ISO is one of three things you can change on your digital camera to get a better exposure. You can set the fstop (aperture), shutter speed and ISO to give you a good exposure. Each of these will affect how much light gets to the sensor.
The lower the ISO number, say 100, the less sensitive the sensor is to light. The higher the ISO number, say 1600, the more sensitive it is to the ambient light, meaning less ambient light is needed for a good exposure.
In the days of film, each roll of film had a “film speed.” Film speeds of 100, 200 and 400 were common. You could also find film with a speed of 1000 and 1600, but you usually had to go to a camera store to buy film this fast.
A roll of film with a speed of 100 is exactly the same as an ISO of 100 on a digital camera.
The big difference is that in the days of film you had to shoot up that whole roll before you could put in a new roll with a different speed.
Unlike film, you can change your “film speed” from frame to frame. ISO works by changing the sensitivity of the sensor to light.
I often shoot high school football games and will use ISO 1000 early in the game when the there is still a little daylight, and gradually increase the iso as it gets dark. I want to keep my fstop at f2.8 and shutter speed at 1/1200 or faster to stop the action. Since my lens is already wide open and I want to maintain the fast shutter speed, I can only increase the ISO to maintain a good exposure.
With my Canon 1DX Mark, my usual ISO for action sports at night 8000.
Just 10 years ago using an iso like 8000 would have been unheard of.
Understanding the negative side of using high ISO
Many years ago my brother though he found the perfect film when he began using 800 speed film to shoot everything.
“This film is great,” he told me. “You can shoot anything with it and it will turn out.”
Well, not so much. Using 800 speed film back then is like shooting at ISO 6400 on many of today’s digital cameras.
Photos taken with 800 speed film usually had a lot of grain, even if they were exposed correctly. That was just the down side of using fast film.
The downside of using a faster ISO, like ISO 1600, 3200, 6400 or 8000 is the digital “noise,” which is the same as grain in the days of film.
Sure, your camera may let you dial in an ISO of 51000, but would the pictures be usable? No all cameras and sensors are created equal.
It’s best to experiment with taking some photos with high ISO to see how far you can go before you start losing too much detail in the photo.
Let’s take a look at two Canon DSLR’s and how higher iso creates noise. We are comparing the noise of a 5D Mark III and a Canon 70D. A new 5D Mark IV costs more than $2500 and is a full frame (larger sensor) camera. The 70D is a APS-C sensor that costs about $800.
At 800 ISO, you can’t see that much difference between the 5D Mark III, left, and the 70D.
At an ISO of 3200, you can see the noise in the 70D image along the out of focus area on the left edge. The general sharpness of the image is also starting to suffer from the noise. All of the images in this test were shot using the same lens, the Canon 24-105 f4 L lens.
The noise at 6400 can really be seen in the 70D image. The digital noise is pronounced in that out of focus area on the left, while detail in wall of the lighthouse model has lost much of it’s sharpness. While you can see some noise in the 5D Mark III image, I would still consider it a very usable photo.
While it can be a little hard to see the difference when looking at the sample images above, the difference in image noise is obvious when peeking at pixels at 100 percent. The point is, while
Subject matter, lighting often
determine what ISO you should use
Sometimes you don’t have a choice but to use higher ISO. Shooting sports at night is a perfect example. You may also want to shoot a concert where flash isn’t allowed.
Most professional photographers will use iso 100 when shooting in studio so they can get the best detail in their images. Of course, using studio lights allows them to have the lighting they need to shoot inside with low iso.
Shooting outside in sunlight is also when you should lower your ISO to 100. It’s always best to use the lowest possible ISO. As a general rule, the lower the ISO, the less digital noise you will have in your images.
How to change your digital SLR camera ISO setting?
If you are shooting in manual mode, you can change the ISO by finding the ISO button on your camera and pressing it. Once pressed, the current ISO selection will be displayed on the top LCD panel. You can then use the selection wheel left of right to change the ISO. Or use the up down left and right buttons on the back of your camera to change the speed. If you don’t have an ISO button, refer to your camera’ss manual as it may be slightly different between brands and models.
P mode ISO priority
One of the modes on DSLRs is the P mode, or Program Mode. You can select this mode just by turning the dial on the camera to that mode.
When in the P mode, P the camera still sets the exposure for you but it unlocks other functions and is a good first step in moving from full auto mode to manual mode. In P mode, the camera picks the aperture and shutter speed, but it allows you to pick the ISO.
On many inexpensive DSLRs, one way the camera sets exposure in low light is increasing the ISO to such a high setting that the photos suffer from a lot of digital noise. By selecting the ISO, you can limit the digital noise. The camera then sets the fstop and shutter speed to give you a good exposure at the ISO you selected. You can also make a change to shutter speed or fstop and the camera will make an adjustment to the keep the correct exposure.
Sensor size and ISO
As a general rule, full frame sensors have less noise at high ISO settings than do crop sensor cameras.
Learn the limits of your camera and how much noise is acceptable to you.
Experiment with some photos, changing ISO as you take photos of the same subject. You may also need to put the camera on a tripod so camera shake won’t be an issue. Use the same fstop and ISO, and just use shutter speed to get the perfect exposure. Take the same photo (like the samples above) and use ISO 100, 200, 250, 320, 400, 640, 800, 1000, 1250, 1600, 2000, 2500, 3200, 4000, 5000, 6400 and 8000.
Download those photo and look for the digital noise in each photo. Most digital cameras handle digital noise fairly well up to ISO 800. What you want to look for is when the digital noise gets to be too pronounced for your taste.
Even the most expensive cameras have ISO settings that go beyond what you would use if you were shooting a photo to sell or give to someone. My Nikon D500 has ISO settings that go up to 51,200, but I wouldn’t set it higher than 20,000. Just because the setting is there doesn’t mean you should use it for everyday shooting.
