Friday, September 9, 2011

P11: the colour of daylight

One of those projects with a lot of reading, but without an appreciable element of photography.  I understand the concept of colour temperature and often carry an 18% grey card in my bag to enable me to establish White Balance (WB) when shooting something of importance to me.  Completion of over 600 scuba dives with a camera has also enforced an understanding of WB and how different scenes can engender a colour cast.  As I only shoot  Digital I have no real use for colour filters, although I have experimented with them in B&W work, but found I can do as much if not more in software.

I generally find that with the more recent DSLRs such as my 5D2 the camera does an excellent job of working out the correct colour temperature, especially when I compare back to the 20D my first DSLR.  Subsequently I tend not to worry very greatly about managing colour at the time of shooting, although I did find in Assignment 2 that I had challenges balancing the colour between photographs taken on different days under slightly varying lighting conditions.

Moving onto the discussion of contrast and the suggested exercises on pages 70 and 71, I thought it would be interesting to see what the differences really were between incident and reflected meter readings from different surfaces.  I have a Sekonic L-758DR meter that has both incident and spot metering capabilities, another tool I frequently carry when doing more deliberate planned work or wherever a bride might be present...

It is 23 degrees outside with a 3pm sun on a September day - sunrise was at 6:40 and sunset today will be at 19:50, so the sun is still pretty high and bright. I placed a bench in a sunny part of the garden; on it I placed a piece of black card, white card, and some black felt.  I have no velvet, so felt had to do.  Setting the meter at f/8 and ISO100 I obtained the following readings:
  1. Incident Light (no reflections): 1/400s
  2. Black Card, reflective spot reading: 1/320s (about half a stop down)
  3. White Card, reflective spot reading: 1/2500s (2.5 stops brighter)
  4. Black felt, reflective spot reading: 1/80s (2.5 stops darker)
Interesting, the black card doesn't modify the light very much, however, the white card is essentially becoming a specular reflection of the sun.  The felt was slightly reflective when placed in the sun, so not completely absorbent, but not too bad.

We live in a town house, a 3 story terraced terrace in a row of 12 sandwiched between low rise apartment blocks typical of Munich!  Directly in front of the house and due East is a 5 story block of flats painted white, a great reflector of light.  In the evening it is warmer to sit on the east side of the house than the west because of this reflection.  Just taking my meter to the front of the house increased the needed shutter speed to 1/500s, moving closer to the wall upped it to 1/640s, so essentially an extra half a stop of brightness.

The other learning here and a key one was reinforcement of the oft quoted SUNNY 16 rule, i.e. that on a sunny day with the camera set at f/16 the exposure should be the reciprocal of the ISO number.  In my case I metered 1/400s at f/8, which is equivalent to 1/100s at f/16, at ISO 100.

I am quite comfortable using exposure compensation, appreciating the fact that the reflective meter in the camera struggles to deal with large expanses of either very dark or very light materials.  Having completed 2 weddings this summer, both with brides in a very traditional white, avoiding photographing a grey bride was very uppermost in my mind.  For formal shots I use the meter to accurately set the exposure, for the less formal stuff, I tend to find my camera does a pretty good job even with a white dress.  Lightroom can help quite a bit and I am happy increasing or decreasing exposure by up to one stop, and more if processing to B&W.  Better to get it right in camera, but in a Digital workflow, capture is simply the first step in a process that ends with a printed photograph.

Key Learning:

  1. Reflected light adds to incident light and can substantially modify the exposure
  2. White objects can act as specular sources, so take care
  3. Sunny 16 rule actually works:)

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