Using Masks with Adjustment layers

Adjustment layers are wonderful. They allow you to make changes to your photograph without damaging the original photo.
A nice feature with adjustment layers is the fact that they come with their own masks. If you are familiar with masks you know that a mask allows you to control what part of the image you want the adjustments made to.
Here is my original photo.

 

I like the dark background but the object needs to be lighter. Below is my resulting photo. Using an adjustment layer with levels and a layer mask.

 Here are the steps I went through to create this effect.

1. I created a new adjustment layer and selected levels
2. I adjusted the midtones up by sliding the middle triangle to the left
3. I selected the mask in this adjustment layer and filled the mask to black
1. Black conceals everything
4. I painted with white to reveal the levels adjustment just on the piece in the foreground

You can see the shape of the piece showing through in white on the mask layer. This is the area that is allowed to be adjusted by levels leaving the background exactly as I wanted it.
If I accidentally over painted the white and got some of the background I simply use a black paint brush to paint it away in the layer mask.

The result is the perfect image of saving the background and just making edits to the area needed.