diff --git a/contrib/fujifilm_dynamic_range.lua b/contrib/fujifilm_dynamic_range.lua
index 5ce8fc0..d5dee9b 100644
--- a/contrib/fujifilm_dynamic_range.lua
+++ b/contrib/fujifilm_dynamic_range.lua
@@ -28,6 +28,33 @@ Dependencies:
 
 Based upon fujifilm_ratings by Ben Mendis
 
+The relevant tag is RawExposureBias (0x9650). This appears to
+represent the shift in EV for the chosen DR setting (whether manual or
+automatic). Note that even at 100DR ("standard") there is an EV shift:
+
+100 DR -> -0.72 EV
+200 DR -> -1.72 EV
+400 DR -> -2.72 EV
+
+The ideal would be to use exiv2 to read this tag, as this is the same
+code which darktable import uses. Unfortunately, exiv2 as of v0.27.3
+can't read this tag. As it is encoded as a 4-byte ratio of two signed
+shorts -- a novel data type -- it will require some attention to fix
+this.
+
+There is an exiv2-readable DevelopmentDynamicRange tag which maps to
+RawExposureBias as above.  DevelopmentDynamicRange is only present
+when tag DynamicRangeSetting (0x1402) is Manual/Raw (0x0001). When it
+is Auto (0x0000), the equivalent data is tag AutoDynamicRange
+(0x140b). But exiv2 currently can't read that tag either.
+
+Hence for now this code uses exiftool to read RawExposureBias, as a
+more general solution. As exiftool is approx. 10x slower than exiv2
+(Perl vs. C++), this may slow large imports.
+
+These tags have been checked on a Fujifilm X100S and X100V. Other
+cameras may behave in other ways.
+
 --]]
 
 local dt = require "darktable"
@@ -44,25 +71,25 @@ local function _(msgid)
 end
 
 local function detect_dynamic_range(event, image)
-	-- exiftool knows about the RawExposureBias tag, unlike exiv2, but it is also 10x slower
 	if not df.check_if_bin_exists("exiftool") then
 		dt.print_error(_("exiftool not found"))
 		return
 	end
 	local RAF_filename = df.sanitize_filename(tostring(image))
-	local command = "exiftool -RawExposureBias " .. RAF_filename
+	-- without -n flag, exiftool will round to the nearest tenth
+	local command = "exiftool -RawExposureBias -n -t " .. RAF_filename
 	dt.print_error(command)
 	output = io.popen(command)
 	local raf_result = output:read("*all")
 	output:close()
 	if string.len(raf_result) > 0 then
-		raf_result = string.gsub(raf_result, "^Raw Exposure Bias.-([%d%.%-]+)", "%1")
+		raf_result = string.match(raf_result, "\t(.*)")
 		if image.exif_exposure_bias ~= image.exif_exposure_bias then
 			-- is NAN (this is unlikely as RAFs should have ExposureBiasValue set)
 			image.exif_exposure_bias = 0
 		end
 		-- this should be auto-applied if plugins/darkroom/workflow is scene-referred
-		-- FIXME: scene-referred workflow pushes exposure up 0.5 EV, but DR100 pushes up 0.7 EV -- should reduce this by 0.5 EV?
+		-- note that scene-referred workflow exposure preset also pushes exposure up by 0.5 EV
 		image.exif_exposure_bias = image.exif_exposure_bias + tonumber(raf_result)
 		dt.print_error(_("Using RAF exposure bias: ") .. tostring(raf_result))
 	end