iOS Camera focus value

Question

Is there any way to get the focus value from iPhone camera with autofocus?

I want to use this data to calculate the distance from iPhone to an object in focus.

Answer 1

Obviously this is an old question, but as there is an option to get a "lense value" since iOS8 it should appear here.

Since iOS8 you can get the focus value from the lense by key-value observing lensPosition. It is a property of the AVCaptureDevice class which is part of the AVFoundation framework.

So somewhere in your camera class set the observer:

// Assuming _device is an object of the `AVCaptureDevice` class
[_device addObserver:self forKeyPath:@"lensPosition" options:NSKeyValueObservingOptionNew context:nil];

And in the class you used as observer:

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    if ([keyPath isEqualToString:@"lensPosition"]) {
        NSLog(@"change: %@", change);
        NSLog(@"lens position: %f", [change[@"new"] floatValue]);
    }
}

The position of the lens will be displayed as a scalar value from 0 to 1. Also you can set the lens position manually. You can find out more about managing the lens position in the Apple Documentation.

Finally as with all key-value observer don't forget to remove the observer.

NOTE: The lens is a mechanical part in the device and focusing is done by moving the lens via a spring. So values differ depending on the device and situation.

Answer 2

I do not think there is such a thing as a focus value.