To use the Lightroom 3 adjustment brush, first locate it in the Develop module
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Now open a photo within the Develop module,
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Then select the Adjustment Brush tool, which looks like a circle with a rod coming out of its right hand side.
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Then choose the size and type of the Adjustment Brush
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Finally drag it to the photo and move it around the area you want to adjust.
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The Mask button changes to Edit and you can now use the Effect sliders for further manipulation.
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