I've been asked a few times recently about using manual mode on a digital SLR camera. "Turn the big knob on top of the camera to M," I say, "point the camera at your subject and press the shutter halfway down. You'll see in your viewfinder if the camera thinks you are underexposing or overexposing -- there's a little indicator that will let you know."
Sometimes that's enough, but usually the next question is about what settings to start with -- as in what aperture and shutter speed to use.
Well, a while back I wrote about using the The Sunny F16 Rule. It turns out those same ideas will help you estimate exposure for shooting outside during the day. Try this:
1. Set your ISO to 400.
2. When using the "Sunny F16 Rule" you set your shutter speed to match your ISO: so set it to 1/400th of second.
3. Look at the shadows the sun is casting. If it is clear and bright, you'll probably see hard shadows, but as it gets more overcast the shadows will get softer or disappear. So:
a. if you see hard shadows, set your aperture to f/16
b. if you see soft shadows, set your aperture to f/11
c. if you see no shadows, set your aperture to f/8
d. if the light level seems even lower, set your aperture to f/5.6
That's all. Set your camera to M. Set your ISO to 400. Look at the shadows and set your aperture. Point your camera at your subject, press the shutter halfway down. Your camera may have a little triangle, or a light or another indicator that lets you know if it thinks you are over or under on your exposure. Adjust if you agree, or go with your guess. Take the shot.
Look on your viewscreen, and see if you've got it right -- and then act superior to anyone using automatic modes.