Last week’s meeting – Smart Shooting Part 2 – From the Ordinary to the extraordinary – Bob Brind-Surch
This was a fascinating talk even though it was somewhat heavy on numbers and the science. Essentially Bob was explaining the difference between an exposure strategy for film and digital. This was summed up in the differing sage advice of film pioneer Ansel Adam ‘expose for the shadows and developed for the highlights’ and creator of Photoshop Thomas Knoll’s digital version ‘expose for the highlights and process for the shadows’.
Bob explained in detail that the tones a digital sensor captures (the data) is very heavily skewed to the highlights. This is because each ‘stop’ is half or twice the magnitude of the adjacent ‘stop’. Across a typical 10 stop graduation of tones from black to white the amount of data in the darkest shadows is 16 while at the opposite end in the highlights the data is 8192.
This issue becomes important when shooting at ‘noisy’ high ISO settings. Bob showed the example of a shot of a gorilla which was shot ‘’correctly’ exposed compared with the same subject shot at a higher ISO but the same aperture and shutter settings – overexposed by a stop. The ‘correctly’ exposed shot had significant noise in the shadows while the over exposed shot, once it was darkened in editing software, had all the details in the shadows and no noise.
The way Bob suggests you do this is not to look at the image at the display back of the camera (chimping) but to look at the histogram and make sure you are ‘exposing to the right’. The key is over exposure (his rule of thumb is by two-thirds of a stop) and make sure that the righthand side of the histogram is as close to the extreme of the right side. If it goes too far to the right it will blow out the highlights. He also said you can do some ‘blinking’ on your display as well to see if the highlights are blowing out.
This method may not be for everybody and can be risky if you overexpose too much and blow those highlights, but well worth being part of your tool kit when shooting at a high ISO setting.