Lightroom displays the flash EXIF metadata in a field they call Flash. Unhappily, the value of this tag is either 'Did fire' or 'Did not fire.' This tag appears as Metadata criteria in the Library Filter bar as 'Flash States,' but one is not further enlightened by filtering on this criteria.
A simple solution is to write the camera's flash metadata to Lightroom's Keyword tags.
Perl 5 ‑ Things Your Mother Didn't Teach You About Knitting
As part of my workflow, I've been using exiftool's command‑line interface to add exposure compensation keywords to my RAW image files. I made the switch to a Perl script because I couldn't think of a way to use multiple '‑if' conditions–one for exposure compensation, the others for flash compensation (i.e., ‑if '$FlashMode =~ "Fired"')–without making multiple passes.
Flash Photography ‑ Who Knew It Would Be So Complicated?
It seems there are a zillion combinations of built‑in and external flash settings (I haven't even tried flash bracketing), so I've decided to do my 'regular' flash photography as outlined below. I'm using a Nikon D300 camera and Nikon Autofocus Speedlight SB‑800 flash. My Perl script is dependant on these flash settings for appropriate tag retrieval.
Will not use the built‑in flash on it's own.
Will use SB‑800 either in the shoe or remotely.
Will not use command dial for compensation.
When SB‑800 in shoe, will set e3 to TTL and set compensation on SB‑800.
When SB‑800 in remote mode, will set e3 to Commander Mode then choose the mode and compensation on the camera.
Note: even if [‑ ‑] is selected for [Built‑in flash] > [Mode], the built‑in flash must be raised so that monitor pre‑flashes will be emitted. The built‑in flash does not fire, but the AF‑assist illuminator lights. The AF‑assist illuminator lights are so bright I thought the built‑in flash was firing, which certainly added to my confusion. I did some research and found this: The Nikon SG‑3IR IR Panel for Camera Built‑In Flashes attaches to the camera's flash shoe, and covers and prevents the camera's built‑in flash (pre‑flash) from influencing the exposure (http://photo.net/nikon-camera-forum/00O8yc).
Tags may differ for each camera make/model. Run this command to output a list of tags to a file (one for each image), in a subfolder named 'tags':
Many, many thanks to Phil Harvey for his extraordinary patience in helping me with this—my first ever—Perl script.
How it Works
The Image::ExifTool library provides an extensible set of Perl modules to read and write meta information, accessed through the methods of the public interface (GetValue, SetNewValue, etc.). Note: some Image::ExifTool methods and modules should not be accessed directly because their interface may change with future versions (i.e., Image::ExifTool::Exif::ConvertFraction, Image::ExifTool::ShiftTime, etc.).