Tuesday, November 30, 2010

Ex. 8 Camera Dynamic Range

This was interesting, many challenges and some useful learning.  The first trick was to understand exactly what the exercise wanted, took a couple of reads to understand the goal fully.  The next challenge was going to be the weather, however, for a change I had a stroke of luck.  Two days ago we had 10cm of snow and then this morning the sun came out.  Ideal conditions for this exercise, the snow is about the most reflective substance I could have used.  As suggested I took a photo of the front door of a house with an open door showing a shadowy interior.  I positioned a sheet of A3 card as suggested, although this was not the brightest thing in the frame.

For the exercise I have used a hand held spot meter to evaluate the relative brightness (one of my favorite tools), but first started by taking an incident light reading.  This gave me 1/1000s at f/4 and ISO100.  I took a photo with these settings, but got a highlight clipping warning, so captured the following at 1/1500s, slightly underexposing to avoid the snow blowing out

I then walked around the scene and using the spot meter obtained the following exposures (with a constant f/4).  In fact inside the house in the very darkest area the reading was 1.6s. So a very high contrast scene - in effect 13 stops.

In Lightroom I have zoomed in on the darkest area of the image, i.e. everything inside the door frame and then increased the fill light to check what detail has been

The darkest area that is resolvable is the picture frame in the left hand side of the image above.  This metered at 1/13.  There is some other detail in darker areas, but it is not resolvable as anything recognizable.

Doing the Maths:

2 ^ x = (the highest resolvable shutter speed) / (the lowest resolvable shutter speed)

where x is the dynamic range, solving

x = log(high/low) / log 2 = log (8000/13) / Log(2) = 9.3

So not a bad result, the 5D2 has a dynamic range of around 9 stops.  This gives me confidence that if I expose for the highlights, I will be able to pull detail from the shadows.

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