The crop tool’s grid overlay is a handy feature to check the alignment of your image while cropping and rotating. In Lightroom 5, you can also show a grid on your image while you’re not working with the crop tool, too. Better yet, you can also resize this grid and change its opacity to make it nonintrusive to your other editing tasks.
Displaying The Grid
To display the grid in the Library or Develop modules, navigate to View > Loupe Overlay > Grid or use the shortcut Command + Option + O (⌥⌘O) on the Mac, or Control + Alt + O on Windows.
Changing The Grid Options
With the grid visible, you can change the size and opacity by holding down the Command key on the Mac or the Control key on Windows to bring up the overlay options.
To change the options, move your mouse pointer over either the Size or Opacity values, and adjust them by clicking and dragging the mouse left to decrease or right to increase their values.
Straightening Images With The Loupe Grid Overlay
I wish these options were also available in the crop tool’s grid, since having a variable size and opacity would make the overlay more useful for cropping and rotating. Unfortunately, when you switch to the crop tool, Lightroom will only show the crop tool’s overlay. But you can still take advantage of the adjustable features of the loupe grid overlay for straightening your images is to use the Lens Correction panel to rotate your image instead of using the crop tool. To do this, switch to the Develop module, enable the grid, and set the size and opacity. Scroll down to the Lens Correction panel and click on the Manual tab. One of the sliders in the tab is Rotate, which you can use to rotate and straighten your image using your customized grid.
The difference between doing it this way compared to using the crop tool is that the crop tool will automatically adjust the crop of the image to compensate for the rotation, where using the Rotate slider will not and you will see white in any areas that rotate outside of the frame.