Sunday, 23 September 2012

Exercise 27 : Measuring exposure

This next element of the course looks at outdoor light and how to manipulate it and use lighting conditions appropriate for different subjects.  The emphasis is on bringing texture and atmosphere to the photographs. The basic principle at work here is to be able to isolate the lighting from the other compositional elements that make an image.  Hunter et al (2012) is the recommended OCA text for the Light projects and I will also be making use of Arena (2009) for work with flash (I think the Speedliter’s Handbook is superb for its lighting diagrams as well for its guidance on the Canon flash systems) and the Strobist Blog.  I will also be exploring the use of light by other photographers and artists as I go along.

The first part of this exercise required 4-6 photos to be taken that were deliberately lighter or darker than the average.  My first shot is of a Dahlia flower was taken in brilliant sunshine which made the flower highlights burn out and the background greenery look extremely vivid and distracting.  I took this image with an exposure compensation of -1.5EV which controlled the highlights, toned down the background and introduced rich colour and texture to the flower.
Dahlia  -1.5EV
The second shot was taken with the light streaming in through the kitchen window and the camera set on evaluative metering made the scene very bright and with a midday sort of feel to it (which it was) and with the outside almost bleached out.  By actually exposing for outside the window at -2EV I was able to show the outside correctly exposed and create a dawn/dusk light feeling to the interior.

Kitchen  -2EV
The next photograph was taken by shooting directly into the sun over a local lake.  This was actually taken in mid-afternoon and was an intensely bright scene with the highlights from both the sun and its reflection completely blown and the remainder of the sky a misty blue.  Underexposing by 2 stops changed the scene completely and made the sky detail visible and threw the trees on the far bank into silhouette – absolutely nothing like the scene I was looking at or which the camera recorded as ‘correct’.
Lake  -2EV
My final shot featured a local lake just as the sun was setting.  Apart from the light just catching the trees in the distance, this was a very dark scene, so overexposure by 1.5EV introduced some detail into the foreground although consequently lost detail in the sky.  Obviously it would have been possible to recover sky detail by either appropriate use of graduated filters or in post-processing if it was required.
Lake  +1.5EV
The second requirement of this exercise was to produce five bracketed exposures (-1, -.5, 0, +0.5 and +1 EV) of each of six subjects and then comment on whether the 0 (average) value as calculated by the cameras auto system was indeed the best image, or whether the lower or higher exposures were to be preferred.  I don’t plan to blog all 30 images although I did take and examine the full range required.  All images were unaltered by any form of post-processing.
The first set of images here are of a local building photographed at midday on a cloudy but quite bright day.  All images were taken at a focal length of 105mm and f /8 and ISO400.  The first two images at -1 and -0.5EV were very dark as far as the building and foreground were concerned, but both brought out the cloud details in the sky.  The images at +0.5 and +1EV were better at bringing out the details of the building but lost the sky detail, whereas the cameras auto setting at 0EV was probably the best overall image.  If I was doing this ‘for real’ I would have shot at +0.5EV and then used the gradient tool in Lightroom 4.1 to recapture the sky detail.
Building  -1EV
Building  -0.5EV
Building 0
Building  +0.5EV
Building  +1EV
The second series of images is skip full of reclaimed metal and I liked the large range of light and dark areas as well as the colours.  The minus EV values appeared too dark as did the cameras auto effort.  +0.5EV gave the best balance of detail in the metal as well as giving some definition to the shadow areas.  +1EV was too bright for the highlight areas of the image.

Metal  -1EV

Metal -0.5EV

Metal 0

Metal  +0.5EV

Metal  +1EV

The third set of images I will actually post here are of a white house with deep shadows in the background trees so I could explore the influence of exposure value on well-lit white areas and poorly lit shadows.  -0.5 and -1EV again retained details in the sky and the -1EV exposure suggested an image taken early in the day with its emphasis on deeper shadows, especially on the front of the house.  The positive exposure compensation values certainly delivered more detail from the shadow in the trees, but the detail in the white paintwork of the house has disappeared along with the shadows which gave some structure to the image; they also lose the sky detail.  Overall I think that the image taken at 0EV offered the best compromise between lights and darks.

House  -1EV

House  -0.5EV

House  0

House  +0.5EV

House  +1EV

My final shot was of a view across the lake again, this time with the sun setting over to the left of the frame.  Shadow detail of the trees was very closed at all exposures other than that taken at +1EV which opened up the shadows and additionally brought some feature to the water and geese in the foreground.
Lake  -1EV

Lake  -0.5EV

Lake  0

Lake  +0.5EV

Lake  +1EV

The process of bracketing exposures is a common practice and one I have routinely employed when I have been shooting a subject that allows the time.  For my wildlife photography I have generally ‘exposed to the right’ of the histogram as much as possible without blowing the highlights, as in this region the signal to noise ratio is far greater and the level of information recorded in the image far higher.  However, it is sometimes necessary to adjust exposures to achieve a certain atmosphere in an image, either in the camera or in post-production.
This was an interesting exercise and reinforced the importance of exposure compensation as a route to changing an image.

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