Why does a larger sensor seem to give shallower depth of field?
Asked 5/16/2011
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I often read that full-frame cameras give shallower depth of field than APS-C. I understand the field-of-view difference, but not why sensor size would affect depth of field.
If two cameras use the same lens and f-number, does the larger sensor itself reduce depth of field? Or is the effect only seen when you change focal length or camera distance to keep the same framing/composition?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
15y ago
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Firstly, the number of wells on the sensor has no bearing on where you can focus or 'how much' you can focus on. Out of focus light is still light hitting the sensor.
Simply put, you have shallower depth of field with a full-frame sensor because you have to get closer to the subject (or zoom in) in order to fill the frame. Note that in your example it says same composition: the camera has been moved or the focal length changed in order to fill the frame with the bottle.
To put it another way, if you fix a tripod in place and take a shot with an APS-C camera with the bottle filling the frame, then take the same shot in exactly the same position with a full-frame camera, you will have more space around the bottle. So you will either need to zoom in or move the camera closer to achieve the same shot where the bottle fills the frame, either of which will alter the depth of field,
See this excellent summary of sensor sizes and their effects.
Originally by user3205. Source · Licensed CC BY-SA 4.0
user3205
15y ago
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A larger sensor does not inherently change depth of field by itself. If you keep the same lens, aperture, and camera position, the optical depth of field is the same; the larger sensor just captures a wider field of view.
The “full frame has shallower DoF” effect appears when you try to match framing/composition between formats. To make a subject the same size in the frame on a larger sensor, you typically either:
- use a longer focal length, or
- move closer.
Both of those changes reduce depth of field.
Another way to see it: depth of field is tied to the physical aperture size as well as magnification. At the same f-number, a longer focal length has a larger physical aperture diameter, which gives shallower depth of field. So if full frame uses a longer lens to match an APS-C composition, it will blur the background more.
So the sensor is not directly causing shallower depth of field; the change comes from the lens focal length or shooting distance you choose to get the same picture.
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