Pixiq

High Key images have a low contrast and insignificant shadows. From talking to people who attend my photo workshops, metering tricky subjects – notably high and low key ones – is invariably tackled by shooting first before chimping the monitor and adjusting the exposure. Compared with film, this does not cost anything, but it means you have only a slim chance of an action shot being the correctly exposed one. Another method is to auto-bracket; yet high key subjects will require an increase in exposure rather than a decrease on the TTL metered reading.

It is far better to aim to capture correctly exposed outdoor high key images first time round.

Digital cameras are great.  However you only have to meter a frame-filling green lawn and then a frame-filling white board or sheet (in the same light with same lens at the same focal length) to appreciate metering light reflected from different toned subjects will produce quite different exposures. In this case, the result will be an underexposed gray sheet (or what I call the gray snow syndrome).

For much of the time, the camera's auto metering modes – P (Programmed auto), Shutter Priority (S), or Aperture Priority (A) – will work fine. However, because the camera meters light reflected from a subject and attempts to make everything a mid gray tone, it gets it wrong with bright (high key) or dark toned (low key)subjects.

The first step in the right direction is to learn to assess rapidly whether what you have selected in the frame is a mid gray / average tone or not. Green grass happens to be a good average tone as are many plant leaves (but not silver or yellow ones). Look at the composition and quickly judge how much of the screen is brighter than average. For example, any black and white subject that fills a frame with the white parts covering the same amount of area as the black parts (such as a giant panda face), is easy because the whites cancel out the blacks and so an average matrix meter reading works just fine.

 High key subjects however – such as a white swan, a polar bear on a snowy expanse or a white flower filling the frame lit by soft light without strong shadows –  are much brighter than green grass. So if you go with an unadjusted TTL camera reading without making an adjustment, the shot will appear underexposed i.e. a white flower or snow will look drab and appear gray.  However, when correctly exposed, their histograms will have a full set of tones, some mid and some black present but with a high peak over to the far right.

For many years, when not actually shooting, I will constantly spot-meter rocks and plants to compare the exposure with what I know is an average tone, so I can then gauge pretty accurately when something is brighter or darker than average. With a white or pastel toned flower, I manually meter off a matt green leaf nearby the flower (it does not even have to be the same plant, but it does need to be lit in the same way) and go with that exposure. The only times I need to readjust the exposure is if the sun suddenly goes behind a cloud or reappears from behind one.  

With practice, you will be able to look at a white flower filling half the frame surrounded by green leaves and either manually spot meter off a green leaf or simply look at the proportion of white in the frame and decide the exposure needs to be increased by ⅔-1 stop. Whereas a larger area of white flower and less green, will need more adjustment– some 1⅓ stops; and an all white scene will need to opened up 1⅔ or even 2 stops. (the aperture does not always have to be opened up, selecting a slower shutter speed will have the same effect or simply increasing the ISO).

How to meter

There are several options for getting a correct exposure with a high key subject.

1) Manually spot meter off a known average tone, such as a matt green leaf. Without any green leaves or grass in sight, place a gray card beside a plant emerging from white sand or snow and manually meter off the card.  Go with the manual average-toned reading.

2) If using P, S or A Priority modes, use the AE lock to hold the exposure before moving the camera to recomposes with the high key subject for just one shot. If you want to repeat it you have to use the AE lock again.

3) A gray card is clearly not practical for polar bears – or any wildlife for that matter – but if the sun is shining, manually meter off a shadow cast onto snow or the shadow side of a polar bear's flank and go with this exposure. Alternatively, if using a P, S or A exposure mode choose center-weighted or spot metering. If using center weighted metering, select the center focus area with the multi-selector and use the AE lock to hold that exposure for each shot. If you want to repeat it you have to use the AE lock again.

4)  Use a hand-held light meter to take an incident light reading of the light falling on the subject, by pointing the meter towards the camera with the white diffusion cone in place. Set the exposure manually using the correct combination of shutter speed and aperture given on the light meter.

5) To over-ride the automated camera reading, use the exposure compensation (need to use a + value to increase the exposure to compensate for a white rose or snow). Take a shot, check the monitor and make any further adjustments necessary. I don’ t use this because I find it all too easy to forget to reset the exposure compensation back to 0.

With brightly lit scenes, be sure to switch on the highlight clipping display—it takes no time at all to check if highlights are flashing due to overexposure.

See also my Pixiq post http://www.pixiq.com/article/harp-seal-pups-in-ice-cradles