articles/Lighting/exposingfordigital-page2
by Dave Montizambert Published 01/10/2008
Another way to judge exposure that I think is rather clever is the 'Vincent O'Byrne method'. This method shown to me by my friend and colleague, Irish commercial photographer Vinnie O'Byrne, makes use of the highlight alert feature (see Image 02) on the LCD preview on the back of his camera, this feature is on most professional digital SLRs.
Vinnie takes an exposure or two of the scene in question, then looks at the image on the preview screen with the highlight alert turned on; the high-light alert function is generally found in the camera functions menu. When this function is turned on, any areas of the image that approach 255 levels of brightness will have a contrasting flashing overlay like the red highlighting in Image 02. In subsequent captures, Vinnie then decreases the exposure in thirds of a stop until the flashing overlay goes away. This puts the highlights exactly 1/3rd below burnout, maximizing all of the bit depth that the camera has to offer.
This method does require a little intelligence from you. You need to decide the bright tones in which you want to maintain detail, since not all images need detail in all bright tones. For example, a white backdrop that you wish to render as pure white needs to burn out and so we would ignore the highlight alert in these areas.
The great thing about Vinnie's method is that it does not rely on in-camera metering and so works for all types of lighting: daylight, tungsten, HMI, strobe/flash, etc; digital SLR in-camera meters cannot read exposure for images lit by strobe/flash - they are not flash meters. This flashing overlay method has a couple of drawbacks: it is calculated using the in-camera processing settings that are used to create JPEGs from the camera and so does not take in to account the full range of tone available in the RAW capture and it will not give you perfect exposure results for every image situation, nor will it allow you to accurately predict lighting ratios, but it will ensure a good yield of information that can be manipulated to suit, during RAW processing.
About 99% of my photography involves lighting; seldom am I recording existing lighting. For this reason I am a believer in hand-held metering, with a top-of-the-line flash meter for most photographic situations. When using a hand-held meter, the best way to ensure a correct exposure is to set the brightness of the subject via middle-grey, just like film. The two most common and effective metering methods are:
A) Take a reflective reading off a middle-grey card at the subject plane.
B) Use an incident meter with its back against the subject
plane and its white dome or disk pointed directly at the light source in question.
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