iPhone Life magazine

Rules of iPhoneography: Depth of Field

Sharp focus is one of the key aspects of capturing a great photograph. Focus and exposure are probably the two most critical technical areas photographers need to understand, and my last post, "Rules of iPhoneography: Capture Every Detail with These Exposure Tricks," looked at exposure in some detail. For my second post, I want to focus on focus (really sorry, couldn't help myself).

The iPhone, like all phone camera technology I'm aware of, gives us very little scope to play with focus at the point of capture. This is because the relationship between its optics and its sensor is such that typically the vast majority of the scene will be in focus, or almost in focus, even if we just point and click. We would describe this as a large depth of field or depth of focus.

'Depth of field' refers to the range of distance that appears acceptably sharp.

Really, an image is either in focus or out of focus when captured. It is possible to play around with sharpening and clarity processes to get the best out of a slightly out of focus shot, but what is captured is captured. This article therefore looks in more detail at depth of field as applied to iPhoneography.

 

Mentioned Apps:

 

Key Apps:

 

Focus/Depth of Field Options

 

1. At the point of capture

At the point of capture we can use the iPhone as a simple point and click and allow the auto-focus to take care of the scene. For many typical scenes this will be more than adequate. Alternatively, we can manually set the focal point by dragging the square box in ProCamera (or equivalent in other apps) over the subject of interest. This will ensure the sharpest focus. Once the box stops blinking the focal point is locked.

Setting the focal point manually is not only best practice but it is absolutely essential when capturing images close to the iPhone. This is because at close range the 'depth of field' becomes shallow and as such only a small proportion of the image will be focused. It should be noted whilst the focal point can be controlled, there is no way to control 'depth of field' at capture on iPhone. The 'depth of field' is controlled in traditional camera technology by the aperture and in the case of iPhone5 this is fixed at F2.4. These 2 images of a tape measure highlight this point:

This example uses ProCamera (left to right):

  • Image One: Screen shot shows the blue square focus point between 1" and 2".
  • Image Two: The resulting image shows a very narrow 'depth of field' with roughly the area between 2" and 3" in focus.
  • Image Three: Screen shot shows the blue square focus point between 7" and 8".
  • Image Four: The resulting image shows how the area of focus has changed from image two. It is also worth noting that as we focused further away the 'depth of field' increased.

This is all very nice for Macro style shots. Getting close to small objects it is possible to make them stand out from the background using focus alone. No post processing required here. The challenge comes when we have a more typical scene and we want to really draw attention to a subject. A photographer using a typical camera would possibly set the camera up to achieve a shallow 'depth of field' via the aperture. Blurring the foreground and background and drawing the subject sharply in to focus. iPhoneographers don't have that option. For us, we have to set about simulating the effect using apps in post processing.

 

2. Post processing to simulate shallow depth of field

The iPhoneography image at the head of this article is a reasonably typical night scene. Very often photographers like to work with a wide aperture at night for 2 main reasons:

  • Unless a long exposure shot is planned a wide aperture lets in more light and therefore reduces shutter speed reducing motion blur.
  • A wide aperture gives a shallow 'depth of field' helping the subject stand out but also generating some amazing 'bokeh'.

'Bokeh' has multiple definitions but for the purposes of this article I'm using it to refer to how out of focus specs of light are distorted to create a beautiful background 'canvas'.

The following images show how the shallow 'depth of field' and bokeh transformed an initially promising capture into an image with beautiful 'bokeh':

(left to right)

  • Image One: Captured on 6x6 app on iPhone4 through a bar window at roughly midnight. The image is noisy due to the low light levels but it can be seen that almost the entire scene is in focus (although there is some blur due to the shutter speed).
  • Image Two: The image was cropped and resized (Filterstorm).
  • Image Three: The magic app to generate 'depth of field' is AfterFocus. As an alternative an app called Big Lens can also be used. The focal area is manually masked and then blur levels, aperture shapes and 'bokeh' turned on. The result is that the masked foreground remains focused but other background areas become blurred. Additionally, the light points generate the traditional circular out of focus 'bokeh'.

It is this 'bokeh' that sets apps like AfterFocus and Big Lens apart from apps that simply blur an image. 'Bokeh' gives a much more realistic out of focus effect. We therefore create an illusion of 'depth of field'.

An additional filter was also applied via 100CamerasIn1 to further enhance the image.

 

Other focus techniques

Traditional photography provides the ability to distort the focal plane resulting in some great effects. Images generated by lens-baby, tilt and shift processes (known as tilt-shift but separate techniques) and freelensing can all be simulated in iPhoneography post processing. I'll leave that for a future article.

Thank you very much for reading and I hope it proves useful.

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Paul Brown (known to all as Skip) is an exhibited and prizewinning iPhoneographer from Lincoln, England. He is a member of the global Advanced Mobile Photography Team, a managing member of Lincolnshire-based regional mobile photography Group InstaChimps, and a founding artist at New Era Museum. Skip was a finalist in the Photobox Motographer of the Year 2012 with his image ‘Skipping’ and also has a personal iPhoneography blog at skipology.com.