This is a question I’ve been asked a bit lately, so I thought a post on it might be appropriate. There is a lot of information out there about ISO and what it refers to, but I am going to give you my interpretation. Maybe not be absolutely correct, but it works for me.
ISO is a term that comes from film, those of you who remember film will remember that when you went to buy film you also had to decide what speed film you wanted. If you bought a 100 ISO film you were buying a slow film that was only good in good light and the grain of the film was very fine. If you bought a 400 ISO film then you would have used it in overcast conditions, and well lit indoors. If you bought a 3200 ISO film you would have been purchasing a film where the light conditions were very bad and you would have got very grainy images.
ISO in digital photography works on the same grounds.
This image was taken with a ISO of 100. I was using a tripod and time was not a factor, meaning it didn’t matter if the exposure was 1/250 of a second or 25 seconds. Therefore I could use a slow shutter speed and the best ISO to use was 100.
If I wasn’t using a tripod and I wanted to take photos of this, then I would have to use a shutter speed of, probably no slower than 1/60, that is the acceptable slowest shutter speed for hand held photography. With the shutter speed determining your exposure, assuming your aperture is around f16, then you will have to adjust your ISO to get the correct exposure. So you might have to put your ISO up to 400 or 800.
For most travel photography, you are outside and you can use 100 ISO, but what happens when the light gets bad and you don’t have your tripod and you want to capture other stuff? I photograph a lot of cycling, and I can’t use a tripod, so changing the ISO is really important. It is one of the changes I use the most, besides the shutter speed, but more on that another time.
I have to use my sports photos for the most of the examples.
This was taken at the Masters recently, the last day, it was raining and overcast. I can hand hold a camera down to around 1/15 of a second on occassion, but when you are photographing a moving target, you need a faster shutter speed. I had to up the ISO to 500 here to get the shutter speed that I needed to be able to capture the cyclists on their bikes as they rode past.
This image was taken using a tripod, but because it was so dark and I didn’t have a remote shutter release with me, I couldn’t use the Bulb setting, so I was limited to an shutter speed of 30 seconds, so to be able to get the correct exposure I put the ISO onto 400.
This image of World Champion Madison rider Cameron Meyer was taken at the Bendigo Madison earlier this year. The velodrome was outside and the Madison was at night, so light was limited. So like the previous image of the cyclists, shutter speed was important and capturing movement was also important. This was taken with a shutter speed of 1/30 of a second, and this was only possible by putting the ISO onto 1250.
When we go inside at stadiums there is little choice, you have to put the ISO up, especially with sport. The above image was taken at a Vixens Netball game last year. The light was bright, but to photograph something like netball, or basketball would be the same, you can’t use a flash, but you want to freeze the action in your images, so you need to have a fast shutter speed. This image was taken with a shutter speed of 1/320, which isn’t really fast, and this was using a ISO rating of 3200.
I hope this is all helping, here is another image.
This image was taken at the same arena as the netball, unbelievable that a velodrome is around the netball court. With this image I was using a flash, but still the shutter speed was important and to get the exposure I wanted I needed to use a ISO rating of 2000.
My advice would be to start with 100, once you have your aperture and shutter speed worked out, then look at your exposure. If it is too dark then you should put your ISO up. If you put it up too high then the image will be too bright.
Try going out this weekend, put your camera onto maual, put your shutter speed at 1/60 of a second and your aperture on f8 and keep changing the ISO until you get the right exposure. You can even let me know how you go.
If you want to read more on this, I found this website, just in case I confused you too much.
Have a great weekend with your camera.