The Canon 7D has many different possibilities for adjusting exposure. The most basic mode of operation, with full control over every aspect of exposure, is Manual (M) operation.
To gain access to Manual mode, see page 102 of the User Manual. (You can also download a copy of the user manual here.)
After you enter Manual mode, make sure to set the appropriate ISO, depending upon lighting conditions and intent. Looking into the viewfinder, in the lower left you should see a linear scale reading from -3, on the left, to a +3 on the right. You should also see a large tick mark in the center, and a moving Exposure Level Mark underneath of the scale.
Ideally, if you are dealing with a neutral toned subject, like an 18 percent gray card, you will want to center the Exposure Level Mark directly in the center of the scale. If you use the palm of your hand, you'll want that mark about 2/3rd stop over center. Adjust both the aperture and the shutter speed until you achieve the appropriate setting on the Exposure Level Mark underneath of the scale.
Take a sample capture and review the image with the histogram turned on and in RGB mode. Ideally, none of the RGB scales of the histogram should be out of range (i.e. overexposed to the point of clipping or underexposed to the point of crushing relevant shadow detail.) If you need to make a choice, it's usually best to avoid overexposing any important subject matter on any color channel, R, G, or B.
If your scene is low dynamic range, then it's best to "expose-to-the-right", for the reasons mentioned in this article:
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To gain access to Manual mode, see page 102 of the User Manual. (You can also download a copy of the user manual here.)
After you enter Manual mode, make sure to set the appropriate ISO, depending upon lighting conditions and intent. Looking into the viewfinder, in the lower left you should see a linear scale reading from -3, on the left, to a +3 on the right. You should also see a large tick mark in the center, and a moving Exposure Level Mark underneath of the scale.
Ideally, if you are dealing with a neutral toned subject, like an 18 percent gray card, you will want to center the Exposure Level Mark directly in the center of the scale. If you use the palm of your hand, you'll want that mark about 2/3rd stop over center. Adjust both the aperture and the shutter speed until you achieve the appropriate setting on the Exposure Level Mark underneath of the scale.
Take a sample capture and review the image with the histogram turned on and in RGB mode. Ideally, none of the RGB scales of the histogram should be out of range (i.e. overexposed to the point of clipping or underexposed to the point of crushing relevant shadow detail.) If you need to make a choice, it's usually best to avoid overexposing any important subject matter on any color channel, R, G, or B.
If your scene is low dynamic range, then it's best to "expose-to-the-right", for the reasons mentioned in this article:
http://www.luminous-landscape.com/tutorials/expose-right.shtml
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