Help me understand ISO - it's confusing the hell out of me?

Primarily being a Landscape photographer, I would agree with your choice of a tripod over ISO. Am I afraiid of ISO, No, I've used up to ISO 1600 on landscapes when the situation arises. But I don't when I don't.

Will things like what lightspeed suggests happen? Absolutely, that's why you have a brain and a choice of ISO's and you use what you need when you need.

When I am shooting Concerts, I use the crap out of ISO...sooo
 
Good ISO 800 colour neg film these days, like Portra 800, has very low graininess unlike ISO 800 of a decade or so ago (it isn't actually grain that you see, so it is called 'graininess' because it only looks like grain). You will probably find that if you have a tripod you can keep the ISO down to 200 or less for landscape photography, particularly with small format cameras (ie 35 mm and below). Even hand held, which is how I shoot landscape with small format (if I'm going to carry a tripod I may as well shoot medium or large format), I hardly ever need to go above ISO 400 when the sun is over the horizon. Look at how much great landscape work the Nat Geo photographers did with ISO 25 and 64 film.

If you do use a tripod you might find that a little motion blur of leaves and branches etc gives a good representation of how the world actually was at the time, or you may not. In practice it may not matter much because even with low ISOs exposure times never get very long on small format during the daylight hours - you usually have to use an ND filter if you want motion blur, and some people do want motion blur of course.

The best way is to try higher ISOs and see for yourself.
 
If noise and grain fall under the category "unwanted artefacts" I think we will agree on the category LOL

This brings up a question for me. In the film days we always had grain, the size of which depended on the film used. But with digital, is there always noise? I don't see any in my images but is that because it gets so small as to almost not being there, kind of like with 25 ASA film?



KmH said:
Actually, ... O setting.

Lol this is the kind of thing that confused the crap out of me when I was starting out. I would ask "what is ISO in terms of exposure triangle" and then a mountain of technical jargon and I could only answer "uuh thanks..."

I agree. Sometimes, especially with noobs, more is not better. I see this happening here all the time and I think it can confuse people more than it helps them.



It confuses me somewhat. As I read it I asked myself: What has the room size got to do with it? Why is the cassette recording at the wrong level? Do you mean the mic was a long way from the sound and the mic amp wasn't turned up? What is tape hiss analogous to? (Why was a cassette chosen?) Why didn't they use Dolby? (that last one's not serious). Isn't the analogy much simpler: the microphone has internal, self-generated noise (that is independent of the sound arriving at the mic); the quieter the sound being recorded the more the mic amp has to be turned up to reach the standard recording level, so the more the mic's own noise is amplified.

Well, my explination of DIGITAL ISO relates to listening to your home stereo system.

When you first turn on the stereo, and have NO music playing, the stereo is pretty quiet. But, if you turn the volume all the way up (increase amplification), you will hear a HISS, and that is NOISE!

So now imagine listening to a cassette recording made in a big room. You have to turn the volume way up to be able to hear what happens in the room. But, you gain a whole lot of hiss in the process. The key here, is the ratio of the "signal" to the noise. You, in this case have a very underexposed situation, with a very low signal to noise ratio. The low signal relates to a dark scene, and the high noise relates to all that hiss created by the amp being turned all the way up.

But now think about playing a CD. You can turn the volume control way back down, because have a properly exposed signal reaching the amplifier, and it doesnt need all that extra gain, creating hiss. You also have a much better signal to noise ratio; loud signal (lots of light) and hardly any noise, very low amplification.

Of course, you can have too much of a good thing also, and overload the amp by putting too much into it, aka overexposing.

This is probably over simplified, but it has helped several people I have worked with understand the process a little better. Hope it helps.

I don't know if this is oversimplified but I'm not sure how it helps a noob (unless maybe he is in the music business) understand noise in photography. I also agree with Helen's questions. For example, why would the mike be so far away that you have to raise the input level to the point of hiss?

Also when you say, "When you first turn on the stereo, and have NO music playing, the stereo is pretty quiet. But, if you turn the volume all the way up (increase amplification), you will hear a HISS, and that is NOISE!," are we talking about turning up the volume when there is no music? Because, frankly, that is exactly the first thing I do when checking out an amp. And if there is any hiss/noise, I move on to the next one. Believe me my amps do not make noise when they don't receive a signal.
 

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