diff --git a/start_tx.sh b/start_tx.sh
index c3eb875..cd51143 100755
--- a/start_tx.sh
+++ b/start_tx.sh
@@ -92,11 +92,14 @@ sleep 10
 # Additional configuration lines you may wish to add or remove before the $CALLSIGN line may include:
 # Flip the image vertically and horizontally (e.g. if the camera is mounted upside down)
 # --vflip --hflip \
+#
 # Add a logo overlay in the bottom right of the image. This must be a transparent PNG file.
 # --logo yourlogo.png \
+#
 # Set a fixed focus position on a PiCam v3 (NOTE: The Picamv3 focus drifts with temperature - beware!!!)
 # 0.0 = Infinity
 # --lensposition 0.0 \
+#
 # Set a user-defined AutoFocus Window Area, for use wiith PiCam v3 in Autofocus Mode
 # Must be provided as x,y,w,h  , with all values between 0-1.0, where:
 # x: Starting X position of rectangle within frame, as fraction of frame width
@@ -104,7 +107,11 @@ sleep 10
 # w: Width of rectangle, as fraction of frame width
 # h: Height of rectangle, as fraction of frame height
 # e.g:
-# --afwindow 0.25,0.25,0.5,0.5
+# --afwindow 0.25,0.25,0.5,0.5 \
+#
+# Set a fixed lens offset for the PiCam v3, in dioptres. May help with autofocus in cold temperatures.
+# e.g. to offset by 1 dioptre:
+# --afoffset -1.0 \
 
 python3 tx_picamera2_gps.py \
     --rfm98w $SPIDEVICE \
diff --git a/tx/WenetPiCamera2.py b/tx/WenetPiCamera2.py
index 43cb5d6..c6deaa4 100644
--- a/tx/WenetPiCamera2.py
+++ b/tx/WenetPiCamera2.py
@@ -54,6 +54,7 @@ class WenetPiCamera2(object):
                 whitebalance = 'auto',
                 lens_position = -1,
                 af_window = None,
+                af_offset = 0,
                 temp_filename_prefix = 'picam_temp',
                 debug_ptr = None,
                 init_retries = 10
@@ -85,6 +86,7 @@ class WenetPiCamera2(object):
                         w: Width of rectangle, as fraction of frame width
                         h: Height of rectangle, as fraction of frame height
                         If not provided, the default windowing (approx centre third of width/height) will be used.
+            af_offset:  Offset the lens by a fixed dioptre. May help with autofocus during flights.
             temp_filename_prefix: prefix used for temporary files.
 
             debug_ptr:	'pointer' to a function which can handle debug messages.
@@ -103,6 +105,7 @@ class WenetPiCamera2(object):
         self.vertical_flip = vertical_flip
         self.lens_position = lens_position
         self.af_window = af_window
+        self.af_offset = af_offset
         self.af_window_rectangle = None # Calculated during init
         self.autofocus_mode = False
 
@@ -139,7 +142,20 @@ class WenetPiCamera2(object):
         except:
             pass
 
-        self.cam = Picamera2()
+        # Apply a lens offset if we have been provided one.
+        if self.af_offset != 0:
+            tuning = Picamera2.load_tuning_file("imx708.json")
+            map = Picamera2.find_tuning_algo(tuning, "rpi.af")["map"]
+            #print(map)
+            offset_hw = self.af_offset * (map[3]-map[1])/(map[2]-map[0])
+            for i in range(1, len(map), 2):
+                map[i] += offset_hw
+            #print(Picamera2.find_tuning_algo(tuning, "rpi.af")["map"])
+
+            self.cam = Picamera2(0, tuning=tuning)
+        
+        else:
+            self.cam = Picamera2()
 
         self.camera_properties = self.cam.camera_properties
 
@@ -328,6 +344,7 @@ class WenetPiCamera2(object):
         # Copy best image to target filename.
         self.debug_message("Copying image to storage with filename %s" % filename)
         os.system("cp %s %s" % (largest_pic, filename))
+
         # Clean up temporary images.
         os.system("rm %s_*.jpg" % self.temp_filename_prefix)
 
diff --git a/tx/tx_picamera2_gps.py b/tx/tx_picamera2_gps.py
index 7287a3a..bd10e4c 100644
--- a/tx/tx_picamera2_gps.py
+++ b/tx/tx_picamera2_gps.py
@@ -34,6 +34,7 @@ parser.add_argument("--resize", type=float, default=0.5, help="Resize raw image
 parser.add_argument("--whitebalance", type=str, default='daylight', help="White Balance setting: Auto, Daylight, Cloudy, Incandescent, Tungesten, Fluorescent, Indoor")
 parser.add_argument("--lensposition", type=float, default=-1.0, help="For PiCam v3, set the lens position. Default: -1 = Continuous Autofocus")
 parser.add_argument("--afwindow", type=str, default=None, help="For PiCam v3 Autofocus mode, set the AutoFocus window, x,y,w,h , in fractions of frame size. (Default: None = default)")
+parser.add_argument("--afoffset", type=float, default=0.0, help="For PiCam v3 Autofocus mode, offset the lens by this many dioptres (Default: 0 = No offset)")
 parser.add_argument("-v", "--verbose", action='store_true', default=False, help="Show additional debug info.")
 args = parser.parse_args()
 
@@ -211,7 +212,8 @@ picam = WenetPiCamera2.WenetPiCamera2(
 		horizontal_flip=args.hflip,
 		whitebalance=args.whitebalance,
 		lens_position=args.lensposition,
-		af_window=args.afwindow
+		af_window=args.afwindow,
+		af_offset=args.afoffset
 		)
 # .. and start it capturing continuously.
 picam.run(destination_directory="./tx_images/",