iPhone 6 Plus Optical Image Stabilization (OIS) Explained

September 30, 2014

iPhone 6 Plus optical image stabilization explained in depth

In this article I want to talk about the benefits of the iPhone 6 Plus OIS. OIS is short for Optical Image Stabilization.  The OIS is a mechanism in the camera lens which is designed to counter several issues in photography. Understanding what the purpose of the OIS is, will help you understand what it such an important feature in the iPhone 6 Plus and what you want to have it.

Some people will probably buy the iPhone 6 Plus for its optical image stabilization, although before you are making this choice, you should understand its benefits.

The OIS on the iPhoen 6 Plus works by moving the lens part from side to side to compensate for hand movement. So what is it important? — well, when you hold the phone in your hand to snap a photo, your hands moves slightly to different direction as your are and hand muscle work to hold the phone steady. Those tiny movements are the ones that responsible to blur in photos and shakiness in videos.

When taking a photo in good lighting condition and in auto mode, it’s almost unlikely that you’ll see blur in photos. The main reason for that is that the camera is choosing a shutter speed that allows it to achieve a sharp image and get the correct exposure right. The shutter speed is like a window that opens up to let light pass through to the sensor for a given amount of time. It is measures in second. For example 1/500 sec, which equals to 0.002 seconds or 2 milliseconds. This is a very fast shutter speed,

According to the shutter speed rule of thumb, in order to get a sharp image, you should be capturing a photo at a minimum shutter speed equals to 1 divided by the equivalent focal length of the lens. So for example, we know that the iPhone 6 Plus lens focal length (of the main camera) is equivalent to 29mm. This means that in order to get an acceptable sharp photo, we should be shooting at a minimum shutter speed of 1/29 seconds, which is approximately 34.5 milliseconds.

If you decide to shoot at lets say 1/500 sec (2 milliseconds), you are in a very high likelihood to get sharp photo, because 1/500 sec is 17.25 times faster than 1/29 sec.

The camera does the inner calculations in order to make sure that you get a sharp image. By saying “inner calculations”, it means that the camera, if set to auto mode, automatically sets the ISO , shutter speed and aperture. The Aperture is the hole from which the light passes through the lens. The larger the whole, the higher the amount of light. Aperture is signified using f-numbers. For example, the iPhone 6 Plus has a maximum aperture of f/2.2 (can be written also as F2.2). The maximum aperture is the largest possible size of that hole which the light passes though. The larger that hole/pupil, the smaller the f-number. So for example, f/5.6 means that the pupil of the lens is smaller, and less light can pass through.

So what all this has to do with the iPhone 6 Plus IOS you ask. Well, when you shoot in low-light situations, the camera needs to allow more light to pass through or to amplify the light values captured by the sensor  in order to get the correct exposure to lighten up the scene. In low-light, like the words describe, there is less light. Without light you won’t be able to see anything in the photo (or video). So in order to compensate for the lack of light, the camera can do one of those things:

  1. Reduce the shutter speed to allow more light to reach the sensor
  2. Open up the entrance pupil (think of it like the pupil of the human eye) to let more light come in
  3. Increase the ISO of the sensor, which amplify the light values
  4. Turn the flash on to provide illumination to the scene

One problem when shooting in low-light is when the camera is exhausting the aperture and shutter speed options and move to the ISO in order to get a good exposure. The iPhone 6 Plus camera can open the aperture as large as it can (aka “Maximum aperture”) and shoot at a slower shutter speed recommended to get a sharp image, but if there is still not enough light, the camera uses higher ISO speeds.

The use of higher ISO settings causes more digital noise due to amplifying the signals on the sensor, thus lettings the sensor read some weaker signals. The problem is that the sensor also gets the background electrical noise amplifying the of light photons. I won’t get into that in-depth, but the larger the pixels, the better the Signal-to-noise ratio.

So when the camera uses a higher ISO sensitivity, we get to see more noise in our images, which is obviously less pleasant to view than a sharp and clean image. If in Auto mode, the camera had decided to use a slower shutter speed instead of using higher ISO setting, it would be shooting at shutter speed slower than the recommended one for a sharp photo, and the hand movement of the photographer and the movement of the device, would have lead to a blurry picture.

This is one reason why people that shoot in low light and in low ISO get a blurry image or a dark image if the shutter speed stayed in the recommended zone and the ISO stayed the same. When shooting in manual mode (possible via certain iOS app and now available in iPhone 6 and iPhone 6 Plus), you have the option to control the shutter speed, aperture and ISO.

The Optical image stabilization (OIS) was designed in a way that it moves the lens to compensate for those small hand movement that leads to blurry images when shooting at slow shutter speeds. If you shoot at the recommended shutter speed according to the shutter speed rule of thumb, the OIS won’t show its advantage (when shooting stills). It’s only when you decide to lower the shutter speed below the recommended one, that you’ll notice a difference.  For videos it’s more prominent because the camera continuously recording images at very high frame rate (30 fps or 60 fps). I personally don’t know how fast the compensation works (how many corrections per second), but it should significantly improve shakiness when recording videos.

In order to improve the video stabilization, Apple also used a digital image stabilization called “Cinematic Video Stabilization”. This digital stabilization id done via software to further correct tiny movements and optimize the viewing experience.

Check out this comparison video made by a YouTube user that shows that the OIS makes videos more stabilized on the iPhone 6 Plus compared to the iPhone 6 that lacks OIS.

Another iPhone 6 vs iPhone 6 Plus camera test comparison video, this one made by SuperSaf TV

Now with the optical image stabilization, the knows that it can use slower shutter speeds instead of using higher ISO settings. How much slower? — it depends on the OIS effectiveness. The compensation is usually measured in stops or some called  “steps”. A 3 stops compensation means that you can shoot with a shutter speed 3 stops slower to get the same sharpness.

To keep things clearer, lets take a look at the iPhone 6 Plus lens specs for a second.

We know that the lens is equivalent to 29mm. This means that in order to get a sharp image I need to shoot at a minimum shutter speed (slowest shutter speed) of 1/29 seconds. Shooting slower than that, I risk getting a blurry image.  I assume that the iPhone 6 Plus OIS is effective up to 2 to 3 stops more or less. I don’t know the exact number and I didn’t have the change to check it myself.

If it’s lets say 2 stops. This means that we can shoot at 1/8 seconds (1/30 -> 1/15 -> 1/8). Each shutter speed stop is two times slower or faster than the stop above or below it in the shutter speed stop’s scale. One stop equals to two times the amount of light. Shooting at 1/8 sec means that the camera allows four times the amount of light to pass through the lens compared to 1/29 sec (I rounded up to 1/30). So instead of shooting at ISO 400 and have a noisy image (in some degree), I can shoot at ISO 100 for that same exposure and get a clean image with much less or no noise at all (depends on the sensor performance).

Furthermore, ins some very dark lighting conditions, you’ll be able get e good exposure, that with the iPhone 6 you’ll be getting a dark image. This is because at very dark situation, the camera might already be using the highest ISO, maximum aperture and slowest shutter speed – but even than it’s not enough to get a good amount of light to get a well exposed image. So with the iPhone 6 Plus you’ll be able to shoot at even darker scenes and still get a well-exposed image, or at least one that is much better than what you get with the iPhone 6 without an Optical Image Stabilization (OIS) in both manual or auto mode.

So the iPhone 6 optical image stabilization (OIS) can really help in low-light and when shooting videos.

Check out the iPhone 6 Plus vs iPhone 6 size comparison here to see if the size of the iPhone 6 Plus might be too big for your taste, regardless having a built-in optical image stabilization.

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