diff --git a/opensfm/exif.py b/opensfm/exif.py
index 2205007a8..228caf229 100644
--- a/opensfm/exif.py
+++ b/opensfm/exif.py
@@ -3,6 +3,7 @@
 import datetime
 import logging
 from codecs import decode, encode
+import math
 from typing import Any, BinaryIO, Callable, Dict, List, Optional, Tuple, Union
 
 import exifread
@@ -60,14 +61,42 @@ def get_tag_as_float(tags: Dict[str, Any], key: str, index: int = 0) -> Optional
         return None
 
 
+def focal35_to_focal_ratio(
+    focal35_or_ratio: float, width: int, height: int, inverse=False
+) -> float:
+    """
+    Convert focal length in 35mm film equivalent to focal ratio (and vice versa).
+    We follow https://en.wikipedia.org/wiki/35_mm_equivalent_focal_length
+    """
+    image_ratio = float(max(width, height)) / min(width, height)
+    is_32 = math.fabs(image_ratio - 3.0 / 2.0)
+    is_43 = math.fabs(image_ratio - 4.0 / 3.0)
+    if is_32 < is_43:
+        # 3:2 aspect ratio : use 36mm for 35mm film
+        film_width = 36.0
+        if inverse:
+            return focal35_or_ratio * film_width
+        else:
+            return focal35_or_ratio / film_width
+    else:
+        # 4:3 aspect ratio : use 34mm for 35mm film
+        film_width = 34
+        if inverse:
+            return focal35_or_ratio * film_width
+        else:
+            return focal35_or_ratio / film_width
+
+
 def compute_focal(
+    pixel_width: int,
+    pixel_height: int,
     focal_35: Optional[float],
     focal: Optional[float],
     sensor_width: Optional[float],
     sensor_string: Optional[str],
 ) -> Tuple[float, float]:
     if focal_35 is not None and focal_35 > 0:
-        focal_ratio = focal_35 / 36.0  # 35mm film produces 36x24mm pictures.
+        focal_ratio = focal35_to_focal_ratio(focal_35, pixel_width, pixel_height)
     else:
         if not sensor_width:
             sensor_width = (
@@ -75,7 +104,9 @@ def compute_focal(
             )
         if sensor_width and focal:
             focal_ratio = focal / sensor_width
-            focal_35 = 36.0 * focal_ratio
+            focal_35 = focal35_to_focal_ratio(
+                focal, pixel_width, pixel_height, inverse=True
+            )
         else:
             focal_35 = 0.0
             focal_ratio = 0.0
@@ -248,7 +279,10 @@ def extract_projection_type(self) -> str:
 
     def extract_focal(self) -> Tuple[float, float]:
         make, model = self.extract_make(), self.extract_model()
+        width, height = self.extract_image_size()
         focal_35, focal_ratio = compute_focal(
+            width,
+            height,
             get_tag_as_float(self.tags, "EXIF FocalLengthIn35mmFilm"),
             get_tag_as_float(self.tags, "EXIF FocalLength"),
             self.extract_sensor_width(),
@@ -636,7 +670,13 @@ def extract_exif(self) -> Dict[str, Any]:
 
 def hard_coded_calibration(exif: Dict[str, Any]) -> Optional[Dict[str, Any]]:
     focal = exif["focal_ratio"]
-    fmm35 = int(round(focal * 36.0))
+    fmm35 = int(
+        round(
+            focal35_to_focal_ratio(
+                focal, int(exif["width"]), int(exif["height"]), inverse=True
+            )
+        )
+    )
     make = exif["make"].strip().lower()
     model = exif["model"].strip().lower()
     raw_calibrations = camera_calibration()[0]