explainer
How to Blur the Background: The 4 Keys to Depth of Field
By the LazyTools team · Published 2026-07-12 · Updated 2026-07-12 · 3 min read
That gorgeous blurred background — the one that makes a subject pop — is a shallow depth of field, and it’s controlled by just four things. Master them and you can dial in exactly how much of a photo is sharp: a paper-thin slice for a dreamy portrait, or everything from the flowers at your feet to the distant peaks.
1. Aperture — the big one
The aperture is the adjustable opening in the lens, measured in f-numbers. It’s the most direct control: a wide aperture (a low f-number like f/1.8) gives a shallow depth of field and a soft background; a small aperture (a high f-number like f/16) keeps far more in focus. Confusingly, smaller f-numbers mean bigger openings — f/1.8 is a wide aperture, f/16 is a narrow one. Start here: to blur a background, open up.
2. Focal length — longer blurs more
For the same aperture and subject size in the frame, a longer lens gives a shallower depth of field. An 85mm portrait lens throws a background far more out of focus than a 24mm wide-angle at the same f-stop. It’s a big reason portrait photographers reach for 50mm, 85mm and 135mm lenses.
3. Subject distance — get close
The closer you focus, the shallower the depth of field. Move in tight on your subject and the background dissolves; back away and more comes into focus. This is why macro photos have razor-thin focus — at a few centimetres, the depth of field can be millimetres. It also means distance between the subject and the background matters: the farther the background, the blurrier it renders.
4. Sensor size — bigger blurs more
For the same framing, a larger sensor gives a shallower depth of field. A full-frame camera blurs backgrounds far more easily than a phone, because to get the same field of view a phone uses a very short lens — and short lenses have enormous depth of field. That’s the whole reason your phone fakes the blur with a software “portrait mode” instead of doing it optically. The crop factor calculator shows the equivalent aperture across formats.
The two recipes
Put the four together and you get a simple recipe for either extreme:
- For a blurry background: wide aperture (low f-number) · long lens · get close · big sensor · lots of distance to the background.
- For everything sharp (landscapes): small aperture (f/8–f/16) · wide lens · step back · and focus at the hyperfocal distance rather than the horizon, to squeeze out the maximum front-to-back sharpness.
Want the exact numbers for your gear? The depth of field calculator gives the near and far limits for any sensor, lens and aperture, and the hyperfocal distance calculator finds the perfect landscape focus point — all worked out privately in your browser.
Depth-of-field figures use the standard optics equations with the circle of confusion set to the sensor diagonal ÷ 1500, and verified sensor dimensions. Results match established DoF calculators; treat “acceptably sharp” as a guideline that depends on print size and viewing distance.
Frequently asked questions
What is depth of field?
The range of distances in a photo that look acceptably sharp. A shallow depth of field has only a thin slice in focus (blurry background); a deep one keeps everything sharp from foreground to horizon.
How do I blur the background of a photo?
Use a wide aperture (a low f-number like f/1.8), a longer lens, and get close to your subject — and put distance between the subject and the background. A larger sensor helps too. All of these shrink the depth of field.
What aperture gives a blurry background?
A wide one — f/1.4, f/1.8 or f/2.8 give a noticeably shallow depth of field and soft background. The higher the f-number, the more comes into focus, so f/8–f/16 keeps backgrounds sharp.
Does focal length affect depth of field?
Yes — for the same aperture and framing distance, a longer lens (say 85mm) gives a shallower depth of field and more background blur than a wide lens (24mm). It's why portrait lenses are longer.
Why does my phone struggle to blur backgrounds?
Because its sensor is tiny. Small sensors use very short lenses to get their field of view, and short lenses have a lot of depth of field — so everything tends to look sharp. Phones fake the blur with software 'portrait mode.'
How do I get everything in focus for a landscape?
Use a small aperture (f/8–f/16), a wide lens, and focus at the hyperfocal distance rather than the horizon. That maximises the depth of field so foreground and background are both sharp.
What is bokeh?
The aesthetic quality of the out-of-focus blur — the soft rendering of background highlights into smooth circles. It comes with a shallow depth of field, and its look depends on the lens's aperture design.