ISO film speed is determined by the International Organization for Standard-ization (the ISO), a network of national standards
institutes from 161 countries. It is based in Geneva in Switzerland but is non-governmental in its organisation.
The function of the ISO is to set standards in commerce and industry. One of these standards is the ISO film speed rating for the sensitivity of
photographic (emulsion based) film
According to the ISO, 800 speed film is more sensitive than 400 speed film, and 400 speed film is more sensitive than 200 speed film
and so on. The more sensitive the film, the faster it is said to be and the less light you need in order to take a picture.
Without getting too technical, the speed of
the film is calculated from the optical density (the absorbance of light by a material such as film) and the exposure time using a mathematical equation.
But more importantly is how to choose the right ISO film speed when you are shooting so read on below.
Using Film Speed Effectively
The size of the grains of silver halide in film emulsion determine the film speed. Bigger grains means greater light
sensitivity and vice versa. An ISO film speed of 50 (that is, a slow film speed) is great for potraiture as the grains of
silver halide are smaller and therefore the result will be literally more fine grained. Fast film speeds of 800 or more
have bigger grains and are good for shooting when the light is poor or if you want to freeze something in fast motion.
However, the result will look coarse grained. Also bear in mind, that if you underexpose your shot the result will be even
more grainy than if you overexpose it.
In normal day-to-day use, a film speed 100 or 200 is adequate, usually when shooting out of doors when there is a fair amount of sunlight
available or at least bright sky with some cloud. 400 and 800 speed film are more suitable for indoors particularly when you
don't want to use flash.
Film versus Digital
Of course the main problem with using film is that if you want to alter the ISO rating you actually have to change the film itself
or have an interchangeable back. With a digital SLR you can change the ISO settings frequently, sometimes for
each individual shot. Digital cameras have ISO settings which go beyond 800, up to 1600 or 3200 or even more which means you don't need
to fire the flash. At 1600 ISO you can probably take a shot hand-held at about 1/30 second indoors in poor light.
Film Grain Agfa 1000 RS Slide
Another drawback with film is that with higher ISO settings you get more 'grain' (called 'noise' if you are using a digital
camera). In the above photo you can see an example of 'grain' on a slide film that has an ISO setting of 1000. Nowadays this
is considered undesirable and indeed if you are photographing a sunset or a flower in close-up that is probably true. But
some people still value grainy images as they have a more photojournalistic or documentary feel and grain can create an interesting mood in
If you want the least possible grain or noise in your images go for the lowest possible ISO setting such as
100 or even 50. Just make sure you have a tripod as the shutter speed will need to be correspondingly slower.
Kodak film ISO goes down as low as 6. So far as I know there isn't anything lower than that!
If you are about to buy a new camera and want one with the lowest possible amount of digital noise, go for a Canon as they
are renowned for their lack of noise, particularly the EOS range. I have used Canon EOS cameras for many years now and
because the level of digital noise is so low, I have become used to shooting without flash most of the time. If you really want
to buy a superb camera go for the Canon EOS 5D Mark II as digital noise is absolutely minimal.
After the Event
If you do have a great shot that you took with an ISO setting of 800 or more and it has too much 'grain' you can manipulate
it in Photoshop once it is scanned. I use Noise Ninja which is a plug-in for Photoshop. After you have downloaded the
programme you can get a profile for your camera from the Noise Ninja website. Install that after you've installed Noise Ninja and then whenever you open
an image in Photoshop, Noise Ninja will detect automatically the ISO film speed or setting that you used and will apply their
custom-made filter. It is easy to use, inexpensive to buy and the quality of the results will astonish you.
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