Repository: flutter
Issue: [camera][camera_avfoundation] Suspicious EXIF "FocalLengthIn35mmFilm" field value
Labels: platform-ios,p: camera,package,has reproducible steps,P2,team-ios,triaged-ios,found in release: 3.16,found in release: 3.20

### Steps to reproduce

1. Create a Flutter 3.16.9 application targetting Android and iOS
2. Set up a basic application using the camera, 
3. Ask for a medium resolution preset, create a CameraController and, immediately after initializing the controller, call `takePicture()`.
4. Read the EXIF fields of the resulting picture (source code provided below)


### Expected results

With Android 7.1.1, using a Sony Z5 device, I get

```
"EXIF FocalLength": "423/100"
```

which is the native focal length of the device. This value is correct.

On an iPhone 8, on iOS 16.7.5, I should get

```
"EXIF FocalLength": "399/100"
"EXIF FocalLengthIn35mmFilm": a value close to 26 (mm)
```


### Actual results

On iOS, using an iPhone 8, on iOS 16.7.5, I get

```
"EXIF FocalLength": "399/100"
"EXIF FocalLengthIn35mmFilm": "177"
```

177mm is just plainly wrong.

I currently have no other iOS phone to test this with, would it be possible to have somebody check if this is a bug of iOS, my device, or Flutter? It seems highly unlikely this is a Flutter bug, but this issue is nowhere to be found on Apple forums (there is not a single place on the web where this value seems out of place just like the way it is in this bug report) and there might be something fishy going on.

EDIT: Note that, on iOS, calculating the 35mm focal length is very tricky. The EXIF value described here is handy for this purpose.

### Code sample

<details open><summary>Code sample</summary>

Use this code to take a picture and the EXIF fields;

pubspec.yaml:

```dart
  exif: ^3.1.4
```
Source code:

```dart
    import 'package:exif/exif.dart';
    [...]

        final cameras = await availableCameras();
        // On the iPhone 8, there's only 1 camera with a back facing lens, and that's the first one.
        // It is the same on my Sony Z5 device
        final cameraDescription = cameras[0];

        cameraController = CameraController(
            cameraDescription, ResolutionPreset.medium,
            enableAudio: false, imageFormatGroup: ImageFormatGroup.yuv420);

        await cameraController.initialize();

    // Do this immediately after calling CameraController.initialize().
    XFile xFile = await cameraController.takePicture();
    final fileBytes = await xFile.readAsBytes();
    final data = await readExifFromBytes(fileBytes);
    for (final entry in data.entries) {
      print("${entry.key}: ${entry.value}");
    }

    // look up the "EXIF FocalLengthIn35mmFilm" value here
```

</details>


### Screenshots or Video

<details open>
<summary>Screenshots / Video demonstration</summary>

[Upload media here]

</details>


### Logs

<details open><summary>Logs</summary>

```console
[Paste your logs here]
```

</details>


### Flutter Doctor output

<details open><summary>Doctor output</summary>

```console
[√] Flutter (Channel stable, 3.16.9, on Microsoft Windows [version 10.0.22000.2538], locale fr-FR)
    • Flutter version 3.16.9 on channel stable at C:\Users\andy\Documents\flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 41456452f2 (11 days ago), 2024-01-25 10:06:23 -0800
    • Engine revision f40e976bed
    • Dart version 3.2.6
    • DevTools version 2.28.5

[√] Windows Version (Installed version of Windows is version 10 or higher)

[√] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
    • Android SDK at C:\Users\andy\AppData\Local\Android\sdk
    • Platform android-34, build-tools 34.0.0
    • Java binary at: C:\Program Files\Android\Android Studio\jbr\bin\java
    • Java version OpenJDK Runtime Environment (build 17.0.6+0-b2043.56-10027231)
    • All Android licenses accepted.

[√] Chrome - develop for the web
    • Chrome at C:\Program Files\Google\Chrome\Application\chrome.exe

[√] Visual Studio - develop Windows apps (Visual Studio Community 2022 17.0.2)
    • Visual Studio at C:\Program Files\Microsoft Visual Studio\2022\Community
    • Visual Studio Community 2022 version 17.0.31919.166
    • Windows 10 SDK version 10.0.19041.0

[√] Android Studio (version 2022.2)
    • Android Studio at C:\Users\andy\Documents\Applications\android-studio
    • Flutter plugin can be installed from:
       https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
       https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 11.0.15+0-b2043.56-9505619)

[√] Android Studio (version 2022.3)
    • Android Studio at C:\Program Files\Android\Android Studio
    • Flutter plugin can be installed from:
       https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
       https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 17.0.6+0-b2043.56-10027231)

[√] IntelliJ IDEA Community Edition (version 2021.3)
    • IntelliJ at C:\Users\andy\Documents\Applications\IntelliJ
    • Flutter plugin can be installed from:
       https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
       https://plugins.jetbrains.com/plugin/6351-dart

[√] VS Code (version 1.86.0)
    • VS Code at C:\Users\andy\AppData\Local\Programs\Microsoft VS Code
    • Flutter extension version 3.82.0

[√] Connected device (4 available)
    • E5823 (mobile)    • CB5A28LMYH • android-arm64  • Android 7.1.1 (API 25)
    • Windows (desktop) • windows    • windows-x64    • Microsoft Windows [version 10.0.22000.2538]
    • Chrome (web)      • chrome     • web-javascript • Google Chrome 121.0.6167.140
    • Edge (web)        • edge       • web-javascript • Microsoft Edge 121.0.2277.98

[√] Network resources
    • All expected network resources are available.

• No issues found!
```

</details>