ISO's for Dummies

[mcgrawfan]

Can someone please explain in simple terms what ISO's are and when higher and lower numbers are better?
Thanks!

 

[wenrob]

I tried to post this earlier but the DIS had some kind of cramp and wouldn't load.

ISO is what makes your camera sensitive to light. So in a nutshell if you have plenty of light you'd use a low ISO like 200. If you have a low light situation you would want to up your ISO. So say inside you'd want to start at 400 and go up from there. Outside in the daylight you'd start at 200 (or 100 depending on your camera's functions) and go from there.

Now that's the simple answer. You also have to consider your aperture and shutter speed and how to get them to work with your ISO depending on the type of photo you want. Do you want to freeze action? Up your ISO and open up(lower #s) your ap to get your shutter speed up. If you want to slow your shutter speed and get a longer exposure (think fireworks or night shots) you'd lower your ISO and close down your ap (higher #s) to get the right speed to expose for a longer length of time. And then there are all the variables in between! It really depends on what look you want and your lighting situation to decide how you'll make all three work together. The best advice I can give is to take the same photo in different combos and compare them. It seems confusing now but eventually it'll just come together.

 

[disneyboy2003]

wenrob is correct. ISO is one part of the "exposure triangle". To get the correct exposure for any photo, you need to take into account (1) shutter speed, (2) aperture, and (3) ISO. Each of these 3 components affect the others.

ISO basically is the "sensitivity" of the camera's sensor to light. The higher the ISO, the more sensitive the sensor is to light. You would use higher ISOs when you have a low-light scene, so that your sensor is more sensitive to what little light is out there.

Sports photographers will also use higher ISOs so that they can, in turn, use faster shutter speeds to capture the action.

Why not just use high ISOs all the time? As with everything in photography, there's always a catch. The higher the ISO, the more "noise" or "grain" you'll see in your photos. These are random specks that appear all throughout a high-ISO photo.

Why not just use low ISOs all the time to avoid "noisy" photos? When you use low ISOs, your sensor's "not as sensitive", so you'll need slower shutter speeds (risk of blurry photos) or larger apertures (more expensive lenses, not as much depth of field). However, if your camera's on a tripod and you're doing landscape photography, you can easily use low ISOs, slow shutter speeds, and smaller apertures.

So the trick is figuring out the lowest ISO you can get away with for each scene. You can read more about ISO in any basic digital photography book. Hope that helps!

 

[paleduck]

gds

 

[seashoreCM]

Most of the time outdoors in daylight ISO 100 is best.

Under changeable skies or with some shots in the shade outdoors you may need ISO 200, you can leave it at ISO 200 to avoid remembering to change it a lot.

Indoors with a point and shoot you may need ISO 400 or higher.

You will often be warned of the need for a higher ISO when the camera shake or slow shutter indicator comes on in the viewfinder.

With a tripod and still life subjects you can go back to ISO 100 for less grainy pictures.

 

[pjacobi]

Bryan Peterson's "Understanding Exposure" links ISO, f/stop and shutter speed as the three points of the exposure triangle.

Check it out at your local book store...


-Paul

 

[pjacobi]

If you still think in ASA and DIN, instead of ISO, then you might be an old fart...like me!

Congratulations if you are too young to have ever heard of ASA or DIN.

-Paul

 

[seashoreCM]

(ASA numbers and ISO numbers are the same.)

 

[MarkBarbieri]

ISO is the International Organization for Standardization. One can assume that it was created by dyslectics. There are lots of ISO numbers. ISO 9660 is a filesystem standard for CDs. ISO 9000 is a family of quality management standards.

What you are probably interested in is ISO 12232:2006. That's the ISO standard for measuring exposure with digital cameras. There are different ISO standards for color negative film used for reflective prints (ISO 5800:1987), motion picture film, slide film, and others.

ISO 12232:2006 allows for 5 different ways to determine the ISO number. It's not much of a standard as it allows each manufacturer to use the Recommended Exposure Index technique, which basically allows them to pick whatever values they think look best.

Basically, it's just a scale that measures how sensitive your camera is to light. Lower numbers mean that it is less sensitive. Higher numbers mean that it is more sensitive. The scale is linear, so when the ISO value doubles, you need only half as much light to get the same exposure.

Even though manufacturers are free to adjust the scale to their liking, people have common conceptions about how much light is needed for each ISO level, so the levels are reasonably consistent. It's not uncommon to see them vary by a third or even by half, but you won't see ISO 100 from one manufacturer exposing like ISO 400 from another.

My approach is to set my ISO based on my conditions. I go with 100 when I am in bright sunlight. I switch to 200 when it is lightly overcast. I use 400 when it is very cloudy or I am in a well lit indoor location. I use 800 when I am in an indoor location that is not too bright. I use 1600 when I am in a location with subdued lighting (like a nice restaurant).

As a general rule, it is best to use the lowest ISO possible. Higher ISO settings result in more noise (graininess). While I am shooting, I set my aperture and shutter speed based on creative needs. For example, I might use aperture priority mode and a wide aperture for a portrait shot. I might use a narrower aperture and a long shutter speed for a fireworks shot. If I can consistently get faster shutter speeds than I need, I lower my ISO to improve my picture quality. If I am struggling to get a shutter speed fast enough for my needs, I increase my ISO. It's better to have a noisy picture than a picture that is blurry because the shutter speed was too low.

The ISO based on lighting settings I mentioned are just guidelines assuming that you are handholding pictures of limited activity. If you are shooting rapidly moving subjects, you may want a higher ISO so that you can get faster shutter speeds. If you are shooting non-moving subjects with a tripod, you may want to use your best ISO, which is usually your lowest normal ISO.

When you increase the ISO, the camera increases the "gain". It's a bit like turning up the volume on your radio. It makes dark pictures brighter. Unfortunately, it also makes "noise" brighter as well.

 

[boBQuincy]

When you increase the ISO, the camera increases the "gain". It's a bit like turning up the volume on your radio. It makes dark pictures brighter. Unfortunately, it also makes "noise" brighter as well.

That is exactly what happens! The sensor turns light into electricity, which is amplified and fed into the processor. The amplifier does not distinguish between signal and noise, amplifying them both. As amplification (ISO) increases so does noise, until we have as much noise as signal (actually the camera stops well before that point).

 

[seashoreCM]

When you increase the ISO, the camera increases the "gain". It's a bit like turning up the volume on your radio. It makes dark pictures brighter. Unfortunately, it also makes "noise" brighter as well.

That's all?

You mean I can instead tweak an underexposed picture later in my computer (Photoshop, etc.)? Increasing the brightness and contrast there and get the same results compared with taking another shot with a higher ISO (as in bracketing the exposure)?

 

[ThurlFan]

That's all?

You mean I can instead tweak an underexposed picture later in my computer (Photoshop, etc.)? Increasing the brightness and contrast there and get the same results compared with taking another shot with a higher ISO (as in bracketing the exposure)?

Not really. If your ISO is too high, some overexposed portions of the picture may go to pure white, and you can never get back the original shades in that area. Conversely, with ISO too low, you can end up with darker regions going completely black and never be able to recover the detail no matter how much you process it after the fact. There's a certain amount of forgiveness - if you shoot one setting off from ideal (400 when it should have been 200) but it's not always enough. Also, if you set your ISO too low your action shots can blur, which is also nonrecoverable.

 

[boBQuincy]

That's all?

You mean I can instead tweak an underexposed picture later in my computer (Photoshop, etc.)? Increasing the brightness and contrast there and get the same results compared with taking another shot with a higher ISO (as in bracketing the exposure)?

Not exactly, there is a difference between amplifying a signal (and the noise) and changing the levels. Once the signal is digitized there are only so many levels, increasing brightness & contrast deletes some of the levels. By boosting the amplification before digitizing we still maintain all the levels (even though the lower levels may be mostly noise).
It is somewhat similar to the difference between optical and digital zoom.

 

[Bstanley]

Once the signal is digitized there are only so many levels

mcgraw fan

I didn't notice what type of camera you are using, but IF your camera is capable of storing the images as 'RAW' files as well as 'JPEG' files you can get access to additional levels of brightness. RAW files are still limited, but less so than JPEG files since JPEG files are the digitized image after it has passed through the camera's processor and are much more limited in colors and brightness levels compared to a RAW file.

Dealing with RAW files adds to the complexity of dealing with the files but does give you more data that can help in getting a good picture through post processing.