In almost all Android devices, zoom is digital -- there just isn't a mechanism for changing the length of the barrel and gathering more info.

So how is focus achieved?

If you're not physically changing the lens properties, or extending the barrel length, you've only got dilation of the aperture as the last focus method. Which is mechanical. Unless you've got a fixed focus system -- which most android phones do not seem to have.

The android-spec for the autoFocus() method isn't much help - although it says it must be supported by the hardware, although most phones seem to have it.

So if it is hardware -- how? I'm not hearing any little motors whirring around in there.... And is there really even any room for a mechanism in these things?

See Also:

  • 1
    Sorry I know this question is almost 10 years old but I can't find many relevant discussions regarding this topic. Your link says that camera apps almost always use digital zoom, but the answer you selected says there is a mechanical zoom, which you seem to agree with based on your comment. I still find this very hard to believe that a mechanical zoom would be present inside a phone case. Was that for a specific device? Or do phones actually come with mechanical zoom?
    – user17915
    Aug 5, 2019 at 9:13
  • The phone I had at the time I claimed to hear the auto-focus is long gone. Based on some other reading - photo.stackexchange.com/questions/31227/… - it appears that some phones have a mechanically controlled APERTURE. androidcentral.com/understanding-aperture-and-why-it-matters Oct 8, 2019 at 16:07
  • Ah, here's some more that claims that most phones TODAY have mechanical focus on the rear-facing camera: giffgaff.com/blog/how-does-auto-focus-work-on-your-smartphone Oct 8, 2019 at 16:08

2 Answers 2


The focus function is achieved by moving the lens back or forth so it is actually a mechanical thing.

You can try it yourself. Download ZXings Barcode Scanner and fire it up. You'll hear a click every time it tries to refocus you can also see the lens moving back and forth.

  • Loooong delay prior to accept. I just didn't hear the auto-focus sound until recently. Nov 26, 2010 at 12:32

Often there is no focus at all. These cameras often make up for a complete lack of focus by having a large depth of field, which is exactly what is done with those "disposable" film cameras.

Digital zoom is a simple scaling of the input image, so there's no need to adjust zoom when digital zoom is applied, for the same reason there's no need to apply focus when scaling an image in photoshop. Focus is only needed for optical zooms because optical zoom changes the focal length of the camera.

  • My Incredible has digital zom, but it also has (Auto) focus. I know it's not wide depth of field, because whatever is out-of-focus is variable. Nov 8, 2010 at 12:05
  • Digital zom? Does your Android have digital zom? nope! Nov 26, 2010 at 12:33
  • @Michael: I can't afford an Android, so I have absolutely no idea. You'll notice that nothing in my answer is inherently android specific -- I'm just generalizing from cell phone cameras I've seen that don't actually have hardware (optical) zooms. If your camera has optical zoom, then it would need some kind of focus. Otherwise there's no reason it couldn't get away with the high depth-of-field trick used in the "instamatic" cameras which don't have focus hardware at all. This is why I used the word "often" above -- I don't have specific hardware to play with. Nov 26, 2010 at 19:03
  • And what I said about digital zooms is true -- there's no change in focus required on a digital zoom. I have no idea whether or not android as a system uses digital zoom or not. Nov 26, 2010 at 19:04
  • Sorry, I was riffing on my mis-spelling; Most androids [as of late 2010] do have auto-focus instead of fixed focus, so I went w/ @Octavian's answer Nov 26, 2010 at 20:06

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