Wednesday, September 02, 2009

Tower Reflections

The exhibits at the festival are best seen at night. One feature that plays a prominent part in many of the displays at Ontario Place is water - of course this makes for an excellent opportunity for reflection shots.

1/125 f/4 ISO 800 24.0-105.0 mm @ 24 mm Canon EOS DIGITAL REBEL
Ontario Place,Toronto,Ontario

A recent podcast by Martin Bailey discussed Dynamic Range. Other than being a little loose with the distinction between Exposure Value (EV) and Dynamic range, Martin does a good job. I did a little bit further surfing on the topic and there is a lot of confusion out there. One of the big debates is whether there is a strict connection between dynamic range and the number of bits in the digital capture system of a camera. Although I understand how people could get confused about this, let me state that they are quite independent. Consider an analogy.

Suppose you have a stair case which rises 3 meters between the two floors. This would be the equivalent of the dynamic range. Suppose you could put in two different stair cases; one with 16 steps and another with 8 steps. It does not matter how many steps there are the height between floors is still the same. A different building might have floors which are 4 meters apart (wider dynamic range). You could still have 8 or 16 steps.

With digital cameras the sensors have different dynamic range capabilities some may cover 11 stops, others might cover 14 stops. If you shoot jpeg, you will cover that range with 8 bits per colour (256 steps). If you shoot RAW, it may be 12 or 14 bits per colour (4096 steps or 16,384). The more steps that cover the same range, the smooth the colour tones will be.

Finally what is the difference between EV and dynamic range? The Wikipedia entries are good reading if you want to understand more deeply. There is also some variance between strict definition and common practice.  I think a building analogy works well. Consider a tall building. The total height of the building would be like the EV range of the camera. But you can only climb one set of stairs at a time and that covers the height between floors. That would be the dynamic range of the sensor.  One significant shortcoming of the analogy is the with a sensor the dynamic range decreases as the ISO values increases (or at least that is the general case with most cameras today).
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