Commercial Photography Technique – ISO Sensitivity
Alongside aperture and shutter speed, ISO is the foundation of any serious commercial photographer’s exposure control system.
Only studio photographers enjoy the luxury of absolute control over the quality and quantity of the light falling on their subjects. Most other photographers, whether shooting indoors or out, must grapple with changeable and often woefully inadequate lighting conditions - an issue often faced with commercial photography and architectural photography. Inside a dimly lit theatre or concert venue, for example, you may find that even with your lens set to its largest aperture, a shutter speed that’s just a fraction too slow for shake-free handheld shooting is required.
You could always reach for your trusty tripod or inject a burst of flash, but this isn’t much use if you want to capture a moving subject or the use of flashguns and/or tripods is prohibited. You may also be deterred from using electronic flash because it has a nasty habit of destroying the natural ambience and colour balance of a scene. So what’s the answer?
Crank up your camera’s ISO sensitivity…
A global standard
ISO is the global standard for calculating and specifying the light sensitivity of photographic film. ISO is the short name for the International Organisation for Standardization, a worldwide confederation of national standards institutes from 146 countries. To avoid the confusion of different abbreviations in different languages, rather than using the acronym IOS, the organisation derived its short name directly from the Greek isos, meaning equal.
In the balance
To achieve any given exposure correctly, a photographer must balance three key elements: ISO sensitivity, aperture and shutter speed. The higher the ISO number, the more sensitive a film’s emulsion is to light. More sensitive films are referred to as ‘fast’ because they react to light quicker and require less time to expose properly. Less sensitive films react more slowly to light and are therefore referred to as ‘slow’.
Increasing the ISO from 100 to 200 doubles a film’s sensitivity to light, reducing the light needed for a well-exposed result by half. An increase from ISO 200 to ISO 400 doubles it again, cutting the amount of light required in half again. In practice this means that if, say, your required exposure at ISO 200 is 1/30th second at f2.8, switching your ISO to 400 at f2.8 would enable you to raise the shutter speed to 1/60th sec. By switching your ISO up to 800 at f2.8 you could increase your shutter speed to a more stable handheld shooting speed of 1/125th sec.
The main advantage of increasing ISO sensitivity, therefore, is that it enables you to select faster shutter speeds and smaller apertures when light levels are low. This not only gives you more control over depth of field, it also reduces the need to rely upon flashguns and tripods. All photographers will find this increased flexibility useful, but for sports, action, documentary, paparazzi, macro, travel, underwater, wildlife, nocturnal and creative commercial photographers, it’s invaluable.
But, as with all good things, this photographic feedom comes at a price. To reduce exposure times fast film emulsions need larger, coarser, less densely packed light-sensitive crystals than their slow contrast reproduction.
In photographic disciplines such as product, wedding, food, interior, wildlife, aerial, fashion, astronomy and architecture where detail and clarity is everything, fast films are a no-no. In B&W documentary, news, sports, entertainment, fine art, abstract and other creative photography, however, the distinctive characteristics of fast film can be perfectly acceptable, even highly desirable.
Upholding standards
Although electronic light sensors are used in digital cameras instead of film, they are sensitivity rated using the same ISO scale. Digital camera sensors are fundamentally slow devices though, with only one true ISO rating of either 100 or 200. Mastering ISO is a critical element within commercial photography and architectural photography. To circumvent this problem, digital cameras amplify the electronic signal output from their sensors, which has the effect of increasing their light sensitivity.
Entry level digital compacts are usually equipped with just one ISO 100 setting, while mid-range compacts generally feature at least two: 100, 200 and possible 400. More advanced ‘prosumer’ compacts may offer one or two additional fast speeds, such as 800 and 1600 and perhaps an extra slow ISO 50 setting. Digital SLRs often feature as many as 12 ISO settings, providing enormous flexibility. Indeed, with top ISO speeds reaching as high as 6,400, you may be able to shoot in near total darkness without a tripod or flash, provided you have a fast enough lens. One of the biggest advantages of shooting digitally is that you aren’t stuck with the same ISO setting for all your exposures. You can quickly and easily switch ISO sensitivity from shot to shot as prevailing lighting conditions and subject requirements change - an invaluable option for location commercial photography and architectural photography.
Quality trade-off
Unfortunately, one trait that digital cameras share with their film foils is that image quality drops as ISO sensitivity increases. Almost all electronic devices produce a continuous base level signal, even when they are on standby. In a digital camera this base level signal is generated by the sensor and manifests itself as background noise that varies erratically from pixel to pixel over time, worsening as the temperature rises. Provided the signal to noise ratio of the sensor is high (that is, good), there will be a clear separation between the useful light signal and the background noise, resulting in the capture of clean, precise, almost noise-free commercial photography and architectural photography. However, when sensor signals are amplified to boost ISO sensitivity, electronic noise interference is also increased. When this noise level rises to the extent that it begins to overlap the image signal level, noise becomes much more visible in images.
Primary colours
Another factor to consider is that digital camera sensors are typically less receptive to certain primary colours (particularly blue), so the signal output is often amplified in the weaker colour channels in order to compensate. This also adds to the base background noise and explains why noise levels are often greater in the blue and red channels than they are in the green channel. As with ISO, the culprit is electronic interference caused by signal amplification.
In digital images this noise interference is characterised by randomly spaced coloured pixels and a grainy, speckled texture that’s especially visible in shadow areas and in uniformly coloured areas such as skies. Faster ISO settings also tend to be beleaguered by oversaturated or washed out colours, colour shifts and poor contrast. The quantity and quality of this ‘grain’ at different ISO sensitivities is not dissimilar to that found in conventional film.
Nuisance noise
Many low-budget digital cameras exhibit high noise continuously, but in the majority of models visible noise starts to creep in at around ISO 200 or 320. The severity of this noise varies enormously from camera to camera and manufacturer to manufacturer. Consumer compacts are the worst hit, producing considerably more ISO noise than other types of model. This is partly because they use very small sensors that inherently suffer from more electronic interference. Mid-range and high-end compacts also use small image sensors, but tend to exhibit less image degradation because they’re equipped with more advanced noise reduction.
The anti-noise technology in compacts is improving with each new generation, but digital SLRs with their superior processors, components and noise removal algorithms still offer the widest and least noisy range of ISO settings. But no matter how advanced the noise-reduction, slow to medium ISO settings such as 50, 100 and 200 will generally offer smoother, subtler tonal transitions and sharper, more detailed images. Colour and contrast reproduction should also be more faithful. So unless your aim is to actually utilise noise effects for creative purposes, always endeavour to shoot at the slowest possible ISO, especially for finest quality work.
Your camera’s automatic ISO setting is also best avoided because it will automatically select fast ISO values in low light, regardless of the inevitable drop in quality. Furthermore, JPEG compression and interpolation algorithms greatly exacerbate ISO noise issues so, wherever possible, shoot in RAW mode. As with film, the penalty for superior image quality at slow speeds is decreased light sensitivity, which unless lighting is favourable leads to larger apertures and longer shutter speeds.
Ultimately, the key to success is to ascertain which settings on your camera give the most acceptable balance between image quality and speed. RAW converters such as Capture One have sophisticated noise reduction tools and anti noise utilities in Photoshop are worth experimenting with if shooting in JPEG as are plug-in noise busters such as Noise Ninja, Grain Surgery and Neat Image.
This article shows the quality and variety of techniques that customers benefit from as part of our commercial photography and architectural photography service. Call now to discuss your requirements and timescales on 079101 68536.
Copyright - Adam Coupe Commercial Photography 2008
