The iPhone’s Portrait mode uses computational photography to simulate the shallow depth of field of a digital SLR or mirrorless camera with a larger sensor. It’s evolved from a very crude tool into something which is now pretty convincing, but it’s still no substitute for the real thing.
There are some circumstances in which you can get genuine shallow-ish depth of field with an iPhone shot, but these are very limited as we’ll discuss. The Sandmarc 2x telephoto lens is a much more practical way to get true optical blurring when shooting portraits …
Your quick primer on depth of field
Depth of field is a way of describing how much of your photo is in focus. Sometimes we might want the entire photo in focus, while other times we might want a wafer-thin focal plane. Let’s use a couple of digital SLR shots to illustrate.
In this first case, I wanted everything in focus from the leaves of the tree just a few feet in front of me right the way through to the opera house and bridge around half a mile away. I therefore used a narrow aperture of f/16 to create a very deep focal plane. This is pretty similar to the default depth of field you’ll get from an iPhone.
Contrast with this shot where I’ve shot at f/1.4 so that only the closest eye is fully in focus and even her hand, just a foot or so behind, is completely blurred. This is something completely impossible on an iPhone.
Achieving a depth of field this shallow was only possible because I was shooting on a full-frame camera with a very fast (wide aperture) lens.
The limitations of Portrait mode
What Portrait mode on the iPhone does is to simulate shallow depth of field by computationally figuring out what is in the foreground and then artificially blurring the background. In recent years, it even simulates a gradual fall-off of focus as things get progressively further away from the camera.
I’ve grown increasingly impressed with this over the years, especially since it started supporting night shots too. However, it’s far from perfect, sometimes delivering what looks like a green-screen cutout effect.
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