20 May, 2007
In the final part of my short guide to exposure, I bring the whole process together and examine the thought processes I went through in a number of real field situations.
I follow the same routine to evaluate the exposure for each image I make. In each case, I am looking to select one reference point to use as a base for metering – either a midpoint, a highlight or a shadow.
Here is the process:
- Identify a mid point exposure - either by
spot metering (most scenes) or using an
incident reading (macro or closer in scenes).
- Find the brightest point and check that it is in the range of the film or sensor. If it is not decide whether to
meter for the highlights ,
add a graduated filter or switch to a higher latitude film.
- Check where the shadows fall and decide if you want to meter for the shadows or not
- Make the final adjustments for filters and (on large format) bellows factor, if necessary
- Re check your exposure just prior to pressing the shutter (because light changes and our eye doesn’t always notice)
Here are some real examples to illustrate the process.
For the green fern, I used an incident reading to get an accurate exposure. Using a quick disk indicated that +1.3 stops was necessary to account for bellows factor.
'Rowan Tree Falls'
The primary risk in this scene was not retaining sufficient detail in the water. Having started with a spot meter reading on the grass , I checked the highlights. It was on the edge of the film (velvia), about +1.7 above the mid point. So I chose the water highlights as the reference point to be safe. (I metered from the highlights and added +1.7 stops.) In retrospect, this was a quite brave thing to do with this image. Running water like this can often trick the meter and a more conservative approach might be to add +1.5 or even slightly less.
'Dawn over Loch Cleat'
This scene was going to need a graduated filter to expose successfully for transparency film (Velvia). Comparing the midpoint (spot reading off some sunlit grass) and the highlights in the sky, a two stop grad placed the highlights within range of the film. Having positioned the filter, I waited until the right moment came. As soon as it did, I spot read off the sunlit grass on the mountain side (and double checked that a two stop grad was right) and exposed for that.
'Spotlight on Horcum'
This was an interesting case. Which grass should I meter off? One choice is to spot the bright sunlit grass and meter off that. The problem with this apporach is that the rest of the grass will be very dark, resulting in a rather underexposed looking image. Alternatively if one meters off the shadowed grass, the highlights will almost certainly blow. In this case, experienced judgement is needed to recognise that the right question is 'where to place the highlight?' I metered the brightest point of sunlit grass as a coloured highlight and placed it at +1. It will retain sufficient colour at this position to come out green but give the rest of the image chance to expose.
In this icicle scene, I was determined to retain shadow detail. I metered for the shadow area and reduced the exposure by -2.7 (for provia film).
'Bishop Wilton Tree'
In this final image, there was a lot going on. I polarised the image in order to darken the blue sky. I could then take this out of the equation. I had used a huge amount of front rise which would create light fall off. So I added a one stop soft graduated filter to compensate. I tested the various points on the tree and found that I could just about hold shadow detail if I metered for the sunlit bark at +1 and the sunlit green leaves at the top would fall close to a mid point. So I metered off the sunlit bark, added one stop to compensate for it being a highlight with colour, added +2 stops for the polariser and +1 for the graduated filter. I.e. metered for a highlight and added +4 stops.
© Jon Brock 2007 and 2010