articles/Cameracraft/expstrat-page3

Exposure Strategies - part 3 of 1 2 3 4 5 6

by Mike McNamee Published 01/12/2013

Commentary

The bottom row contains the as-shot Macbeth Charts from a 7-frame bracket set at 1-stop increments. The Macbeth Chart usually fools the exposure meter of cameras and in this instance the 'correct' mid-tone exposure is 4/10 less than that judged by the camera. The top row shows the files from the bottom row after each has been individually adjusted in camera Raw to bring the 50% grey patch up to the required 121 RGB points (which is actually 51% Luminance but stay with us!). Visually you observe that as under exposure of the original is approached, the contrast of the corrected file is increased, as is the saturation. At the 3 stops over-exposed value (which remember is nearer 3 1/2 stops), the Chart is a real mess and the light skin-tone is completely un-recoverable. The contrast is now falling rather than increasing. The minimum verall error is reached at the zero and +1 brackets, in other words pulling the slightly over-exposed shot back has minimised the overall error. Either way,for the relatively modest contrast range of the Macbeth Chart there is a full stop of adjustment available without penalty to colour error. The noise reduces from the high values in the under-exposed shots but levels out and remains better at all over-exposed targets.

Calculating the Exact Mid-tone Exposure

With the luxury of time it is possible to establish the exposure which gives exactly 50% luminance for a 50% mid-grey. Here we have gone as far as using statistical analysis to predict the exposure value with some precision. It shows a 4/10 -stop error.

Please Note:
There is more than one page for this Article.
You are currently on page 3

• Exposure Strategies page 1
  
• Exposure Strategies page 2
  
• Exposure Strategies page 3
  
• Exposure Strategies page 4
  
• Exposure Strategies page 5
  
• Exposure Strategies page 6
  

Contact Mike McNamee

1st Published 01/12/2013
last update 21/07/2022 08:46:24

More Cameracraft Articles

There are 0 days to get ready for The Society of Photographers Convention and Trade Show at The Novotel London West, Hammersmith ...
which starts on Wednesday 15th January 2025