Metering for Film vs. Digital
Shooting film is a challenging process for many new photographers, especially those used to the instant feedback of digital cameras. Film, however, is a bit more mysterious. The complete lack of feedback from film, plus multiple film stocks (which all respond differently to light) adds to the complexity. Properly exposing color or black and white negative films requires a metering technique that is the opposite of exposing for a positive image. Permit me to explain.
Your camera’s built-in reflective light meter is very accurate. It evaluates the light reflecting from the entire scene, back toward the camera. This metering process is fine for digital, where our goal is avoiding overexposure (blown-out highlights). Your film camera’s matrix or evaluative meter is also an excellent tool for exposing transparency film (which is a positive image). Again, as with pixels, the goal is to avoid any overexposure.
Exposing for Negative Film
Properly exposing negative film requires a completely opposite approach. Whilst negative film has tremendous latitude, proper exposure is still important for consistent results. Rather than using a meter that evaluates the amount of light reflecting from the subject, we can benefit from a meter that can measure the amount of light falling upon our subject. We want to allow enough light to pass through the aperture and shutter of our camera to properly expose for highlights, mid-tones, and shadows. This allows film density to build and prevents underexposure. Failure to allow enough light to reach the film can result in muddy, underexposed negatives and poor quality prints.
The Problem with Reflected Light Meters
Light meters come in many forms, the two most important types being reflected and incident. The reflected light meter reads the amount of light bouncing off of your subject. They can be in-camera or handheld. These meters “see” very broadly or very narrowly. Terms like “center-weighted” or “spot meter” help you understand the pattern or angle a reflected meter accepts. However, a handheld meter is similar to your in-camera meter, in that it has no idea what it is being pointed at, but bases its analysis on returning 18% or a middle grey-based exposure.
Therefore, the photographer must always interpret the reading given by a reflected meter based on what is actually in the picture. Is your subject a bride in front of a wedding cake on a table draped with a white cloth? Or is your subject a coal worker, fresh out of the mine, against a dark brick wall? Neither of these subjects is average, and would easily fool an in-camera or reflected handheld meter, causing gross under or overexposure respectively.
The Beauty of the Incident Light Meter
An incident meter reads the amount of light falling upon the subject. Therefore they are much harder to fool. They may be outfitted with a half-dome spherical sensor or a flat disk. In practice, the dome is more useful for taking general readings of three-dimensional subject matter, like a face. The flat disk is more useful for flat copy work or by more experienced users for analyzing lighting ratios when using artificial lights. For live subject matter, lit by ambient light, a single reading, with the dome facing the camera, will give an accurate reading. Due to the latitude of negative film, there is usually enough exposure with this general reading to develop good film density in shadow areas.
So, how do we use an incident light meter? For portraiture, the meter is usually held under the subject’s chin. This will yield an average 18% reading, regardless of the subject. Is your subject backlit or in an abnormally bright location like a ski slope or beach? No problem. The dome of your meter is reading the amount of light falling upon the face of your subject. Simply transfer the reading to your camera and shoot away. Be careful not to shade the subject with your body to unduly influence the reading.
Rating Film vs. Box Speed
Have you ever wondered what people are talking about when they say they “rate” their film? In a nutshell, they are using experience to compensate for various factors, often when using a reflected light meter. With a correctly used incident meter, this practice can largely be avoided. The film speed or ISO rating of your film is very scientifically determined by the manufacturer, so by exposing it correctly, its box speed should yield good, consistent results.
Many factors contribute to the density of your negatives. Rating your film at a speed fractionally slower than box speed (setting your meter for 200 ISO, vs. box speed of 400) takes further advantage of the latitude of negative film and can, therefore, give a bit of a buffer to help reduce the chance of underexposed areas of a negative.
In the past, judging film exposure was fairly straight forward. When a contact sheet was made (example pictured at top), one could readily see whether the film density was consistent. In later years, commercial laboratories included back-printing on paper proofs which included film density. This made it easy for photographers to judge the quality of the decisions we made at the time of exposure (albeit after the fact).
Today, most of us rely on commercial scanning to produce positive film images. We often have no idea how much adjusting was done to create our scans. This can make it difficult to learn from our mistakes and create more satisfying film images. The image above (frame 10 of the above contact sheet) was scanned recently on my Pakon F135 Plus. Interestingly this is from a shoot in 1978. Upon examination, we can see that enough exposure was given to this soldier to develop shadow density and result in very satisfying black tones.
If you have your negatives scanned and would like to check your exposure, you can check the density of your negatives by holding them up to an even light source. The dense, dark areas of your negative, have received greater exposure, whereas the thin, almost transparent negatives have received less exposure. If across relatively similarly lit scenes you see an obvious variation in negative density, you might want to hone your metering technique to obtain more consistent exposure from one frame to the next.
My suggestion? Buy a proper incident light meter. You should find your exposures nice and consistent, which will lead to increased enjoyment for shooting film. Now go out there and shoot some film!