In a series of Intel on photography, I have offered a lot of ideas on problems and tips to improve photography. In this Intel I want to move away from the how to of making a better photograph and look at a more “advanced” aspect of image making, the critical aspect of understand light and how it interacts with the subjects you see through your viewfinder. Photography involves an awareness of how a subject is changed under different lighting conditions
Daylight - The low, broad illumination of early morning and evening, the strongly directional light through the daylight hours, and the soft, diffuse light of an overcast day.
Direct sunlight is directional. It creates strong shadows and bright highlights, quite the opposite a cloudy sky, which seems to come from everywhere, casts soft or no shadows, and creates subtle or no highlights.
Indoors - Standard light bulbs heat a tungsten filament which produces a light which appears quite similar to daylight to the human eye but which is in fact, very much redder than daylight. Fluorescent tubes compact “environmental” bulbs utilise a phosphor coating on te inside of the glass to convert ultraviolet light to white light - except, again, it isn’t really white. The actual colour depends on which phosphors are incorporated into the coating. Our brains easily compensate for the variations in colour: If it did not, we would see objects as different colours under different light sources. If the colour shift is sufficient, of course, that is what happens. “Black light” makes a great party light, but only because it is so different from “normal” that our eyes don’t drag hues back to their “correct” shades.
Camera sensors and film are less subjective. They always react the same way. Film is very sensitive to the quality of the light and can react very differently when the light falling on the subject changes. Digital sensors have the advantage of a computer to measure the colour of the light (its “colour temperature") and compensate, and it usually does a good job - but not always. A photographer must learn to recognise the character of the light used to illuminate the subject.
Correcting Light Imbalances - The film photographer has several options to deal with variations in the colour of light. They may choose a film that is balanced for the type of light ... for instance, a "tungsten-balanced" film that can be used in tungsten light and still produces an image with colours that look more or less the same as when shot with outdoor daylight. However, there are limits to the variety of films one can buy. Instead, you can opt to use daylight film and add filters to your lens to compensate for the light. Again this has limitations in that filters require increased exposure, and again, not all light can be corrected. The third option is to convert the final image into a digital file, and correct the colour in the computer. This is the same approach that digital photographers must use.
The digital photographer must also make some choices.
1. In camera compensation: the computer in the camera can be left to estimate the colour of the light and compensate (AWB or ‘automatic white balance’); the AWB can be over-ridden and you can set the WB manually from a menu of choices, or you can set a custom white balance. This involves showing the camera a white or grey surface which becomes the reference for the light in the scene.
2. Post-processing: software “fixes” allow either manually removing colour castes or nominating a “true” white, black and/or grey in the image, which the computer can then use as a reference for the whole picture. This is a useful procedure for most images, but is far more powerful when applied to RAW images, from which has not already applied colour modifications that must be discarded, and from which no information has been dropped as it has been in jpeg and tiff conversions.
Colour Temperature - Daylight is not a fixed colour either. It varies from season to season and from country to country. The theoretical average daylight used to calibrate film/sensors, assumes that daylight is composed of yellowish sunlight plus blue light from a partly clouded sky, from two hours after sunrise until two hours before sunset, in latitudes when the sun is nearly perpendicular to the ground. This colour is ascribed a “Colour Temperature” of 5500 degrees Kelvin. How often does that apply where you take photographs?
Colour temperature - As any body grows hotter, it radiates heat. When it gets hot enough, that radiance becomes visible as light. Colour Temperature describes the changing colour of the light emitted by a perfectly black object as it is heated. At temperatures between 15000 K and 18000º K our theoretical black body will emit coloured light ranging from red to blue, the colour of deep-blue sky during the day. The temperature is measured in degrees Kelvin, starting from absolute zero (-273.15º Celsius).
Since our “average” daylight is nominally 5500º K all daylight films are balanced for this colour. Artificial light films (type B) are balanced for 3200º K which is the colour of light emitted from tungsten-halogen lamps used in studio lighting.
Evening or morning daylight has a colour temperature of 5000º K and household lamps vary from 2650 to 3000º K for 40 to 200 watt bulbs. Electronic flash has a colour temperature of 5500 to 6000º K.
Mired values (MV) are the reciprocal of the colour temperature multiplied by one million, or MV = 1,000,000 / ºK. Decamired values are mireds divided by 10. Mired Values are assigned to lights (MVl); and to filters as mired-shift value (MVf). MV for light are always positive while those for filters can be positive (for warm coloured filters ‘orange or amber’) or negative (for cold coloured filters ‘blue’).
Light Sources -
Modern studio lights have quartz envelopes rather than glass and are filled with an inert halogen gas like iodine, similar to car headlights. They have a colour temperature of 3200º K.
The older studio lamps (photofloods or just “floods”) had glass envelops and built-in reflectors. To get a “white” output id t was necessary to run them at a high voltage, which meant they lasted only a few hours and were uncomfortably hot to work under. They had a colour temperature of 3400º K. Suitable films for them are called artificial-light films (type A).
White light-emitting diodes (LED) emitting white light are a promising development in lighting as they consume about one tenth of the power of filament lamps, (their “lumen per watt ratio” is very high). It is possible to specify their CT but off the shelf, some are ‘cold light’ at 8000º K, while others have a CT of 4500º K.
Gas-discharge lamps are usually xenon-filled, and used in electronic flashes. Like neon tubes, they are of the pulsed nature, so are not rated for CT; some do provide continuous light and can be used with filters to give acceptable results. Other sources, like metal-halide lamps are being developed for photographic use, and have already started to appear in data projectors. They have a colour temperature of 6000º K and also have very high efficacy (lumens per watt) which is more than halogen lamps. Other sources that can be corrected using filters are Mercury Vapour and High-Pressure Sodium Vapour lamps. It is not possible to correct Low-Pressure Sodium Vapour lamps.
Subjective Colour Sensitivity and Reality - Now we’ve established the basics of accurate, scientific colour evaluation and True Colour, a dose of reality.
Every film and every sensor renders the same scene slightly differently. It is one thing to have an objective way to measure the colour of the light that leaves the subject but that has only a little bearing on what we consider a true or accurate representation. "Truth" in photography is a matter of debate.
There is no film that renders "reality," and if there is more consistency between electronic data arrays than between films, I haven’t noticed it yet! The rendition you choose is central to your creative control and one of your responsibilities as a photographer. Whether this directs your choice of film, your camera setup, or the scripts and workflow in your digital darkroom, it is a significant of the subtle quality we recognise as your photographic style.
What's pleasing to you about how a particular film or camera set-up renders a subject/light situation may not be pleasing to someone else. There are many different choices and some of them have very specialised uses (for shooting in daylight film in tungsten light, for capturing infrared images, etc.).
Editing programs (PaintShopPro, GIMP, PhotoShop etc.) let you manipulate the image to look more or less like what it would have been had the photo been as you remember it or intended it to be. The photographer's choice determines which image is most pleasing to the photographer.
Photographers who understand light gain the ability to anticipate how the camera is going to interpret the subject. They know how the shot is going to turn out. This is an exceedingly powerful capability, available only through experience. Reading this intel, or guide books or going to lectures will not get you there!
Photographers are often disappointed with their images because what they saw with their eye was not captured by the camera. In many cases, it might not have been possible for an experienced professional to capture what someone can see with their eyes. Sometimes experience leads to not shooting an apparently exciting subject, because the light and equipment at hand simply can't achieve the desired result.
With a clear understanding of your medium, [i[light, you will be able to make great photographs in situations where most snapshot photographers wouldn't even try. Rather than trying to record what your eyes (and brain) are seeing you will be able to visualise the response of the medium to the situation to produce consistently superior results.
