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Film Speed and ISO Numbers |
As usual, in order to make this feature work, we need some standard way of specifying film speed ratings and of relating them to the other settings available on our camera.
Shutter speed and aperture settings a related to each other via the f-stop so it seems sensible to use this to link in film speed.
Remember that changing the shutter speed halves the amount of light passing through it for each increase in speed and doubles the amount for each reduction in speed, hence a shutter speed of 1/125th allows twice the amount of light through than 1/250th.
Similarly, opening or closing the aperture one stop at a time doubles or halves the amount of light to reach the film.
The sensitivity if the film is arranged in exactly the same way, in that each increase in sensitivity requires one stop less light in order to form an image.
The manufacturers use the ISO (International Standards Organisation) number to indicate film speed so you will come across numbers like ISO100, ISO400 etc. Just like shutter speed settings, each doubling of the number is equivalent to one stop, so the ISO400 film will two stops faster than the ISO100 film. If you change from 100 to 400, you will need to either close your aperture by two f-stops, increase you shutter speed by two stops or change each by one stop.
But I'm Using a Digital Camera
Yes, you are not using film, so why should you be bothered about film speed?
Well, there must be a reason why we have the ability change ISO numbers on our digital cameras because cost-conscious manufacturers don't like giving us expensive extra features if they can help it.
We need to look at the advantages offered by this feature to understand why we've got it because if it was not genuinely useful, it would not be there.
O.K., So What Use Is It?
Broadly speaking, there are three sets of circumstances that will have you considering ISO numbers.
- Low light conditions
- Fast action shots
- Studio or indoor portrait work
Low Light
This can refer to indoor work where you cannot control the light source or perhaps don't want to use flash, or working near dawn or dusk when there simply isn't much light about.
In these conditions, using a fast film, perhaps ISO400, 800 or even 1000 or more, may be necessary to prevent you being limited to large apertures, slow shutter speeds and maybe even a tripod to get the shot.
Action Shots
In order to freeze the action at a sports event, you need to use fast shutter speeds. On a dull day or at an indoor event this can give you problems in that you will need to compensate with a large aperture setting. This can bring it's own problems relating to depth of field, especially as you are likely to be using a long telephoto lens which may not even have a large enough aperture setting.
This is where high ISO numbers of 800 or above can give a real advantage because you may not be able to work at all without there aid.
Portrait Work
This kind of work requires a change of film speed for a different reason.
Portrait work normally requires a very high standard of work with a great degree of accuracy relating to colour, tone and detail. You also usually have much more control over lighting so have plenty of flexibility in other areas.
Slow film with low ISO numbers, from 64 and below, produce very highly detailed images almost totally free from grain, which is exactly what you want for portrait work.
Because they require a lot of light, you also have a lot of freedom to be creative with your lighting equipment.
So It Is Usefull Then!
You can see from the above that the ability change film speed on a digital camera is in fact a very usefull feature, but there is one thing you need to consider that we have not mentioned yet.
Shooting at high speeds onto high speed film produces a grainy image. This can give an image a gritty, atmospheric ambience that can enhance some images, but may not always be appropriate. For this reason, don't simply set your camera at it's highest ISO number. Grab your camera and experiment first so that you are aware of what the final image will look like.
Get used to considering film speed and it will open up new avenues for your work. Not only will you find yourself taking images in circumstances that would have been impossible before, but it will also open up new areas of creativity if you remember the graininess and contrast available at higher ISO numbers and the level of detail available at low numbers.
Why not grab a no-charge copy of my Manx Norton screen saver yourself so that you can see exactly what we're talking about?
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- the name of the free/lo-cost software I used and where to get it
- an occasional e-mail with details of other money-spinning digital photo ideas
along with details about how I am getting on with them
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Now, I said earlier that there were lots of ways to make some money from your
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If you filled in the little form above and got hold of the goodies I promised, I'll also send an occasional e-mail with other great ideas for you to try. In the mean time, if you want a dozen more excellent ideas right now, take a look at this:-
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