Correct Exposure for Portraits
Two things are in favour in getting the correct exposure for portraits. Firstly, you really only need to worry about getting the correct exposure for the face. Secondly, as explained under films, negative film is far more forgiving than colour slide film if you make an error, especially if you overexpose a little.
Here are a number of techniques for getting the correct exposure. These are listed roughly in order of their accuracy, not in order of ease of application.
Incident light Reading
Using a separate hand-held exposure meter, attach the invercone or light diffuser over the cell. Place the meter as close as possible to the subject (eg 5cm from the subject's face). Point the invercone towards the camera. Take your reading. If there is a difference between the shadow and highlight side of the face, take a reading from both and average the results but lean towards the shadow reading. Transfer the meter readings to your camera settings in Manual mode.
Grey Card Reading
(You can buy a Kodak Grey Card pack from good camera shops. They cost about $25 to $30.) A Kodak Grey Card reflects 18% of all light falling on it. The reading should be identical to an Incident Light Reading and saves you spending $300 to $600 on a separate exposure meter.
Place the Kodak Grey as close to the subject as possible. Take your camera close to the grey card so that your entire viewfinder is filled with grey. Take a reading from
the same direction that you will take the photograph. Use these readings on your camera in Manual mode. Note: When you move back to the position from which you take the shots and remove the grey card, your camera will indicate a different exposure. Ignore these readings. You have already metered the correct exposure.
Matrix TTL Metering
Most modern SLR cameras have spot and matrix metering systems or variations on these. Matrix metering means the camera designer has designated certain zones within the viewing frame and each zone influences the exposure reading by a different percentage. Eg the centre zone may occupy only 10% of the space but influence 75% of the exposure.
With matrix metering set, take the reading in either Aperture Priority Mode or Portrait Mode. The camera will automatically give you an exposure that is near to correct.
While not as accurate as the first two methods Matrix TTL is quicker and more versatile. Always allow a margin for error by being generous with exposure. Eg rate your 400 ISO film at 320 ISO.
A really great habit to get into for ANY photography is to guess the exposure in your head before you take any readings whatsoever. After a while you will become amazingly accurate (you'll guess to within one stop!). This habit has two great benefits.. Firstly, you won't make a silly error by blindly following the technology when something is wrong (eg the incorrect ISO). Secondly, when your metering system breaks down in downtown Kathmandu you will still achieve great exposures.
Meter off the Grass
This technique is quite similar to the Grey Card reading. Green grass also has about 18% reflectance - the same as a Grey Card. Using you camera in Manual Mode, take a reading off the green grass and leave that setting when you point the camera at the subject. Ignore the new readings!
Meter off Your Hand
With your camera set to Manual Mode, point your camera to your hand and take a reading. Now adjust your reading by opening up the aprture by half a stop to one stop. As hand colour and density varies, this takes some practice and experimentation.
Spot Meter the Highlight
Take a spot reading off the highlight (eg white hat or dress) in your picture area and open by two stops. Once again, this is done in Manual mode.
The Famous f16 Rule!! This is really good for landscapes but not quite as useful for portraits because portrait photographers don't use f16 very often. But here's how it works - In bright, sunny conditions, you transfer your ISO speed to your Shutter Speed and use an aperture of f16. You will achieve close to perfect exposure. Example: You're photographing children at the beach in full sun and using 200 ISO film. Set the camera to f16. Transfer 200 ISO to shutter speed - the closest speed is 1/250 second. Exposure is therefore 1/250 @ f16. Better still, the portrait photographer transposes that and says 1/250 @ f16 is identical to 1/2000 @ f5.6, which gives less camera shake and a shallower depth of field. Use 1/2000 @ f5.6.