ISO stands for quality.
ISO stands for quality.
The ideal ISO value is the native ISO (base) value of your camera. In most cases the base ISO is 100 but some cameras start at ISO200.
Light goes through the lens and reaches your digital image sensor. If there is enough light your camera will always choose the lowest ISO possible. That is when ISO is set on automatic.
But what when we shoot indoors in a badly lid environment? Your camera will automatically raise the ISO value. This is done by amplifying (analog) the captured light. This results in more noise and more noise means less image quality.
By the way, noise is not grain.
In post processing photographers sometimes add grain after sharpening the picture to make the image less “perfect”. When you have a noisy picture your image will be less sharp and when you post process the image like lifting the shadows more color noise will be visible. That is why you always need to photograph at the lowest possible value but this is not always possible.
Sometimes you cannot use a value of ISO 100. For example when I am shooting a concert ISO values can raise up to ISO6400. Most of the time ISO is set to automatic as the amount of light on a concert can be unpredictable.
When you photograph indoors it can happen you need to use a faster shutterspeed to make sure you do not have blurry pictures (motion blur) even when using a fast lens shooting at f/1.4.
In this case you really need to raise the ISO value on your camera.
For this picture I had to raise my ISO to 2500 because their was only one small light source. To make sure I didn’t have motion blur I shot at 1/60 at 24mm. Kedist was not moving so 1/60 is perfectly fine. The lens I was using was a 24-105 f/4 at f/4. The RAW picture was post processed afterwards because even with these settings the photo was still underexposed.
Look at the color noise in the RAW image. Noise canceling software and image sensors have improved a lot over the years. There was a time when the image quality at ISO 800 was much worse compared to the excellent Sony A1 with a whopping 50MP sensor.
DXO optics has excellent denoise software (even at ISO6400 on modern cameras) but the quality will NEVER be as good when shooting at ISO100. Some photographers swear by Topaz Labs Denoise but personally I find the result not as good as the DXO software.
Denoise software and the quality of image sensors have improved a lot over the years and a lot of photographers think using high ISO values are the way to go.
Though ISO is the last parameter in the exposure triangle you should modify.
A few weeks ago I saw a youtube video of a photographer with more than a million followers photographing a model outdoors. She used ISO 800 at 1/1600 of a second!
The reactions on her post were positive and most of her followers now think using ISO 800 outside is perfectly normal. It’s not. These are the kind of videos I really hate. I have nothing against youtubers bringing great content but when you shoot with these values outdoors you don’t even understand the basics of the exposure triangle!
The correct values should have been ISO100 and a shutterspeed of 1/200. The picture would have been also razorsharp and best quality. Just lower both values by 3 stops. 800->400->200->100 and 1/1600->1/800->1/400->1/200
In real life most people do not see the difference between a sharp and a less sharp picture so why bother?
As a photographer you want the best image quality and that was ISO is all about.
There is nothing wrong using higher ISO values but only when necessary.