For those of you lucky enough to have a 1D Mark IV, here as a follow-up to my review a few days ago is another tip.
Canon by default has the “Auto Light Optimizer” set to “ON”, and this is a custom function you may well miss.
If you shoot RAW (as you really ought to), go into custom functions II, function 4, and take that off zero (0=”standard” Auto Lighting Optimizer” setting) and turn that to custom setting 3 (“Disable”).
What does ALO do to your RAW image? Nothing. And you shoot RAW. So why does it matter? Here’s why.
If you set ALO to ON, your camera will, where necessary, apply “fill light” to the data that comes from the sensor, and use the result to make its little embedded JPG. That will make dark areas lighter.
And that little embedded JPG is what you see on the back of your camera.
So when you look, you will see a well-exposed picture. Happily, you shoot more. But in fact, unbeknownst to you, the actual data is darker. You may well be underexposing the dark areas of your picture! And like me. you wonder why when you import your image into Lightroom (which does not honour that same “fill light” setting) it looks so much darker than on the camera. Or rather, you wonder why the histograms are so different (you should probably not judge exposure just by the image on the LCD).
So when you turn ALO off, the camera no longer shows you an “enhanced mini JPG”; instead, it shows something closer to the real RAW image. And if that is dark, you can fix it by adding light, not by tweaking bits (which can add noise).
UPDATE: Chuck Westfall agrees. See the comment below.