You will find the Guides tool in the Lens tool tab where the Crop tool is also located.
- First of all, enable the visibility of the Guides in the Viewer by selecting the Show option in the Guides tool or go to the menu and select View -> Guides to toggle them on and off. You can assign a keyboard shortcut to this command.
- Click on the + (plus) icon in the bottom-left corner to create a new guide. You will now get a couple of options to position the guide with high precision.
- First select the desired position unit (%, px, mm, cm or in) from the unit drop-down menu. Then select what edge of the image the position should be calculated from. This is done by selecting either From Top, From Left, From Right or From Bottom from the Position drop-down menu. Finally, enter the desired position value in the field to position the guide line where you want it (like 10% From Left edge).
- If you want to add another guide line, click again on the + (plus) icon in the bottom-left corner. Note how the settings will be copied from the guide settings above, making it easy to add several guides where you only have to change a single value or setting.
- You can select one of the six available grid colors to ensure that the grid will be easy to see against the image subject. You can choose between black, white, red, yellow, magenta or cyan. The selected color will be applied to all the added guide lines. Red is the default color.
The Follow Crop option will fit the guide lines inside the chosen crop and follow it as you readjust the crop. If the option is deselected, the guide lines will fit the full image regardless of the chosen crop. This can be a great way to add a visual “safe zone” along the boundaries of the image when cropping.
If you want to assign a keyboard shortcut command to toggle the visibility of the Guides on and off, select Edit -> Edit Keyboard Shortcuts… and find the Guides command. Note that you can also assign additional keyboard shortcuts to other related Guides commands under Customize Guides in the Edit Keyboard Shortcuts dialog box.