To understand exposure in photography it helps to have an understanding of film speed.
Film, film? Film. Ah yes! I remember hearing about film. That’s what they used to put in cameras in the old days!
Yep, it’s true. But many of the photography terms we used in the old days have been transferred to digital photography.
We don’t put film in cameras any more, but understanding film speed will help you to understand exposure, and that will help you to take better photos!
There are three things that can affect the exposure of a photograph. The shutter speed , the aperture and the film speed. Go back to my understanding exposure home page for more on shutter speed and aperture. For film speed . . . read on!
Enlighten me
To help you to understand exposure, even with a digital camera, you need to first go back to the days of film.
What happened was this . . . you put film into your camera, you started taking photographs. When it got a little darker (or maybe you went inside) you opened up the aperture and used a slower shutter speed. This helped let in more light from the scene.
But there was a problem. As it got darker still, and you had already opened the aperture up fully, and already lowered the shutter speed to as low as you dared go . . . then what?
Give up and go home? No way! Simply load a film into your camera that had a higher film speed.
So what was “film speed”? It's a measure of how sensitive film is to light. The “faster” the film, the more sensitive it was. The “slower” it was, the less sensitive it was.
The sensitivity was measured by the worldwide ISO standard. Fast film was considered to be anything that was ISO 800 or above. Slow film would be ISO 100 or below.
Film? Speed? ISO? Huh?
So what did all those numbers mean when it came to film speed? Well, the number related directly to how sensitive the film was to light. The most common type of film by far was ISO 100. That was the film almost everyone loaded into their compact cameras.
ISO 100 film was sensitive enough for taking photos in normal lighting conditions outside, and was OK inside with a flash.
ISO 200 was exactly twice as sensitive to light as ISO 100. ISO 400 was twice as sensitive again. And ISO 800 was twice as sensitive again . . . you get the picture!
Film speeds went up to ISO 6400 – incredibly fast film! Using this film would allow you to take photos indoors with no flash and just a few candles for light.
Why not always use a high film speed?
You might well wonder why people didn’t just buy the fastest film, and never have to worry about using a flash? Well, there were problems:
As the speed of film goes up, so does the amount of visible “grain”.
Faster films were far more expensive (to make and to buy).
Fast film could be too sensitive to light – you couldn’t get fast enough shutter speeds to avoid overexposure.
NB: ”Grain”
were the visible specks seen on photographs taken with fast films. They were often used to artistic effect.
What’s the digital equivalent of film speed then?
So, lots of talk about the speed of film in the old days of photography. But what of digital photography?
Naturally, we don’t put film into our cameras any more, so why is knowing about film speed relevant?
Well, we don’t use film speed, but we do have a digital equivalent. And we still use ISO numbers too.
Many cameras, even compact cameras, will have ISO settings. Some compact cameras, and all digital SLR cameras, will allow you to change them too.
So what effect does changing that ISO setting have? Well, clearly there’s no film in the camera; but what it does do is alter the sensitivity of the camera’s image sensor.
By adjusting the ISO upwards you make the image sensor more sensitive to light. This means you can still take photographs in low light without having to use shutter speeds so low that you end up with camera shake. And that would mean blurred photos!
You may well wonder why we don’t just use those high “film speeds” all the time in digital photography? Well, the same as using high film speed film in traditional cameras had its problems, so too does increasing the sensitivity, the ISO, in digital cameras. The problems are:
As the film speed (ISO) goes up, so does the amount of image noise.
If you set the ISO level too high, the image sensor becomes too sensitive to light and you end up with overexposure.
But there are benefits too (hurray!). If you find yourself taking photos in low light, and it would mean you end up with a slow shutter speed, you’d normally end up with a blurred photo.
But by increasing the camera’s ISO you can make the camera more sensitive to light, and you can use a faster shutter speed – no more camera shake and no more blurred low light photos!
And as for the consequences of image noise? Well, you may not notice this too much in the final print. And if you do, there is software that you can buy that will do a reasonable job of removing image noise.
Photoshop Elements is probably the best you can get as a home user.
Sidebar . . . One of the best things about digital photography is sharing the photos you take. However, because we end up taking so many of them, it’s easy to lose track of them all.
I recommend you give Google’s Picasa a try. It will not only organise your photos, but will perform minor edits too.
It’s all some photographers need, and best of all, it’s absolutely free!
Picasa comes as part of the Google Pack. If you don’t want the rest of the pack just de-select them when you get to the download screen.
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