How does using a full-frame lens on a smaller-sensor camera affect field of view and depth of field?

Asked 5/16/2011

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I mounted a Nikon 50mm f/1.4 lens on an Olympus E-P1 using an adapter and noticed that the image seems more tightly framed and the depth of field appears greater.

I understand that the smaller Micro Four Thirds sensor changes the field of view because it captures a smaller central portion of the lens’s image circle. Does the adapter also affect this by changing the lens-to-sensor distance, or should that stay the same?

Why does depth of field appear larger on the smaller sensor, and are there any other optical characteristics that change when you use the same lens on a different camera body? I’m asking about optical behavior, not feature compatibility like autofocus.

Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

15y ago

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The lens properties stay exactly the same. However, you might record the image differently.

Sensor size is going to be the biggest factor, as you noticed, as it affects both field of view and depth of field.

And since you're recording a smaller area in the center of the image circle, you're (probably — individual results may vary) getting the best part of the lens, and corner softness and possibly vignetting won't be as significant.

The smaller sensor doesn't inherently increase magnification. If you're printing the resulting image at the same size, that'll require you to magnify it more, but the size of the image projected by the lens remains the same.

The distance to the sensor is the focal length of the lens, and this doesn't change. Or it shouldn't — some combinations of camera mounts and lenses make adapters which put the lens in exactly the right place impossible, so focal length will change slightly and you'll probably lose the ability to focus at infinity (and possibly be able to focus a bit closer, which will increase magnification). This shouldn't be the case with Nikon lenses adapted to micro four thirds, though — the flange distance is so small that there's plenty of room for an adapter.

Other things, of course, will depend simply on the different properties of the sensor — depending on the camera, the photosites might be closer together, for example, and Nikon and Olympus are going to render colors somewhat differently. None of that is the lens itself, though.

Originally by user1943. Source · Licensed CC BY-SA 4.0

user1943

15y ago

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AI Answer

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The lens’s own optical properties do not change just because you mount it on a different camera. A 50mm lens is still a 50mm lens, and its image projection is the same.

What changes is how much of that image the sensor records. A smaller sensor captures a smaller central area of the image circle, so the field of view becomes narrower (often described as a crop). The sensor does not create extra magnification in the lens itself.

An adapter should preserve the correct flange distance. If it is properly made, it does not change focal length or magnification; it just positions the lens at the right distance from the sensor.

Depth of field appears greater on the smaller sensor mainly because, to get the same final image size or framing comparison, the smaller-sensor image is enlarged more and/or you stand farther back or use a shorter lens for the same composition. Also, using only the center of the image circle often reduces visible corner softness and vignetting, since you’re avoiding the outer edges of the lens’s projection.

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