24 Jan 2011

Into the Light

My Tutor advises me that it will take him a while to get to my Assignment so in the mean time I am starting to read Part 4 - Light.  In preparation I am studying from a few of my favourite photo books looking for information and background on this huge subject. I don't expect to get much from Tom Ang's Digital Photographer's Handbook as he only touches on each subject in a wide field covered by the book.  John Hedgecoe covers a bit more in his very detailed book The Photographer's Handbook and I do like the amount that John covers, leaving very few stones unturned.  However, I expect to get the most inspiration from Light, Science and Magic by Fil Hunter, Steven Bever and Paul Fuqua.

Of course our OCA study notes will by the backbone of my study materiel as it leads me into the first Exercise, Measuring Exposure.  To make sure that I fully understand how my camera measures light I have been studying my manual again.  My Canon EOS 5D and 5D II have the same metering systems which allow four types of light measuring.

The most sophisticated is the Evaluative metering mode which is an all round metering mode suitable for portraits and even back lit subjects.  This is a type of matrix metering which weighs the intensity of the light from all round the subject and using complicated algorithms, comes up with a light setting that limits the amount of blown and dark areas whilst concentrating on the subject which is assumed to be under the focus point used.  In almost all but the most difficult lighting conditions, this setting works very well.

The camera has 3 other types of metering.  Partial metering which covers about 8% around the centre of the viewfinder area; Spot metering which covers only 3.5% of the viewfinder area and Centre-weighted average metering which is weighted at the centre of the viewfinder but averaged for the entire scene.

Other metering controls allow a quick selection of exposure compensation by stopping up or down from the metered value by up to 2 stops.  In addition an automatic Exposure Bracketing setting is available for up to 2 stops either side of the metered value.  Finally, an exposure lock feature allows the metered value to be frozen and used when a subject is re-framed to a brighter or darker value.

Once a photograph has been taken, the monitor can produce a histogram of the light distribution in the image and illustrate blown highlights on the image thumbnail by marking the areas with a flashing outline. The camera uses between 10% & 18% of reflected light as its base exposure level.  Any object that reflects more than this will fool the camera into underexposure and visa versa.  This is why the photograph of a piece of white paper will often look grey.

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