What focal length ARKit uses?

Hello,

I'm curious if ARKit uses a fixed focal length across all devices?

It does not, but you can determine the focal length at runtime:

    func session(_ session: ARSession, didUpdate frame: ARFrame) {
        
        let focalLengthKey = kCGImagePropertyExifFocalLength as String
        let focalLength = frame.exifData[focalLengthKey] as! NSNumber
        
        print(focalLength.floatValue)
    }

You probably need kCGImagePropertyExifFocalLenIn35mmFilm , rather than kCGImagePropertyExifFocalLength, if you want to try to interpret the value that you get back in a way tha is device-independent. (Or, maybe there is now an actual field-of-view angle property? There wasn't last time I looked at CGImages from PHPhotoLibrary.)

exifData is only available in iOS 16.0+

For a pre-iOS 16.0 solution, the focal length has always been part of the intrinsicsMatrix, which you can get from the ARCamera.