EXPOSURE

One of the biggest problems new photographers face is trying to determine the proper exposure of a scene. The problem? Your eyes can easily look at a scene, and see detail in a tremendous range of light, from dim shadows to bright highlights. In photographic terms, our eyes have more than 10-stops of "dynamic range" able to see details in dark black shadows and in the brightest whites of highlights. (See PDF example.)

Film and digital imagers aren’t as advanced.

Color negative film gives you a dynamic range of about seven stops, from the pure white of highlights to the blackest of shadows. Negative film also has a great deal of latitude: room for exposure mistakes. Generally speaking, you can overexpose medium speed negative film by two stops, without too much of a problem, and underexpose by a stop.

Shooting slides

Slide (also called transparency or 'chrome) films give you five stops of dynamic range. With transparency films, the more exposure, the lighter the image gets, so it is always best to underexpose. But beware, you have to be exacting with exposure. Overexpose by more than half a stop, and you will eliminate all detail in your highlights.

Black and white negative film:

When used by a master like Ansel Adams, this is the medium with the most dynamic range – able to record up to 10 stops of exposure. Adams used a precise metering technique called the “Zone system” and a spot meter to carefully measure the highlight and shadow details in his scene. A less demanding practice “expose for shadows and develop for highlights”, gives you eight stops of detail.

Digital camera exposure:

Digital cameras give you a range of six stops. They can be very unforgiving to over and underexposure, giving you “blown” or detail-less highlights with just half a stop of overexposure and shadows that are banded (instead of having smooth gradations) with more than one stop of underexposure.

If your digital camera displays histograms, use this and not the LCD to judge exposure. The histogram is a graph, which shows exposure levels from 0 (black) on the left to 255 (pure white) on the right.

“Expose to the right” of histograms, making sure you . Shoot RAW files if possible (see Digital notes for more details) .

Prints: When printed on matte paper, the dynamic range can drop to 5.5 stops, but custom printers can take advantage of the entire range of detail in the other stops.

Rules of thumb:

Properly expose your film and you will have printable details in the shadows and highlights. But it is usually best to overexpose color negative film by one stop. Color saturation and contrast will increase.

Overexpose too much and your highlights will be “blown out” with no detail.

Underexpose your film and your shadows will have no detail.

The midtones will be “muddy”.

It is best to err on the overexposure side with negatives and to underexpose with slide film.

LIGHT METER

Most SLR cameras have a built-in reflected-exposure light meter to help you determine proper exposure. Light reflects off subjects and into your camera’s lens and the meter senses the brightness of the scene to determine the “proper” exposure. Most meters are calibrated to 18% grey – the same reflectance as grass or blue skies at noon.

The problem is that the light meter has no way of determining what the brightness of your subject really is.

Say, for example, it has snowed. You go outside with your two dogs, one white and one black. The white dog is playing in the snow, you point the camera, it makes a reading of the light reflected off the scene and sets the exposure. SNAP. You spin around and see your black dog sunning on the paved, freshly shoveled driveway. SNAP.

You race to the lab, and an hour later, you are surprised to see that both scenes – and both dogs – are the same color of grey. Eighteen per cent grey. Your meter didn’t know what you were photographing. It guessed. And sometimes it guesses wrong. Instead of going to mental “auto” mode, think about what you are photographing. If it is a bright day, the reading should be within a stop of the “sunny 16” rule (proper exposure in bright sun is f16 @ 1/ISO)

When you meter a scene that is white, your camera will tend to under expose, so it’s best to take a meter reading and open up (increase) the exposure by 1.5 stops. Similarly, your meter will it overexpose dark scenes, so stop down (reduce the amount of light) by one stop.

And think about what is the most important thing in the scene. Is it better to have detail in a groom’s tuxedo or the bride’s gown?

Should I expose for the highlights or shadows.

TYPES OF REFLECTED METERS

Centre-weighted averaging: A reflected reading based on a midsection of your frame. Based on 13% grey reflectance of your subject. This is the standard meter on older cameras.

Matrix metering: In more advanced cameras, a computer reads from dozens of segments of the frame and determines the exposure. Slightly more advanced, but still far from foolproof.

Spot metering: Measures reflected light from a tiny area in the centre of the viewfinder. One easy way to verify your exposure is to take a reading of the scene, then go in tight to your subject and meter again. Also, grass is mid grey, and a perfect thing to verify exposure with. Some cameras have an “exposure lock” button to help with this technique.

INCIDENT METERS: A handheld meter that measures the light falling on a subject.

FIVE FINGERED METER: The cheapest, most accurate way to verify exposure is to hold up the palm of your hand, making sure it is catching the same light as your subject, move your camera close (without blocking the light) and meter off of it. Open up one stop, and you will have a properly exposed image.

ISO

Your light meter is designed to determine how bright the light is, in relation to the light sensitiivity of the film loaded in your camera. On newer automated cameras, the ISO is automatically changed when you change film. On manual cameras, you must adjust the ISO (or film speed) yourself.

THE LAB

No matter how good your exposure, most people have to trust the end result to the lab.

Machines that make 4x6 prints at one-hour labs also have meters that tell them how dark to print the film, and what color to print the film. And at the machines is an operator who may, or may not be very skilled.

It is not uncommon to have wild swings in color, especially in prints that have no reference point – like a face – which the operator would be able to judge color.

The nice thing about negative film is that it can be reprinted. For larger prints especially, a good lab will be able to correct color balances and densities. Assignment: Find a subject that interests you and shoot a roll of film, paying attention to aperture, shutter speed and exposure. Make sure your highlights and shadows are less than seven stops apart. Bracket your exposure in full stops - one stop over, normal and one stop underexposed.