by Gerald Boerner
This examination of “Drawing with Light” completes our examination of the settings and cameras that enable us to create images of the external world. The originators of the photographic process, Louis Daguerre and William Henry Fox Talbot, both saw photography as a way of using light to expose photosensitive materials (film or digital sensor). This process has been refined since that time and now allows us to capture images in even near dark through the use of high ISO in some of the latest professional cameras. Enjoy and try some of these techniques in your own photography. GLB
“A novel is never anything, but a philosophy put into images.”
— John Rohn
“A lot of the images in my work are a kind of visual diary of places I’ve been, what I’ve seen, heard, smelt.”
— Francesca da Rimini
“A number of images put together a certain way become something quite above and beyond what any of them are individually.”
— Francis Ford Coppola
“An artist cannot be responsible for what people make of their art. An audience loathe giving up preconceived images of an artist.”
— Stephen Stills
“And I also see how this body influences external images: it gives back movement to them.”
— Henri Bergson
“All of a sudden, those few pages of script that he had shown me with the weird images I could visualize all of that in my brain, and I knew that there was this mad little genius at work here and I really wanted to do the film.”
— Jack Nance
“A man’s work is nothing but this slow trek to rediscover, through the detours of art, those two or three great and simple images in whose presence his heart first opened.”
— Albert Camus
“Although images of perfection in people’s personal lives can cause unhappiness, images of perfect societies – utopian images – can cause monstrous evil. In fact, forcefully changing society to conform to societal images was the greatest cause of evil in the twentieth century.”
— Dennis Prager
Drawing with Light: Film Speed and ISO Settings
Film speed is the measure of a photographic film’s sensitivity to light, determined by sensitometry and measured on various numerical scales, the most recent being the ISO system. Relatively insensitive film, with a correspondingly lower speed index requires more exposure to light to produce the same image density as a more sensitive film, and is thus commonly termed a slow film. Highly sensitive films are correspondingly termed fast films. A closely related ISO system is used to measure the sensitivity of digital imaging systems. In both digital and film photography, the reduction of exposure corresponding to use of higher sensitivities generally leads to reduced image quality (via coarser film grain or higher image noise of other types). Basically, the higher the film speed, the worse the photo quality.
Film speed systems
The current International Standard for measuring the speed of color negative film is called ISO 5800:1987 from the International Organization for Standardization (ISO). Related standards ISO 6:1993 and ISO 2240:2003 define scales for speeds of black-and-white negative film and color reversal film. This system defines both an arithmetic and a logarithmic scale, combining the previously separate ASA and DIN systems.
In the ISO arithmetic scale, corresponding to the ASA system, a doubling of the sensitivity of a film requires a doubling of the numerical film speed value. In the ISO logarithmic scale, which corresponds to the DIN scale, adding 3° to the numerical value that designates the film speed constitutes a doubling of that value. For example, a film rated ISO 200/24° is twice as sensitive as a film rated ISO 100/21°.
Commonly, the logarithmic speed is omitted, and only the arithmetic speed is given; for example, “ISO 100”.
Upon exposure, the amount of light energy that reaches the film determines the effect upon the emulsion. If the brightness of the light is multiplied by a factor and the exposure of the film decreased by the same factor by varying the camera’s shutter speed and aperture, so that the energy received is the same, the film will be developed to the same density. This rule is called reciprocity. The systems for determining the sensitivity for an emulsion are possible because reciprocity holds. In practice, reciprocity works reasonably well for normal photographic films for the range of exposures between 1/1000 second to 1/2 second. However, this relationship breaks down outside these limits, a phenomenon known as reciprocity failure.
Film sensitivity and Grain
Film speed is roughly related to granularity, the size of the grains of silver halide in the emulsion, since larger grains give film a greater sensitivity to light. Fine-grain stock, such as portrait film or those used for the intermediate stages of copying original camera negatives, is "slow", meaning that the amount of light used to expose it must be high or the shutter must be open longer. Fast films, used for shooting in poor light or for shooting fast motion, produce a grainier image. Each grain of silver halide develops in an all-or-nothing way into dark silver or nothing. Thus, each grain is a threshold detector; in aggregate, their effect can be thought of as a noisy nonlinear analog light detector.
Kodak has defined a "Print Grain Index" (PGI) to characterize film grain (color negative films only), based on perceptual just noticeable difference of graininess in prints. They also define "granularity", a measurement of grain using an RMS measurement of density fluctuations in uniformly-exposed film, measured with a microdensitometer with 48 micrometre aperture. Granularity varies with exposure — underexposed film looks grainier than overexposed film.
Digital Camera ISO Speed and Exposure Index
In digital camera systems, an arbitrary relationship between exposure and sensor data values can be achieved by setting the signal gain of the sensor. The relationship between the sensor data values and the lightness of the finished image is also arbitrary, depending on the parameters chosen for the interpretation of the sensor data into an image color space such as sRGB.
For digital photo cameras ("digital still cameras"), an exposure index (EI) rating—commonly called ISO setting—is specified by the manufacturer such that the sRGB image files produced by the camera will have a lightness similar to what would be obtained with film of the same EI rating at the same exposure. The usual design is that the camera’s parameters for interpreting the sensor data values into sRGB values are fixed, and a number of different EI choices are accommodated by varying the sensor’s signal gain in the analog realm, prior to conversion to digital. Some camera designs provide at least some EI choices by adjusting the sensor’s signal gain in the digital realm. A few camera designs also provide EI adjustment through a choice of lightness parameters for the interpretation of sensor data values into sRGB; this variation allows different tradeoffs between the range of highlights that can be captured and the amount of noise introduced into the shadow areas of the photo.
Digital Cameras technology has far surpassed film cameras in terms of sensitivity to light and controlling image noise and film grain. Digital cameras have up achieved ISO’s up to 102,400, a number film speeds never got close to.
How to Understand & Use ISO Speed for Photography
The eHow.com article referenced below should help you understand how ISO settings will help you get better photos. We have sachphotography to thank for the following suggestions. Please take a look at the original article and this contributor’s site for more information.
In this article, I would like to help the reader to grasp a better understanding of how to use different film speeds on their digital camera. While my article focuses on DSLR cameras, the basic principles may be used when shooting film.
ISO….ASA…. What does it all mean? What is the difference between 100 and 1000?
The ASA (American Standards Association) scale is an arbitrary rating of film speed. This is not typically used anymore as the mass has merged into a worldwide use of the ISO standard. Derived from the Greek "isos", meaning "equal", The International Organization for Standardization chose this short all-purpose name instead of using its acronym "IOS" so that whatever the country and language, the short form of the organization’s name is always "ISO" (pronounced "eye-so" but typically pronounced as "EYE-S-OH").
To put it simply, the higher the ISO number the faster the speed of the sensor or film. Film speed describes how fast, or sensitive, the sensor or film absorbs the light that falls upon it. I will mainly focus on the digital side as the majority of today’s photographers lean more heavily towards digital.
Most Semi-Pro and Pro digital cameras allow you to adjust the iso sensitivity.
The majority of low to mid-range digital cameras have an ISO range that goes from somewhere in the neighborhood of 50 or 100 up to around 400 to 800. A lower ISO number requires more light to obtain a proper exposure on a given shot.
The majority of people would be inclined to turn the ISO setting all the way up to obtain the most light possible. What is wrong with this? Although a higher ISO setting will absorb more light and capture a good exposure even in low light, there is a problem. The higher you set the ISO, the more "noise" there will be, causing your pictures to come out grainy.
With Technology today there are ways to employ higher ISO setting without developing a fuzzy photo.
These days, many digital cameras utilize some form of noise reduction for their higher ISO settings.
Though at first glance reducing noise may seem like a good route to go, it also has its own downfall. Reducing noise is often accomplished by utilizing small amount of blur. Though you may be able to blur out the noise, you will blur out the fine detail you are trying to capture.
In general, you would typically want to use the lowest ISO setting as possible. The key benefit to using a digital camera is the ability to find the perfect setting instantly. A photographer is able to shoot a photo and see it instantaneously giving him the ability to make corrections and shoot again
For a clean photo a photographer would want to use a lower ISO setting.
When using a lower ISO setting, light is not always readily available. There are two distinct way to compensate for lighting issues when using a low ISO. A photographer will change the shutter speed to allow the shutter to stay open for a longer period of time, allowing more light to pour onto the sensor. If a photographer uses a longer shutter speed, generally the camera will be mounted on a tripod, a mono pod, or some other form of bracing.
One additional option to obtain proper lighting, is to utilize a flash.
A key to using a flash is to not bath the subject being photographed in direct light unless desired. Play around with different flash settings to obtain the desired results.
When shooting with a digital camera, a good starting ground is to set you ISO to 400 and adjust from there. Lower ISO equals less grain and more clarity.
More Suggestions for Using ISO
The article on Digital Photography School on ISO cited below makes these further suggestions. Please look at the full article for more information.
100 ISO is generally accepted as ‘normal’ and will give you lovely crisp shots (little noise/grain).
Most people tend to keep their digital cameras in ‘Auto Mode’ where the camera selects the appropriate ISO setting depending upon the conditions you’re shooting in (it will try to keep it as low as possible) but most cameras also give you the opportunity to select your own ISO also.
When you do override your camera and choose a specific ISO you’ll notice that it impacts the aperture and shutter speed needed for a well exposed shot. For example – if you bumped your ISO up from 100 to 400 you’ll notice that you can shoot at higher shutter speeds and/or smaller apertures.
When choosing the ISO setting I generally ask myself the following four questions:
- Light – Is the subject well lit?
- Grain – Do I want a grainy shot or one without noise?
- Tripod – Am I use a tripod?
- Moving Subject – Is my subject moving or stationary?
If there is plenty of light, I want little grain, I’m using a tripod and my subject is stationary I will generally use a pretty low ISO rating.
However if it’s dark, I purposely want grain, I don’t have a tripod and/or my subject is moving I might consider increasing the ISO as it will enable me to shoot with a faster shutter speed and still expose the shot well.
Of course the trade off of this increase in ISO will be noisier shots.
Situations where you might need to push ISO to higher settings include:
- Indoor Sports Events – where your subject is moving fast yet you may have limited light available.
- Concerts – also low in light and often ‘no-flash’ zones
- Art Galleries, Churches etc- many galleries have rules against using a flash and of course being indoors are not well lit.
- Birthday Parties – blowing out the candles in a dark room can give you a nice moody shot which would be ruined by a bright flash. Increasing the ISO can help capture the scene.
ISO is an important aspect of digital photography to have an understanding of if you want to gain more control of your digital camera. Experiment with different settings and how they impact your images today.
Bryan Peterson. (1996) Exposure. AMPhoto
Background and biographical information is from Wikipedia articles on:
Wikipedia: Film Speed…
Other Web Sites:
eHow.com: How to Understand & Use ISO Speed for Photography…
Digital Photography School: ISO Settings in Digital Photography…