Wednesday, 16 June 2010

Digital Photographic Practise 1: Exercise 9: Scene Dynamic Range

For the first shot in this exercise I chose a typical country scene in scene full sunshine.
The bright spot in the clouds was 1/1250 at  f/8 and ISO200. Although the hedgerow on the left looks relatively dark in  this image the meter read 1/30 at f/8, giving a total dynamic range of about 4.5 stops. This is well within the range of the camera, and a different treatment of the RAW reveals detail in the hedgerow at the expense of the overall effect of the picture. As with white balance and exposure, dynamic range can be manipulated to some degree to achieve a particular effect. I this case the contrasty result enhances the impression of bright sunshine.
Another shot taken in bright sunlight, this Bleeding Heart also has a relatively modest dynamic rangeP6126097
The white on the flower registers 1/640 at f8 (ISO200) while the dark shadow registers 1/50 – around 3.5 stops. This feels a little narrower than it looks – in particular the shadows are quite dense – and may reflect the fact that even the spot metered point is not sufficiently small to accurately measure the small proportion of the picture represented by the white of the flower or the deepest shadow areas.
Two pictures now of the same scene in slightly different lighting:
This one, with sunlight outside shows a range of 1/1600, f8, ISO 200 (in the sky) to 4 secs at f8 (in the shadow by the printer on the left. This is almost 13 stops - well outside the range of my camera although a barely acceptable image has been achieved by relying on the fact that we would expect some deep shadows in this kind of image (at the sacrifice of some detail) and the area of sky is sufficiently small that it is not too obtrusive . It is unlikely that this would make a good print however.
In this version, on the other hand, the weather is cloudy outside, a greater proportion of the interior light is coming from an unseen window to the right of the picture and the sun is not facing the camera position. The sky now measures 1/800 at f8 and the shadows around 2secs giving around 10.5 stops. This is still outside the range of the camera but it is certainly easier to use the image. This hints at two ways of controlling contrast – use of a more diffuse lighting source, and using extra lighting to fill the shadows.
Finally another outdoor shot in very flat cloudy evening light.DPP-Assignment-2_10
According to the camera meter this has a range of less than 2 stops: 1/25, f8, ISO200 (on the tree through the arch) to 1/80 (on the wire and woodwork.  This gave a rather dull image without enhancing the contrast in RAW development.
Thoughts on dynamic range
A couple of my thoughts on this issue:
  • anything with brightly lit cloud in the picture is likely to have high dynamic range
  • bright sunshine is not necessarily a problem unless there are well lit clouds in the sky
  • flat lighting and low contrast can be as challenging to a photographer as pictures with a high contrast.
  • low contrast pictures can be perked up in post processing if more contrast is required
  • high contrast pictures are more difficult to manage because the captures file has to sacrifice detail in either the shadows or the highlights. the former is generally a better solution.
  • counter-intuitively using flash, or additional lighting/reflectors can reduce contrast at the point of capture and give a more manageable file.

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