Metering light for color negative film
While most modern cameras have built in light meters many prefer to use external (hand held) ones for better control over exposure. There are two kinds of light meters today, incident meters and reflective meters. A spot meter is a reflective meter with a very narrow (preferably one degree) field of view.
Reflective light meters
You point a reflective meter towards your scene and it reads the light bounced off of (or emitted from) the objects in it. Because of this, reflective meters are influenced both by how much light there is in the scene and how reflective the subjects are. They are designed to make all objects appear average in brightness, equivalent to medium (18 percent) grey. Because of this they will suggest camera settings that will overexpose very dark subjects and underexpose very light subjects. In most instances, this often requires knowledge of how to adjust the suggested camera settings for a pleasantly exposed image. The meters built in to our cameras are of the reflective type.
Incident light meters
If you take a narrow reflective reading (spot reading) of an 18 percent grey card, you will get a correctly exposed image. While this could be considered the gold standard of light metering, the use of a grey card is often not practical. Fortunately, you will in most circumstances get an identical reading using an incident light meter instead1. This type of meter reads the amount of light illuminating the subject and ignores subject and background characteristics, such as reflective properties2. Subjects that appear lighter than middle grey to your eye will appear lighter in the finished image. Subjects that are darker than middle grey will appear darker3. The rest of this text will only deal with incident light metering, which is an excellent way to meter for use with color negative film, and often black and white film.
To use an incident light meter you simply place the white dome (which covers the light sensitive sensor) in the same light as your subject. In practical terms, you hold it near the subject, perpendicular to the ground and aim the dome towards the camera. In uneven light, such as a portrait in directional light, you have the artistic choice of what part of the scene you want to meter for; the highlight side of the face, the shadow side of the face, or holding right in between and get an average reading. If it is not possible to get the meter close to the object you can simply try to place the dome in the same kind of light as the subject is in, such as shading the dome with your hand to get a shadow reading for a scene further away4. Some incident light meters have a fix dome, some have a dome that slides to the side for reflective readings and some have a dome that can be retracted for a narrower field of view.
The Gossen Digiflash 2 in incident mode (left) and reflective mode (right).
The Sekonic L-478D, with bulb out (left) and bulb in (right).
Techniques for overexposing
There really is no perfect exposure value to hit when you meter a scene. Instead you have an exposure range to work with. If you place your exposure within that range you will be able to get a pleasant result from your digital or film development process. For digital this range is rather small (a stop or two, assuming you have a nice sensor and are shooting in RAW). With film, the range is small for slide film (around half a stop), wider for black and white (around two stops, depending on the stock) and very wide for color negative film (for some stock up to five stops). With film, this is called exposure latitude, and this makes life a lot easier for film photograpers.
The films ISO rating states the minimum exposure at which you will get a nice image. Underexposing film gives a negative lacking in information, producing crushed blacks and muddled colors. So, as opposed to digital, you need to error on the side of overexposure. More light (overexposure) gives a denser negative, rich in information to be used in the scanning or printing process. Overexposure also adds contrast, and sometimes saturation.
Most color negative film (with the exception of Kodak Ektar) needs somewhere between half a stop and three stops of overexposure, depending on the film stock and light properties. Fujicolor 400H, for example, is commonly overexposed one stop in full sun (high contrast light), two stops in backlight (medium contrast light) and three stops in totally flat light (low contrast light). There is more controversy as to how much overexposure Kodak Portra 160 and Kodak Portra 400 needs, which illustrates that much of this is an artistic choice5. As long as you keep your exposures within the range of your film stock you will get a nicely exposed image. You will however control the look of your image with how much you overexpose it.
There are a few different ways of achieving overexposure using an incident light meter. The techniques discussed below apply mostly to lower to medium contrast scenes, such as open shade. In high-contrast scenes, such as direct sun, it gets trickier6.
If you set the light meter to the ISO of your film and hold it in
If you set the light meter to the ISO of your film and hold it in front of the subject, perpendicular to the ground, with the dome out (not retracted) and pointed towards the camera, you get a technically correct exposure reading. If you meter a face half lit and half in shadow the white dome should also be half lit and half in shadow. This will give you a nice “average” reading of the light falling on your subject.
From the base reading in (1), you can simply add the desired amount of overexposure. If the meter says 1/1000s at f/2.8 you might set the camera to 1/250s at f/2.8 to overexpose the scene by two stops.
If you put the dome in the shaded part of a scene (for example under the chin) you will gain between 0.75 and 1.5 stops of overexposure as compared to (1). This is a technique favored by Johnny Patience4 and José Villa7, for instance.
If you retract the dome you will overexpose the scene by about 0.5 to 0.75 stops8 compared with (1). If you also hold the meter at an 45 degree angle towards the ground (away from the object and towards the camera) you will overexpose the scene by an additional 0.5 to 0.75 stops. By combining the two, you will overexpose your scene by a total of 1 to 1.5 stops, depending on the light and your surroundings 9. This is a technique used by Jonathan Canlas10.
- Any of these techniques can of course be combined with rating the film at a lower ISO, to start with a baseline amount of overexposure. José Villa, for example, rates Fujicolor 400H (an ISO 400 film) at ISO 200, to start with a one stop overexposure, before he meters for the shadows to add at least one additional stop of overexposure11.
Left: An averaged reading, with the bulb in front of the face. The distribution of light and shadow should be the same on the bulb as on the object you want to expose for. Right: a shadow reading. This will expose for the shadows, which means the highlights will be overexposed between one and three stops, depending on the contrast of the scene.
The “bulb in, angled 45 degrees down” approach.
Final words of comfort
All this being said, do not overthink this. Arguably successful photographers, such as José Villa, use a technically very simple approach. Experiment and find a systematic approach that works for you in the majority of light scenarios. Learn to identify problematic light, where you have to be more careful. Remember to always err on the side of overexposure when you shoot film and all will be well.
Even an incident light meter might get fooled if your subject is extremely light or dark. If you want to render details in those objects, you should decrease exposure by half a stop for light objects and increase exposure by half a stop for dark objects—the opposite of what you would do with a reflective reading. ↩
Erica and Christian of the UK Film Lab did a nice comparison of overexposing the Portras and Fuji 400H. Carmencita Film Lab did one too. ↩
But who wants to shoot in that light anyway? ↩
Villa J, Kent J. Fine Art Wedding Photography. Amphoto Books; 2011. It’s worth noting that Villa seems to mostly use reflective readings from the subjects shaded chin. The caucasian skin is lighter than middle gray, which means you usually need to overexpose the reflective reading by a stop to get correctly exposed image. So, if Villa rates his Fuji 400H at ISO 200, but then takes a reflective skin-reading, I would say he arrives at exposing at box speed. Interesting. ↩
Being half a sphere, the dome normally sees light in a 180 degree field of view. A retracted dome sees light with a narrower field of view, which for instance might be used to lessen the influence of a bright sky on the reading. ↩
The reflective properties of the ground and buildings around you will of course affect this. Green grass (having a luminance near middle grey) is pretty neutral, while snow reflects a lot of light back up towards the meter. ↩
Canlas J, Kalp K. Film Is Not Dead. New Riders; 2012. ↩
If you are to believe Villa’s book, he mostly uses his Contax to take a reflective reading of the skin of his subjects. Since caucasian skin tones are about one stop lighter than middle grey this would mean that Villa cancels out the stop of overexposure he added by rating Fuji 400H at ISO 200 and that he actually shoots at box speed. Interesting. ↩