Trying to get a better understanding of metering. Often hear "meter off the sky" or "meter off the hand". I'm trying to understand how this is accomplished? Example - I have my camera set to "spot" metering, and I point the camera to the sky - Is the goal to press the shutter halfway, and adjust aperture/shutter speed/iso until exposure is balanced? I guess the key is understanding what part of the photo you want exposed correctly, I'm simply challenged in understanding what gives you the meter reading. Do you meter in manual mode or in Shutter/Aperture Priority?
Do you prefer spot or matrix metering? Is there one the gives better results over the other?
Thanks for the help!
KmH - your links always help... I'm open to suggestions!
First tip.... pick up the book Understanding Exposure by Brian Peterson. Awesome read.
You have the basic understanding. You meter a scene (regardless of which mode) and in M (Manual) set the ISO, aperture and shutter to where you want them to get the desired exposure (which is usually in the middle). If you are in aperture (AV for Canon) or shutter (TV for Canon), then you are only controlling either the aperture or the shutter to get a well exposure (ie middle of the meter) image.
Ex: Lets say your are set in Manual mode, aperture f/5.6 and 1/200 shutter. You half press the shutter, the camera takes a meter reading. If the line is to the left of the meter, you are under exposed. So you have to let more light in to get a well exposed image. You can either open the aperture more (f/4.0, f/2.8,..) or slow the shutter down (1/100, 1/60,...). You have full control. If you know that you MUST stay at aperture f/5.6, then you adjust the shutter only.
Ex: Lets say you are in AV (aperture) mode. You have the aperture set to f/5.6. You half press the shutter and the meter reading will have the line in the middle and display the proper shutter speed for you to get a well exposed image. Say it gives 1/60. If you were to click, image well exposed. If however you want an aperture of f/11, you adjust the aperture, half click again, your shutter will now read 1/15. This might be a bit too slow for you. This is where ISO can come into play. If you must have f/11 and you are at 1/15 and say ISO 100, you can up the ISO to 400, which will give you 2 more stops of light... so your shutter is back up to 1/60. Why not always shoot high ISO? High ISO creates noise in the image. Not all cameras are good at handling noise. ISO 800 should be fine in most modern day cameras. But if you want to get no noise at ISO 3200 or 6400, you are looking at the full frame cameras (Canon 5D2, Nikon D700).
The logic is to normally keep your ISO low, adjust shutter and aperture, and when you have to, up the ISO.
Hope that's making sense.
For the various modes you can meter, depends on what you are looking to do. Alot of people stay in the Matrix or Evaluative metering. Why? This takes into account the entire scene to give you the meter reading to let you know if you are well exposed or not. In some cases, where the light can vary greatly, you may want to use spot metering. This means that the meter reading will be taken around that one little spot. So you can point the camera at what you want nicely exposed, half press, it gives a reading. You adjust your settings according. Then you can recompose the image and shoot and that part you spot metered on will be well exposed.
My day to day (these days) is alot of concert photography. When I shoot a low light shot, I use spot metering. I put the spot on the singers face and always ensure that the face is well exposed. The rest? What ever happens happens, light changes constantly. If I were to do a Matrix or Evaluative metering, it would look at the whole scene, which the vast majority is dark, and give me a weirdly exposed image.
I also shoot in Manual mode only. Again, with the changing lights, if I was in AV set to f/2.8, for one shot, the shutter may be 1/1000 and for the next 1/15. No control. 1/15 will have way too much blur. In manual, I can set for the right exposed (based on the singer's face) and have consistent results in my images.
Appreciate the answers, and the book recommendation - I've seen it mentioned a number of times... maybe time to grab a copy. I ask about metering, as I'm finding that I often underexpose my photos. 
