Why use low ISOs?

[Bullseye]

I've seen several comments that it's ok to use ISO 1600 because of it's low noise, and others that say you shouldn't use it unless you have to. Is there really a difference in quality when using the lower speeds? I am in no way an expert, but I don't seem to see any difference. What am I missing?

[CyberDyneSystems]

Between ISO 100 and 1600 the difference is quite substantial

[Marshy]

Unless you have a 20D or above quality camera that can handle the noise generated by high iso,s the lower the iso the better but in poor light the iso needs to be raised to get a faster shutter speed .

[markubig]

i have a 300D Digital Rebel. Noise becomes noticeable at ISO800 and very bad at 1600 & 3200 (i have the hack). However, you have the 20D, and from what I've heard/read, the noise levels at ISO1600 on a 20D are not that bad. Try shooting at 3200 and maybe you will see noticeable noise. High ISO noise is one of the reasons why I want to upgrade from the 300D to the 20D. There are software filters that can take care of it, but if I can get a clean shot out of the camera, that would save me some time in post.

[CyberDyneSystems]

Granted the 20D has lower noise levels at ISO 1600 than most any other Digital,. it is still not as good as lower ISO settings.

Choosing to ignore the best possible ISO becuase the next highest might be good enough,. is just another one of the compromises that perhaps some would be willing to make,.

Like shooting jpeg,. or without a tripod etc...

But with the ISO question.. it is so simple to just adjust a dial,. I can't imagine why you would't.

[Bullseye]

It's not that I don't want to, I just need to understand the trade-off involved. What is the best possible ISO?

[cmM]

if you look hard enough, you can notice difference as far as noise even between ISO-100 and ISO-200. It's small, but it's there.
Also, you don't always want the highest shutter speed you can get, sometimes you want the lowest.

[ssim]

It's not that I don't want to, I just need to understand the trade-off involved. What is the best possible ISO?

There isn't one ISO that is best for everything. You have to change it to meet your shooting requirements. Low light will require higher ISO in order to maintain shutter speed or f-stops required to get the results you need.

As stated elsewhere here, as you move up the ISO scale, your noise will become more noticeable.

General rule of thumb that I use is to keep my ISO as low as possible and still get the shutter speed that I need to make sure the image is sharp.

[Bullseye]

Ok, that's been my normal practice anyway. Still, is noise really the only issue? No reduction in dynamic range for example? CyberDyneSystems response seems too emphatic for that.

[Redbird_xo]

High ISO picture vs. not getting the pic should be evaluated on an individual basis. If one prefers getting a noisy picture over not getting it at all, by all means use high ISO. For me personally, I mostly take close up pix of people, noisy pictures just don't cut it for me.

[CyberDyneSystems]

There are tests that say that particular ISOs have beter dynamic range...

But no,. my only concern when dialing in the lowest ISO I can get by with is noise.

For me if the subject is a moving one,. then my "lowest" ISO may be 400 if the lighting os anything other than bright afternoon... in whaich case I may be at ISO 100 or 200.

But of the subjec isn't moving,. then I'll start at 100.

Also,. I consider the ISO now as almost as much as I consider shutter speed and aperutere,.

ie: the momnet I start to stop down for DOF,.. I may start to bump the ISO to kep the shutter speed the same.

[Kinger]

I use ISO's as way to achieve fast shutter speeds, and it doesn't neccessarily need very low light to take advantage of it. For example open up this shot:

http://home.comcast.net/~king247/images/CRW_1433.jpg

This was shot at ISO 1600, with very little post proccessing to correct the color and some USM. As you can the noise is hardly noticable, this is do to exposing to the right of the histogram. I have very shacky hands so I had to use a very high shutter speed, but under the lighting conditions, I am sure that the same shot could have achieved with ISO 800 or even 400 by someone with steadier camera technique.

[Bullseye]

Ok, so bottom line is that lower ISO's may have more range, but the main issue is the possibility of noise. Sounds good to me! Considering that I absolutely hated working with anything higher than 200 when using film, it's a luxury to be able to go higher in digital format. I have to say I'm impressed with how the 1600 speed performs, and will not hesitate to use it when needed.

[tim]

Higher ISOs lose detail. With my 20D I start seeing noise at ISO 400, though not much, I find 800 fine and usually don't bother with noise reduction. ISO 1600/3200 are better than the 10D/300D, but there's still noise there that needs to be put through software to remove it.

[aam1234]

There is another point that might have been overlooked and that is how sufficient the light was. Meaning you will see more noise at dark/underexposed areas, whereas well lit photos don't have as much noise at the same high iso.