Photography instructors often teach that a wide aperture (like f/2.8 or f/1.8) creates shallow depth of field—those dreamy blurred backgrounds. That’s true… but it’s only part of the story. And for many photographers, especially those using Micro Four Thirds or phones, it can lead to confusion.
Let’s break it down.
What Really Controls Depth of Field?
Depth of field (DoF) is influenced by four key factors:
1. Aperture (f-number) – Wider = shallower DoF. Narrower = deeper DoF.
2. Focal Length – Longer lenses isolate subjects more (e.g., 85mm vs. 25mm).
3. Distance to Subject – Closer focus means shallower DoF.
4. Sensor Size – Bigger sensors give shallower DoF at the same framing and aperture.
Why It Matters
If you're using a phone with a fast f/1.5 lens, you might wonder:
> “Why isn’t my background blurry?”
It’s because your phone’s sensor is tiny, and its lens is ultra-wide. Even at f/1.5, almost everything stays in focus due to optical physics.
If you're using a Micro Four Thirds camera, you might notice that f/2.8 doesn’t blur backgrounds as much as a full-frame camera. That’s because your sensor is smaller—so you get more depth of field at a given aperture and framing.
What Instructors Should Say
Instead of just “use a wide aperture,” instructors should teach:
> “To control depth of field, consider aperture, focal length, distance, and sensor size together. A wide aperture helps—but only in context.”
That’s real instruction.
A Practical Example
Phone camera: 4mm f/1.5 lens = almost everything in focus
MFT camera: 25mm f/1.8 lens = some blur, more control
Full-frame: 85mm f/1.8 lens = rich background blur, even at a distance
Same f-number, totally different results.
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Bottom line: You deserve instructors who explain, not just prescribe. Photography is part science and part art—but learning works best when we teach the science clearly.
