Hi Everyone! We've already talked about the first two parts of the exposure triangle:
aperture and
shutter speed. Today I'm going to discuss the last piece: ISO.
Has your brain turned to mush yet? :) If so, don't worry. ISO is easy probably the easiest of the three to understand.
First of all, I always wondered how to pronounce ISO. Do you say the individual letters like I-S-O? Or do you say Eye-Soh? (I don't really know, but according to some smart photographer people on You Tube, it's I-S-O.)
ISO refers to how sensitive your camera's sensor is to the amount of light present. It's measured in numbers like: 100, 200, 400, 800, 1600, 3200, 6400, 12,800, 25,600. The higher you set your ISO number, the more sensitive your sensor will be to light and the brighter your picture will be. Raising your ISO is very helpful in low light situations or situations where you need a faster shutter speed but don't have enough light to do so. Bump up the number and increase the brightness of your picture. Easy!
However...
Raising your ISO adds grain or digital noise (ugly dots/speckles) to your pictures. You always want to use the lowest ISO that you need to prevent adding unwanted noise. If you're outside on a sunny day, keep it at 100. I only raise my ISO
when I need to... on a very cloudy day, in the evening, or if I'm indoors.
It's important to note that some cameras handle noise at high ISOs better than others. My old Canon XSI handled it
horribly! I couldn't go beyond ISO 400 without the picture coming out very grainy and unusable. My new Nikon D7000 handles high ISOs incredibly. I don't worry about using high ISOs anymore and my new camera has enabled me to capture moments in low light that I never could have captured before. Take a look at
this shot in my Flickr stream that was taken at an ISO of 25,600!!
I often use a free program called
Noiseware to take out the digital noise that I sometimes get when I have to raise my ISO. I have the standalone community edition and it's great!
Here are some example pictures where you can see what I mean about grain:
The photo below was taken with my 50mm at f/1.8, 1/100, ISO 100 (the lowest ISO setting).
It's difficult to see at this size, so let's zoom in to a 100% crop to see how clean the image looks.
The photo below was taken a second later at f/1.8, 1/800,
ISO 3200 (a high ISO setting that added digital noise).
Again, it's difficult to see the grain until we zoom in. Can you see all of the spots and speckles now?
So to wrap things up, if you're in low light and you have to raise your ISO as a last resort, do it. It's better to expose your photo properly with a higher ISO than to underexpose your image. Increasing the brightness of an underexposed image in Photoshop will add noise anyway, so always go for the correct exposure in camera. However, if you can do other things to let in more light like widening up your aperture (lower number) or decreasing your shutter speed (without it getting too low to add motion blur), do that first.
My next post in the
Learning Together series will be about putting it all together in the real world: aperture, shutter speed, and ISO.