I set the Camera to ISO 50 and carried out the tests as required by the Exercise notes. I used the Zoom facility to 'capture' the white card and the dark shadows in the top left hand corner of the open door, the top right hand corner and the shadow in the bottom left quarter of the opening adjacent to the light brown of what is a paste table. The image was zoomed to 100% in Camera RAW software.
The f stop required to achieve a white point of approximately 255 was f4.5. (Actual result was R 253; G 253; and B 251). As suggested I increased the exposure until the 'shadows were visible and the presence of noise could be detected. The point at which it was difficult to distinguish between noise and the detail in the shadows varied in the three different areas but the equivalent of an f stop of f18 seemed to be about right. As indicated in the notes it was not easy to make this judgement. These results suggest that my camera has a dynamic range of 12 stops.
Even after doing the exercise I remain uncertain as to what use I can put this information to in a practical way. Faced with a shot that has a wide dynamic range I make an assessment of where the important information lies and set the camera to get the best result for this area. If this is not possible or desirable I do one of two things; either I will bracket the shots and combine in photoshop or take two separate shots of the shadows and the highlights and combine again in photoshop. Experience tells me that this procedure will cover the vast majority of the images I take.
Lessons learnt - I now know the apparent dynamic range of my camera and I now have a good idea why bracketing the exposure of the shots gives a high percentage of shots that cover the dynamic range of the taken image. Once again I learnt more about my camera in that I now know that the lowest ISO can be set at 50.
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