% will allow the camera to make the exposure correct so that in the RAW workflow we can still see the sky and the foreground.
The White Balance While you can use the 18% Gray to do a white balance it is not something that we suggest as the results are balancing to the gray not to the neutral white.
White balancing can be done both in Camera and post shoot in third party editing software such as Photoshop, Lightroom, Aperture or Capture One for a few examples. White Balancing in camera gives you a better view on the LCD of how the images have been shot rather than risking a blue or yellow cast to the RAW data you are viewing in the camera. This can be applied to either a RAW workflow or a JPEG workflow in your software post shoot using the white balance eye dropper tool. White balancing in camera will allow you to spend less time editing when you ARE post processing.
Shooting in RAW allows much more room to work with your images post processing then what a user will have in JPEG. The difference can be very amazing when you white balance and the time you save will allow you more time to shoot – the main goal!