The lower the ISO number, the slower the speed. The higher the ISO number, for example 1600 the faster the speed.
General Rules and tips for ISO Camera Settings:
- Use an ISO of 100 or 200 when taking photographs outside in sunny conditions.
- If the sky is overcast or it is evening time, then use an ISO within the range of 400 to 800.
- Night time or in cases of low light you might need to set your digital camera ISO to 1600. If you don’t then your photo will appear too dark if at all.
How does the ISO speed affect the photographs end result?
If you set your digital camera to a low ISO, for example 100, the resulting photograph will be better quality than one set at 1600. The higher the ISO the more grainy the photo will look. Therefore go for a low ISO number whenever possible.
However there are circumstances where a lower quality photograph is better than none at all. For example taking photographs of fish in a dark aquarium would normally be out of range for most point and shoot cameras. As you can see by the image below, setting my DSLR camera to a high 1600 ISO made this task possible. Otherwise there would not have been enough light let in to the sensor and the image would have turned out totally black.
Of course I could have chosen a lower ISO camera setting and used the inbuilt flash. However this would have resulted in unwanted flash glare bouncing off the glass. With this in mind a higher ISO (say 800) is also recommended if you want to take photographs of people inside in the evening without using a flash.