Introduced back in 2013, the Radial Filter has become my second favourite light adjustment, second to the Graduated Filter right beside it in the Develop module in Lightroom. Like the latter it can adjust almost every feature controlled in the Develop module. The advantage is its shape and ability to affect smaller portions of the image. That shape is circular or elliptical, and can vary in size from tiny to larger than the image itself. As an ellipse it can be rotated and pulled out in 4 directions for a close fit on the part of the image one wants to alter. One can feather the edges for very smooth transitions between image parts.
If two or more parts of an image require the same adjustments the Radial Filter applied to one part can be duplicated and dragged onto the other part(s).
By holding the cursor over the center of the filter area one can produce a red mask that shows exactly what area of the image is being manipulated.
By selecting the “Invert Mask” option one can have the adjustments apply only to what is outside the initial selected area. One could create a 3d effect by applying a gradual blur to what is behind the main subject, for instance.
While using the Radial Filter one can now apply the identical adjustments elsewhere in the image with the brush tool simultaneously. Handy when one wants to use the brush tool’s erase function as well to touch up adjusted areas.
Two areas that might lend themselves to special attention in an image are sunspots (even adding them) and the moon (controlling brightness, sharpness).
The Radial Filter is an easy-to-use, valuable tool in Lightroom. I recommend looking for opportunities to put it into your workflow if the image lends itself to that kind of adjustment.