Sensor Size April 20, 2026 4 min read

Full Frame vs Crop Sensor: The Real DOF Differences

"Full frame gives shallower depth of field" is one of the most repeated claims in photography, and it is true under one set of conditions. Change the comparison and the answer changes. Here is what sensor size does to depth of field and what it doesn't.

Crop factor

The crop factor is the ratio of a full-frame sensor's diagonal to the smaller sensor's diagonal. A 1.5x sensor sees the same field of view with a lens 1.5 times shorter than full frame needs, so a 50 mm lens on APS-C frames like a 75 mm on full frame.

Format	Crop factor	Sensor size	Lens that frames like a 50 mm on full frame
Full frame	1x	36 x 24 mm	50 mm
APS-C (Canon)	1.6x	22.3 x 14.9 mm	31 mm
APS-C (Nikon, Sony, Fuji)	1.5x	23.5 x 15.6 mm	33 mm
Micro Four Thirds	2x	17.3 x 13 mm	25 mm
1-inch	2.7x	13.2 x 8.8 mm	18 mm

Same lens, same distance, same f-number

Put a 50 mm lens at f/2.8 on full frame and on APS-C, stand 3 m from the subject, and shoot both. The optics are identical, and the APS-C picture is simply a crop of what the full-frame one captures. But when you view the two full pictures at the same size, the APS-C one has been enlarged more, so the same blur looks bigger, and it counts as shallower: about 37 cm against 58 cm. Similarly an 85 mm f/1.8 at 2.5 m gives a zone of 5.7 cm on APS-C and 8.7 cm on full frame. This is a surprising result for anyone who thinks full frame is always shallower, and it is rarely what people mean by the comparison. They mean the same shot, composed the same way.

Same framing, same f-number

That is the fair comparison. To frame a head-and-shoulders portrait on APS-C like an 85 mm shot from 2.5 m on full frame, you use a 56 mm lens from the same spot. At f/1.8 on both, the full-frame zone is about 8.7 cm deep and the APS-C zone about 12.9 cm. The ratio, about 1.5, is the crop factor. In stops of f-number, that is about 1.2 stops for APS-C, 2 stops for Micro Four Thirds and roughly 3 stops for a 1-inch sensor. The reason is that depth of field is proportional to the f-number times the circle of confusion times the distance squared, divided by the focal length squared. The shorter lens on the smaller sensor adds more than the stricter circle of confusion takes back, and the net effect is the crop factor. The circle of confusion post shows the arithmetic.

Matching the depth of field

You can close the gap with a wider aperture on the smaller sensor: divide the f-number by the crop factor. The APS-C 56 mm at f/1.2 gives 8.6 cm in the example above, matching the full-frame 85 mm at f/1.8. Equivalents work out like this:

Full frame	APS-C (1.5x)	Micro Four Thirds (2x)
85 mm f/1.8	56 mm f/1.2	42 mm f/0.9
50 mm f/1.4	33 mm f/0.93	25 mm f/0.7
135 mm f/2	90 mm f/1.33	67 mm f/1.0
85 mm f/1.4	56 mm f/0.93	42 mm f/0.7

Some of those lenses exist, such as the 56 mm f/1.2 on Fujifilm APS-C and 42.5 mm f/0.95 lenses for Micro Four Thirds, but others are not available. So matching full-frame blur on a smaller sensor gets harder the faster the full-frame lens is. Equivalent aperture changes depth of field, not exposure, since exposure depends on the actual f-number. And true equivalence also scales ISO: full frame f/1.8 at ISO 1600 corresponds to APS-C f/1.2 at about ISO 700, which is why equivalent pictures show about the same noise.

Where it matters

For portraits, fashion and anything where thin focus is the point, the full-frame advantage is real, and f/1.2 and faster on full frame has no equivalent on smaller sensors. For landscapes and architecture, the deeper focus of a smaller sensor is an advantage: Micro Four Thirds at f/5.6 matches full frame at f/11 for depth, though diffraction arrives earlier on its smaller pixels, as the diffraction guide shows. For macro, smaller sensors need fewer frames to stack. For wildlife, the extra reach of APS-C often matters more than a stop of depth of field.

Blur quality is separate

How the out-of-focus areas look depends on the lens design, aperture blades and aberrations, not directly on sensor size. See the post on aperture blades and bokeh shape.

Sensor	Depth of field vs full frame (same framing and f-number)
Full frame	Reference
APS-C (1.5x)	about 1.5 times deeper, around 1.2 stops
Micro Four Thirds (2x)	about 2 times deeper, 2 stops
1-inch (2.7x)	about 2.7 times deeper, around 3 stops

Sensor size is one input to depth of field, not the only one, and it is rarely the deciding factor in choosing a camera. Compare it against size, weight, cost, lens choice, noise and reach. To see the numbers for your own setup, use the calculator.