Sunday, 30 September 2012

Exercise 29 : Judging colour temperature (1)

The requirement here is for a moveable subject to be photographed under midday sun, midday shade and finally when the sun is close to the horizon; the camera white balance needed to be set to ‘daylight’ rather than auto.  Firstly, I need to find some sun …and a willing volunteer as I wanted to do this with a face.

Midday sun is colourless or ‘white’ and light becomes coloured when some part of the spectrum is missing.  As the sun sets the colour of the light becomes yellow, orange and then (sometimes) red as the light is scattered by atmospheric particles and the distance the light travels from source to observer at dawn and dusk is further, therefore increasing the opportunity for scattering.  The shorter blue wavelengths get scatted more, so the remaining orange and red are therefore visible to the eye.  In the shade on a sunny day the observed light comes from the blue part of the spectrum.  So to the images …
Full midday sunlight
Midday shade
Sun close to horizon
My recollection at the time of shooting was that there was little difference between the colours of the images and that intensity of lighting was the only real difference between them – the eye compensates wonderfully well.  However, as can be seen from the photographs, the fairly neutral lighting of the sunlight version was replaced by a distinct blue/green cast (well, it is in the original – I have no idea what blogger will do to it via Picasa !) which is due to the light reflected from the sky.  The third image, which was lit by the late afternoon sun not long before it dipped below the horizon, has picked up the warmer orange tones from the last of the light and is by far the most pleasing image of the three I found.  By way of measuring the differences in exposure of the images, and no changes were made to the camera settings, the full sun version had a shutter speed of 1/1500sec, the shade of 1/90sec and the evening horizontally lit version had a shutter speed of 1/500sec.  The difference between the sunlit and shade versions was interesting as they were taken only forty seconds and two yards apart, and I would not have predicted such an extreme difference based on my memory of the time I took the images.

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