Here are two settings on the Canon 40D that few owners know about. If you know someone with a 40D, send this along to them!
1: ISO Expansion
In normal mode, the 40D only shoots in ISOs 100-1600. Once ISO expansion is turned on, ISO 3200 is made available, denoted as ISO H. This is a HUGE help in low light situations, especially capturing action, such as football games under the lights or indoor volleyball games.
To turn it on:
Menu > Scroll over to the Custom Functions menu (the orange square with the camera) > Select C.Fn I: Exposure > Set > Scroll over to 3: ISO Expansion > Set > Select 1: On > Hit Menu to go back to the regular menu.
There you are! You can now shoot in ISO 3200! (I suggest using something like Noise Ninja in your post-processing to clean up some of the additional noise.)
2: Highlight Rendition
This little known setting improves the details in highlights. You won’t notice a difference in most shots, but it becomes wildly apparent when shooting photos with strong highlights, such a sunset lighting up a few select clouds with others in shadow. Ken Rockwell has a great writeup on this setting.
To turn it on: Menu > Scroll over to the Custom Functions menu (the orange square with the camera) > C.Fn II: Image > Set > 3: Highlight Tone Priority > Set > 1: Enable > Hit Menu to go back to the regular menu.
As Ken Rockwell points out, this setting won’t help you if you overexpose a photo, and it limits your ISO from 200-1600 if you have it on. I only turn it on when I notice a scene with strong highlights I want to get more detail in.
