Explain ISO

[Sleepy]

So I've started learning my DSLR a little better, but still not real happy with my knowledge. I know the camera is way better than I am. I've learned somewhat on my ISO settings, but was wanting to hear it from you guys. And before you tell me to google ISO, I know I can do that, I just want to hear it from someone that I can ask questions and get a better understanding. I know ISO situations vary on light conditions, and I know the lower ISO in more light and higher ISO in less light. But how do you really know what ISO to use? Do you just have to mess around with it or is there a golden rule? Id like some good info on it.

Thanks in advance!

[PSD Ryan]

When I'm planning a photo, I usually pick my F stop first. If it's a moving subject, I pick my shutter speed, then adjust the ISO to the lowest setting that gives me enough light. If I am taking a picture of a still item, I use a tripod, keep the ISO at the lowest setting, then adjust the shutter speed for the correct light since timing is not as important.

I think of it as F-stop + Shutter Speed + ISO = desired light. If you lower one, you have to compensate by increasing another.

Basically, low ISO...cleaner image. High ISO, noisier/grainier image.

[Bonesplitter]

[Limbwalker]

Love that graphic!

ISO back in the film days equaled grain. Tighter grain looked better, but required more light to properly expose it. Faster film had big grain, which exposed quickly, but showed up in the image. That's why we all tried to shoot the lowest ISO film we thought we could get away with.

These days, the best digital cameras offer virtually imperceptable differences between ISO 100 and 400. Some even have ISO 800 that looks fantastic.

This is almost inconceivable to an old film shooter like myself. I would never, ever have used 400 speed film for any serious subjects in my film days. I once used 1600 ISO film to photograph an indoor theatre performance in Rockport for their Chamber of Commerce, but that was the only reason I'd ever go that fast.

Today, with my 7D, I often shoot up to 3200 with my 600mm lens, because the noise is still acceptable, and it keeps the camera shake to a minimum.

400 ISO is my stock setting now for wildlife photos with my long lens. If I'm shooting landscapes on a tripod, I still try to shoot them at 100 ISO, and if I'm trying to blur water, I wish I had an ever slower option.

John

[Reaper33]

in photography I have found there isn't really any golden rule at all just shoot, shoot, shoot and change everything around. That's what I like about pictures, you can take the same one 10 different ways and get 10 different results. Im not a believer in if you take it right its perfect bc 9 out of 10 times the picture I thought I would like the best or thought I took the best isn't the one I like the most.

[Shane]

Lower ISO means your sensor is LESS sensitive to light, so your pictures will be darker compared to the same pic with higher ISO (when all other settings remain the same).

Higher ISO means your sensor is MORE sensitive to light, so your pictures will be brighter compared to the same pic with lower ISO.

The analogy that I use for the 3 main settings (ISO, shutter speed, and aperture) is this....

The aperture, designated by f/stop number, is similar to the pupil in your eye. The bigger the aperture/pupil, the more light comes in. The only thing that can be confusing is that lower f/stop numbers equate to bigger aperture openings. So f/22 is a really small opening that lets in only a tiny amount of light while f/2.8 is a really large aperture that lets in a lot of light. If you are shooting a scene in bright sunlight, then you can choose a small aperture setting (bigger f/stop number), because you have a lot of bright light to work with. If you are shooting a scene in dim light conditions, then you will probably need to set the f/stop to a low number so you'll have a big wide-open aperture to let in as much light as possible.

The other thing that aperture size will do for you, besides regulating the amount of light passing through the lens, is that it will vary the depth of field. Depth of field is the depth of what is in focus in your image. A tiny aperture opening will bring more things into focus. Things that are both near and far away, relative to whatever you focused the lens on when you take your shot can generally be more in focus with a smaller aperture. If you want to have a narrow depth of field so that only your subject is in focus while everything else is blurred out, then you need to use a larger aperture (low f/stop number).

Next we get to the 2nd setting: shutter speed. The shutter is similar to your eyelid. The longer it stays open, the more light it lets in. If it opens and shuts really fast, then only a small amount of light gets in. If you are in bright light, then you'll likely need to use a faster shutter speed. If you are in low light, then you'll probably need to use a slower shutter speed.

Shutter speed variations do something else as well. If you want to freeze fast-moving objects, like stopping the action in sports photography, then you need a fast shutter speed. But if you want to show the blurred action of moving objects, then you need the shutter to be open for a longer time in order to pick up all the movement that you are after.

The 3rd setting is ISO. A high ISO number (1600, 3200, 6400, etc...) is like your naked eye. It is very sensitive to light, and it picks up detail very easily. You may need to squint or open and shut your eyes really quickly when it is really bright.

A low ISO number is like your eye behind sunglasses. It makes your eye less sensitive to light, so you don't have to squint and you can leave your eyes open longer in bright light. But in dim light you may not be able to see very well, so you'd need to remove your sunglasses.

ISO also has another effect on the photo. Higher ISO numbers will make photos in low light situations brighter, but it comes with a price. Higher ISO settings cause the image to have more "noise" or grainy appearance.

Everything about choosing camera settings is a trade-off. You have 3 different settings that you could adjust to make an exposure brighter or darker, and each of the 3 have side-effects. Which side-effect do you want? Which one do you NOT want? Which one can you live with if you have to, even though you'd prefer not to have it?

I start with the side-effect that I want, and then I work from there. If I am shooting sports, then I definitely want to stop fast action. That means I must have a fast shutter speed. That costs me light, so if I am not shooting in bright sunlight then I have to open up my aperture and/or move to a higher ISO setting. I go to higher ISO as a last resort, because I want to minimize noise. But once you open up your aperture all the way, if you still need more light in order to get a good exposure with a fast shutter, then you have to start boosting ISO.

If I am shooting a portrait or something and I want only my subject to be in focus while everything in the background is blurred out, then I must shoot the shot with a large aperture (low f/stop). That lets in a lot of light, so if I have fairly bright light to begin with, then I will need to shoot a low ISO and/or a faster shutter speed to keep from over-exposing the shot.

There are always more than one combination of settings that will give you a proper exposure of light in a given situation. But the side-effects will vary, depending on which combination of settings you use. It's all about the trade-offs.....

[Terrychester]

Explained 1000 times better than what was explained when I took a photography class 30 years ago.

[ClayW]

Saving for later

Great explanation guys

[Sleepy]

Lower ISO means your sensor is LESS sensitive to light, so your pictures will be darker compared to the same pic with higher ISO (when all other settings remain the same).

Higher ISO means your sensor is MORE sensitive to light, so your pictures will be brighter compared to the same pic with lower ISO.

The analogy that I use for the 3 main settings (ISO, shutter speed, and aperture) is this....

The aperture, designated by f/stop number, is similar to the pupil in your eye. The bigger the aperture/pupil, the more light comes in. The only thing that can be confusing is that lower f/stop numbers equate to bigger aperture openings. So f/22 is a really small opening that lets in only a tiny amount of light while f/2.8 is a really large aperture that lets in a lot of light. If you are shooting a scene in bright sunlight, then you can choose a small aperture setting (bigger f/stop number), because you have a lot of bright light to work with. If you are shooting a scene in dim light conditions, then you will probably need to set the f/stop to a low number so you'll have a big wide-open aperture to let in as much light as possible.

The other thing that aperture size will do for you, besides regulating the amount of light passing through the lens, is that it will vary the depth of field. Depth of field is the depth of what is in focus in your image. A tiny aperture opening will bring more things into focus. Things that are both near and far away, relative to whatever you focused the lens on when you take your shot can generally be more in focus with a smaller aperture. If you want to have a narrow depth of field so that only your subject is in focus while everything else is blurred out, then you need to use a larger aperture (low f/stop number).

Next we get to the 2nd setting: shutter speed. The shutter is similar to your eyelid. The longer it stays open, the more light it lets in. If it opens and shuts really fast, then only a small amount of light gets in. If you are in bright light, then you'll likely need to use a faster shutter speed. If you are in low light, then you'll probably need to use a slower shutter speed.

Shutter speed variations do something else as well. If you want to freeze fast-moving objects, like stopping the action in sports photography, then you need a fast shutter speed. But if you want to show the blurred action of moving objects, then you need the shutter to be open for a longer time in order to pick up all the movement that you are after.

The 3rd setting is ISO. A high ISO number (1600, 3200, 6400, etc...) is like your naked eye. It is very sensitive to light, and it picks up detail very easily. You may need to squint or open and shut your eyes really quickly when it is really bright.

A low ISO number is like your eye behind sunglasses. It makes your eye less sensitive to light, so you don't have to squint and you can leave your eyes open longer in bright light. But in dim light you may not be able to see very well, so you'd need to remove your sunglasses.

ISO also has another effect on the photo. Higher ISO numbers will make photos in low light situations brighter, but it comes with a price. Higher ISO settings cause the image to have more "noise" or grainy appearance.

Everything about choosing camera settings is a trade-off. You have 3 different settings that you could adjust to make an exposure brighter or darker, and each of the 3 have side-effects. Which side-effect do you want? Which one do you NOT want? Which one can you live with if you have to, even though you'd prefer not to have it?

I start with the side-effect that I want, and then I work from there. If I am shooting sports, then I definitely want to stop fast action. That means I must have a fast shutter speed. That costs me light, so if I am not shooting in bright sunlight then I have to open up my aperture and/or move to a higher ISO setting. I go to higher ISO as a last resort, because I want to minimize noise. But once you open up your aperture all the way, if you still need more light in order to get a good exposure with a fast shutter, then you have to start boosting ISO.

If I am shooting a portrait or something and I want only my subject to be in focus while everything in the background is blurred out, then I must shoot the shot with a large aperture (low f/stop). That lets in a lot of light, so if I have fairly bright light to begin with, then I will need to shoot a low ISO and/or a faster shutter speed to keep from over-exposing the shot.

There are always more than one combination of settings that will give you a proper exposure of light in a given situation. But the side-effects will vary, depending on which combination of settings you use. It's all about the trade-offs.....

Thanks Shane. Exactly what I was looking for. Now Ill just have to read it 35 times so I'll be able to remember these key factors when I don't have someone holding my hand when shooting!

Thanks to all you other fine folks also. Big help. I definitely have a better understanding now.

[Shane]

Thanks Shane. Exactly what I was looking for. Now Ill just have to read it 35 times so I'll be able to remember these key factors when I don't have someone holding my hand when shooting!

Thanks to all you other fine folks also. Big help. I definitely have a better understanding now.

The best way to really learn it is to set your camera to Manual mode and take a bunch of pictures. First, set it to auto mode and take one picture. Take a look at the settings that the camera used. Now switch to manual mode and dial in those same settings. Take another picture. Should be identical to the auto mode pic. Now change one of your settings. Start with ISO, for example. Change it higher or lower a notch. Leave the f/stop and shutter speed the same. The only thing you changed is the ISO. See what happens to your photos when you change ISO up and down.

Now put ISO back to where you started. Take another "base" picture, just for reference. Now change f/stop up and down and see what happens.

Go back to your base settings and then start changing only the shutter speed and see what happens.

By doing this type of exercise, you start to become familiar with how you can control the outcome of your photos by changing the settings in manual mode.

[Casey]

Google DSLR simulator. There are some useful tools online to see the effects of various settings. The one I'm thinking of has a little girl with a pinwheel.

[Mike D]

Tagged as I am still learning myself.

[Snakelover]

Google DSLR simulator. There are some useful tools online to see the effects of various settings. The one I'm thinking of has a little girl with a pinwheel.

That is downright nifty!

http://camerasim.com/apps/camera-simulator/

[Sleepy]

The best way to really learn it is to set your camera to Manual mode and take a bunch of pictures. First, set it to auto mode and take one picture. Take a look at the settings that the camera used. Now switch to manual mode and dial in those same settings. Take another picture. Should be identical to the auto mode pic. Now change one of your settings. Start with ISO, for example. Change it higher or lower a notch. Leave the f/stop and shutter speed the same. The only thing you changed is the ISO. See what happens to your photos when you change ISO up and down.

Now put ISO back to where you started. Take another "base" picture, just for reference. Now change f/stop up and down and see what happens.

Go back to your base settings and then start changing only the shutter speed and see what happens.

By doing this type of exercise, you start to become familiar with how you can control the outcome of your photos by changing the settings in manual mode.

Google DSLR simulator. There are some useful tools online to see the effects of various settings. The one I'm thinking of has a little girl with a pinwheel.

That is downright nifty!

http://camerasim.com/apps/camera-simulator/

Awesome, thanks!

[Limbwalker]

That is downright nifty!

http://camerasim.com/apps/camera-simulator/

That is so cool!

But the distance slider kinda creeps me out a bit!