How To Set Exposure With Your Camera

To set accurate exposure, photographers use a mid-grey card. One way of using such a card is to take an exposure reading from the card in a test shot of the scene. Or by having the card present in the actual shot, taking a meter reading from it, then cropping out the card from the final photograph.

Mid-grey is 18 per cent grey because on prints the half-way point between black and white reflects 18 per cent of the light. For specific reasons, light meters built into cameras are calibrated such that the average scene reflects about 12 per cent of the light. This is a half-stop difference.

This can be understood if the illumination of the mid-grey card is reflected at an angle of 45 degrees then the light meter will record a little bit under 13 per cent, so there is no need to compensate for that extra half-stop.

A good commercial mid-grey card reflects the same ratio of all colours of the spectrum, has neutral reflectance under a wide range of lighting conditions, such as tungsten, fluorescent, shade, etc, and can be carried in your camera bag.

You don’t have to get hold of a mid-grey card however, because it is probably more important to set the midtone point of a scene to a tonal value that you prefer. There is no such thing as correct exposure, only incorrect exposure - which will be clearly obvious.

With a bit of practice, you will easily find parts of the scene that are reflecting light at approximately mid-grey. From that you simply take a spot-meter reading. Do not use other forms of metering, such as matrix/multi-segment or centre-weighted metering modes, because these may not be accurate enough. Spot metering measures only a small area - the point which to you looks like mid-grey.

Chris Smith gives photography tips in his ezine that you can get every week for no cost. He has also put together a complementary report for you called ‘How To Master White Balance’, which helps you solve any white balance problems. To download it instantly and to obtain the ezine please visit: photography-expert.com