I mention a number of shortcuts that are new to the Radial Filter (J) in this video (Adobe Photoshop: Favorite Features for Photographers), but thought that it might be handy to also include them in list form:
• The Shift key will constrain the Radial Filter to a circle.
• Tapping the “V” key will toggle the overlay of the Radial Filter interface (bounding box).
• While dragging one of the four handles of an existing Radial Filter to resize it, press the Shift key to preserve the aspect ratio of the ellipse.
• While dragging the boundary of an existing Radial Filter to rotate it, press the Shift key to snap the rotation to 15-degree increments.
• While dragging to create a new Radial Filter, press and hold the Space bar to move the ellipse; release the Space bar to resume defining the shape of the new Radial Filter.
• While dragging inside of an existing Radial Filter to move it, press the Shift key to constrain the movement to the horizontal or vertical direction.
• You can drag a Radial Filter beyond the image area.
• While an existing Radial Filter is selected, press the Delete key to delete the Radial Filter.
• Double-click in the image area to set the bounding box of the Radial filter to the image bounds.
• Double-click inside of an existing Radial Filter to expand the bounding box of the Radial Filter to the image bounds.
• Command + Option -drag (Mac) | Control + Alt -drag (Win) to duplicate the Radial Filter.
• While an existing Radial Filter is selected, press the X key to toggle the effect direction from outside to inside.