Wow, This is the conversation I have been waiting for and the explanations "I thought" I needed to better understandexposure and and its realtionship with ISO and noise. Unfortunately,I nowconsider myself at least 3 stops dumber than I was when I started reading this string. Let me see if I have the basics right:


1. High ISO (up to 1600) doesn't cause noise in and of itself--


2. Use of high ISO in the wrong situation can result in noise---


3. If correctly exposed, High ISO results in less noise butcan result in blown highlights--


4. I have erroneously compared high ISO digital to high ASA film -- what was "grainy" in film does not neccesarilymean noise in digital.


Please correct or confirm these assumptions.


Now---the big question----


I normally shoot wildlife, landscape and nature with a 50d and a 100-400L or a 24-105 L (70-200 f2.8L IS is comming). I do prefer shooting within 30 minutes of sunrise or sunset---but many times I find myself in broad daylight and hopefully adjust accordingly. I normally base my settings on desired effect; i.e. Faster shutter for motion control, narrow aperture for DOF etc ---and I set ISO on lowest possible for the shooting situation----What is the error with my method of set-up.


Note--As you have probably already summised, I have discovered that sometimes I get noise when it is unexpected.


Your response is greatly appreciated,





Bob