What is the focal length of an iPhone Camera and Why Should I Care?

In order to get the most out of your smart phone camera, whatever the brand, there are a few things you should know, one of which is the focal length of the lens you’ll be using.  Sure, you could leave everything on auto and snap happily away, but you’ll be disappointed with some of your images because you aren’t playing to the camera lens’ strengths or just might be inadvertently accentuating the camera lens’ weaknesses. 

Although this article focuses on iPhones, many Android phones, as well as Google’s Pixel phones, have similarly terrific camera systems.  These little devices can be stupendous when used smartly.  You’ve probably seen the Apple ads about movies and billboards shot on an iPhone.  Yes, you can do that, but only if you really know the capabilities of your device.

What are the focal lengths and how do they compare with a regular camera?

So, let’s start with the lens.  In a typical full-frame DSLR, you’ll might have a prime lens that has focal length of, for example, 50 mm.  That’s roughly the field of view we see with our eyes.  Crop sensor cameras have smaller sensors and smaller lenses.  A lens with a focal length 35 mm on many crop sensor cameras has the equivalent field of view of a 50mm lens on a full-frame camera. 

Telephoto lenses on a full frame camera are generally 70 mm or longer.  On a crop-sensor camera, that would be about 45 mm or longer.

Wide angle lenses on a full frame camera are generally 28 mm or shorter.  On a crop-sensor camera, that would be about 18 mm or shorter.

So, how does an iPhone Xs or Xs Max stack up?  The wide-angle lens on an iPhone Xs or Xs Max has a focal length of 4.25 mm, which is equivalent to 26 mm on a full-frame camera.  That’s wider than the 28 mm equivalent in the iPhone 7+, 8+ and X models, and wider still than earlier models’ 33 mm equivalent.  The telephoto lens is 6 mm, which is equivalent to a 52 mm lens on a full-frame camera.  (Earlier iPhones, including the 7, 8, and the Xr only have one front-facing camera and lens.) In addition, the iPhone has a rear-facing camera, often used for selfies, that Apple now calls the TrueDepth camera.  It has a focal length of 2.87 mm but neither Apple nor third-party reviews list the full-frame equivalent for this lens.

Why focal length matters

Field of View:  If you’re mostly using the wide-angle lens, your iPhone will have a very wide field of view.  You’ll be able to get a lot of the landscape or cityscape in your photo.  As with any wide-angle lens, foreground elements will become more prominent and distant elements will appear smaller.  That rock in the foreground of your landscape photo will look bigger and the distant mountain appears smaller.  If you’re taking a close-up portrait of someone, their nose might appear more prominent as it’s closer to the lens.

When you switch to the telephoto lens on your iPhone, you’re getting some magnification, but not a ton.  Those distant mountains will appear closer and larger and the landscape will seem a bit more compressed, but not a lot. 

You can use your fingers to digitally zoom in on either the wide-angle or telephoto lens to refine your composition.  With the telephoto lens, you can digitally zoom in up to 10 times.  Unlike a true zoom lens, however, you are not really zooming in.  Instead, you are using a smaller and smaller area of the camera’s sensor to make the subject appear larger. 

By zooming in, you are trading magnification for resolution.  Try this experiment.  Use your phone to photograph something with a pattern or texture.  Shoot the first shot with the telephoto at its normal setting.  Then zoom in all the way to 10x and take a second shot  Compare the amount of detail and sharpness between the two shots and you should see a noticeable difference. 

One thing to note:  You switch to the telephoto lens by tapping the circle with “1x” inside.  It activates the telephoto and changes to display “2x” inside the circle.    Sebastian de With (on Twitter @sdw) reported that, if you take a photo with ‘2x' enabled, and the image focus point is closer than the telephoto lens' minimum focal distance (which is about 12 inches) the camera will just grab the image from the wide-angle lens and upscale it by using a smaller area of the sensor, as described above.

Sharpness and image stabilization:  Ideally, you’ll brace your phone against something stable as you shoot, but that’s not always possible.  Holding your iPhone as you snap a photo can reduce sharpness a bit as your hand will be moving, however slightly.  A telephoto lens magnifies that movement.  That’s why there’s a “rule” for hand held shots with a full frame camera stating that you shutter speed should be equal to or faster than 1/focal length of the lens—50 mm and 1/50^th sec., 200 mm and 1/200^th sec.  If you have your iPhone zoomed in 10x, you will get more fuzziness from the motion of your hands than you wood at 2x.  The Xs and Xs Max (along with the 7+, 8+ and X) have optical image stabilization built in, which will mitigate most of your hands’ movement.

Depth of field:  Depth of field is the distance between the nearest and farthest elements in a scene that are in acceptably sharp focus. (If you want to learn more about depth of field, see this article and this article.) 

The available depth of field increases as the sensor size and lens focal length decrease.  (That’s simplifying a lot of variables, but accurate for the purposes of the point I want to make here.)  So, a crop-sensor camera with a 35 mm lens will have a greater depth of field than a full-frame with a 50 mm lens because, although the field of view is the same, the sensor is smaller.  A 15 mm lens will have a greater available depth of field than a 24 mm lens on the same camera because it has a shorter focal length.

According to dpreview.com, the iPhone Xs and Xs Max have dual 12 MP sensors made by Sony for the front-facing cameras.  Each sensor measures 7.01 x 5.79 mm, with an active area that’s 5.6 x 4.2 mm, about the same size as a 1 x 2.5” sensor.  Compare that to a full-frame sensor, at 36 x 24 mm or a crop sensor at 23.6 x 15.7 mm.  The much smaller iPhone sensor (about 35 times smaller in area than a full frame camera) and very short lenses mean the camera has a truly massive depth of field when you’re shooting landscapes and many day-to-day shots.  Even focusing on something close by isn’t enough to throw the background out of focus enough to create a pleasing bokeh.  To do that, the iPhone engineers created Portrait Mode, where the software combines photos taken by both the wide angle and telephoto lens, does some computational magic, and creates a creamy, blurred background.

Apple also has a new Depth Control feature that allows you to adjust the depth of field and, thus, the bokeh as you are composing your shot or even after you’ve taken the shot.  You do that by manipulating the camera’s aperture, which can be as wide open as f1.8 on the wide-angle lens or f2.4 on the telephoto all the way down to f16.

ISO and image quality:  The experts at Halide report that the new sensor on the iPhone Xs and XS Max sports an expanded ISO range.  On the wide-angle lens, ISO now goes from ISO 24 to ISO 2304, which results in more sensitivity and less noise in low light situations.

For the Telephoto lens, the maximum ISO goes from ISO 1200 to ISO 1440, again resulting in more sensitivity and less noise in low light situations.

Also of note:  Halide states that the Xs and Xs Max are now able to take an exposure of up to a full second, enabling some interesting long-exposure effects.  Previous models topped out at one-third of a second.  The ISO range has also been expanded, allowing captures with a little less noise.  The wide-angle lens sensor goes from ISO 24 to ISO 2304 and the telephoto goes up to ISO 1440, both increasing about 200 from previous models.

Recording video:  As many of us capture video on our phones, it’s worth a few moments to look at the interplay between quality video and focal length.  iPhones can record 4K video.  You can even pull 8MP still frames from 4K video.

You can use either the forward-facing telephoto or wide angle lens for shooting video.  Both have optical image stabilization for video.  While you can get 2x optical magnification using the telephoto lens, you can only digitally zoom to 6x (unlike the 10x of still photos).  And, remember, it gets to 6x by using a smaller area of the sensor, rather than truly zooming the lens beyond 2x.

With more and more people taking photos (and videos) on smart phones, and with those smart phone cameras getting better and better, amateur photographers are filling Instagram and YouTube with some outstanding images (and a lot of dreck).  The cameras and sensors in these small packages are so capable that even professional photographers are using the phone in their pocket to capture stunning, portfolio-quality images.  The best know what they’re doing and know every facet of their gear.  The photos and videos they capture play to the strengths of the cameras and lenses, while minimizing the weakness of their gear.  Now you can, too.

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