The Truth about Sensor Size

Life is full of foolish myths, ideas that get planted into our brains by rumor or gossip or misperception, and seem to endure.

One of those myths in photography is that sensor size affects depth of field. I hear it all the time in class, in the field, and, of course, on the internet.

The widely held notion is that larger imaging sensors create shallower depth-of-field, and that’s simply not the truth.

Take a look at this example.

Cameras and Christmas lights.
Cameras and Christmas lights.
Christmas lights and cameras.
Christmas lights and cameras.

Okay, here is the real truth: these images are identical… same focal length, same aperture, same shutter speed, same ISO, same lighting, same distance from camera to subject. Literally the only difference is the sensor size. Look all your want, and then try to guess which one is 36x24mm sensor, and which is made with a 24x16mm sensor.

But how can these images be identical? Doesn’t everyone, everywhere know that larger sensors create shallower depth of field? Shouldn’t I “upgrade” to a bigger sensor to get shallower depth of field?

No. What’s really happening is that when you switch from a smaller sensor to a larger one, in order to create the same composition, you either have to move closer, which creates shallower depth of field, or you have to use a longer focal length, which creates shallower depth of field.

I know I’m not going to change the world’s mind about this, since it is so ingrained in the psyche of photography, but maybe at least a few curious, budding photographers out there will figure it out.

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