ISO 800+ -- high noise

John Deerfield wrote:

mostlyboringphotog wrote:

John Deerfield wrote:

It's a difficult question to answer. First, please understand that your camera, any camera, is simply a tool used to record an exposure. A camera records light. This concept is so very important to understand. Light is a form of energy. This energy strikes a camera sensor (or film emulsion in the days of film). When you raise the ISO you are NOT getting more light onto the sensor (and light is the signal). You are merely instructing the camera to amplify the signal (light) already present. Basic electronics: amplifying a signal means an amplification of the noise in that signal. Essentially, in low light, you have far less signal. It is this lack of signal that is creating the noise. You can test this by taking a picture in bright light (outdoors at noon on a sunny day) at a high ISO: you probably won't have much (if any) noise. Why? Because there is plenty of signal (light) hitting the sensor. - bold added

Above is somewhat confusing - you cannot use high ISO if you have plenty of lights.

Why not?

Because you will blow the high lights as in over exposed. If you keep the image brightness the same with high ISO, that means you are stopping down and/or using faster shutter speed to reduce the plenty of light to very little light.

Even if there is plenty of light, in order to use high ISO and not over expose the image, f/stop and shutter speed to reduce the plenty of light to "not so plenty" light

Yes, the exposure "equation" must be balanced so-to-speak. Which in turn means that you can use a high ISO with a lot of light.

If you use high ISO, it mean you are balancing the exposure equation to be "little amount of light".

Of course, the idea is not to use high ISO if there is plenty of light.

Fundamentally, I might say the idea is to get the desired exposure. As an example, I might be shooting in a high intensity of light thus able to shoot at ISO 100. However, perhaps I am shooting sports and the shutter speed is slower than I would like at ISO 100. How can I get a faster shutter speed? Raise the ISO. With the whole being that noise from a high ISO taken when there is plenty of light (signal) will be a LOT different than noise from that same high ISO taken when there is far less light.