I sound like a total noob

[mybelle]

which I am, but please help me understand ISO. I've read a lot about it but can't quite grasp how it relates to exposure, aperture, and how it effects my photos. I understand the definition but not the application--if that makes sense.

I keep getting grainy results and it's driving me NUTS! (Even when I set it to auto out of frustration).

Thanks!

 

[Eventer]

Are they still coming out grainy even when your ISO is only 100?

 

[Aayria]

Hi mybelle =)

I like to think of ISO as my canvas when taking a picture. In the days of film, ISO was part of the film you bought, and you would choose your film based on what ISO you needed. For example, if you had a lot of light and didn't need to worry about low light conditions, you'd choose a film with like 100 ISO. If it was dark, you'd choose the highest ISO film you could, 800ish.

A low ISO is like a smooth, clear canvas ready to splash your light onto. A High ISO is a grainy canvas that will take the light available and make it brighter in dark situations.

In digital photography, ISO sets the stage for your exposure "triangle." You set your aperture and shutter speed, and balance them with your ISO. Generally, it's best to set the ISO as low as you can to avoid noise/grain in your pictures. But if you set it lower, you have to have the light available to use the shutter speed and aperutre you need for the picture you'd like to take.

I highly recommend reading Bryan Peterson's "Understanding Exposure."

Hope that helps!

 

[jritz]

Basically you ISO is your sensors sensitivity to light. 100 is usually the base number and each step as you go up (200, 400, 800, 1600etc) effectively doubles your exposure. The main use for ISO is to give you more light in a situation where your aperture may be maxed out, and you don't want to decrease your shutter speed and you don't have a flash.

 

[mybelle]

Are they still coming out grainy even when your ISO is only 100?

Nope, at 100 there's no grain. My son finally went down for a nap so I got more time to fiddle with my camera. The ISO was set to auto so my manual adjustments were moot. Grrr. All's well now.

Aayria--I love the canvas comparion; that helps a lot. Now I have a visual, practical application--thank you!

 

[Kerbouchard]

ISO doesn't give your sensor more light. It doesn't make the sensor more sensitive. And it definitely doesn't double your exposure.

Ok, ISO is not your camera's sensor's sensitivity to light. It is a way of amplifying the signal that is recorded by the sensor while the signal is still in it's analog form.

All circuits have noise...turn the gain up on any amp or radio and it's easy to hear the noise.

Same thing for a camera. If you have a week signal, (the data captured from a camera sensor in low light conditions) then it has to be amplified to show up within the normal range, i.e. not black. That's all well and good...the only problem is, the noise, or electrical interference gets amplified also. That is the noise(digital version) or grain(film version) that you are seeing.

Modern high end cameras have ridiculously low digital noise and very sophisticated ways of telling the difference between the actual signal and the interfering noise(usually called Noise Reduction if shooting in JPEG) and can capture images at ridiculously high amplification(ISO), but if you have a very week signal and attempt to amplify it, the Signal to Noise ratio will eventually catch up and make your picture an indistinguishable bunch of speckles.

The secret to shooting with high ISO is to make sure that you aren't asking your camera to do to much...it still needs a strong signal from the sensor so that the noise won't be so apparent, i.e. enough light, a wide enough aperture, or a slow enough shutter speed.

Yes, if you amplify the signal that the sensor receives, you can, indeed, shoot with a faster shutter speed, or lower light, or a smaller aperture, thereby reducing the signal the sensor receives and still end up with an image that appears to be the correct exposure, but that isn't part of the actual exposure that the sensor sees.

In digital cameras, there are 3 parts to exposure.
1. The amount of light available.
2. How long the shutter stays open exposing the sensor to light.
3. How large the aperture opening is letting more or less light to go in.

That is the exposure triangle.

There is, however, a fourth factor in how your image will appear in print or on screen... and that is how much you amplify the signal after the sensor records its data and before it is stored on your memory card. That is ISO. Hope this clears it up.

It is relatively easy to take a high noise ISO 400 shot and a relatively low noise ISO 1600 shot. It all depends on the signal to noise ratio. That is another reason why noise usually shows up in the shadows of an image. There wasn't much of a signal there to begin with.

 

[djacobox372]

Simply put: higher iso = brighter photos at the sacrifice of more noise/grain.

 

[jwbryson1]

If you are in a low light situation and want to take a photo, but you are unable to either (i) set a larger aperture (already at max aperture for the lens you are using, for example) or (ii) slow the shutter speed (slower shutter speeds cause camera shake and blurry photos), then you can turn UP your ISO to make the sensor more sensitive to the available light. The downside is the risk of increased grain. But, a grainy photo is better than a severely underexposed photo, IMHO.

 

[Kerbouchard]

Wow, just wow. Is there a banging a head against the table smilie?

 

[The_Traveler]

The actual activity doesn't make any difference to you.
What you need to remember is that the higher the iso, the less light is needed to make a picture so you can make the aperture smaller or the shutter speed faster.

The higher the iso, the more chance of random noise and 'grain' in your pictures.