4/3rds DOF Q?

[richpips]

OK, I understand that the depth of field value is doubled with 4/3rds lenses meaning a larger area is in focus, or near focus. eg f/1.4 on 4/3rds equates to f/2.8 on full frame

Am I right in thinking that for a given aperture eg f/1.4, though that same amount hits a sensor irrespective of the camera format ie full frame, aps-c, 4/3 ?

Rich

 

[dazzajl]

You are right.

In fact, technically speaking the DoF doesn't change across formats at all. A 20mm lens is the same optical being regardless of the sensor or film behind it.

What makes the change is the fact that to create images with similar framing across different formats, you need to move nearer or further from the subject and distance to subject does of course affect DoF.

 

[richpips]

You are right.

In fact, technically speaking the DoF doesn't change across formats at all. A 20mm lens is the same optical being regardless of the sensor or film behind it.

What makes the change is the fact that to create images with similar framing across different formats, you need to move nearer or further from the subject and distance to subject does of course affect DoF.

Thanks for confirming that.

 

[incapete]

Thanks for confirming that.

Wish we had a 'thanks' button available...



Seriously though, that's a great explanation of a feature of crop format sensors that I knew and accepted but had never really worked out why.

So if you were to stand still and take a shot with a full-frame and one with a crop, using the same lens then you'd obviously have large differences in framing but the depth-of-field in both images would be the same? And if I cropped the images to replicate their framing they would both look the same (resolution apart)?

 

[karmagarda]

Wish we had a 'thanks' button available...



Seriously though, that's a great explanation of a feature of crop format sensors that I knew and accepted but had never really worked out why.

So if you were to stand still and take a shot with a full-frame and one with a crop, using the same lens then you'd obviously have large differences in framing but the depth-of-field in both images would be the same? And if I cropped the images to replicate their framing they would both look the same (resolution apart)?

 

[incapete]

Thought you'd like that

 

[HoppyUK]

You are right.

Yes, but I wouldn't call it doubling of DoF. It is increased by two stops, which is not the same thing.

In fact, technically speaking the DoF doesn't change across formats at all. A 20mm lens is the same optical being regardless of the sensor or film behind it.

DoF does change with format, because when you change format you have to change focal length to retain framing - the format is key and drives everything. And the degree of enlargement also changes, affecting DoF (smaller format has to be enlarged more, requiring a smaller circle of confusion to maintain equality).

What makes the change is the fact that to create images with similar framing across different formats, you need to move nearer or further from the subject and distance to subject does of course affect DoF.

To retain framing, you don't move nearer or further away as that would change perspective. To record the same image like for like, on 4/3rds you have to half the focal length, and lower the f/number by two stops (relative to full frame).

So if you were to stand still and take a shot with a full-frame and one with a crop, using the same lens then you'd obviously have large differences in framing but the depth-of-field in both images would be the same?

No, because the size of the subject (magnification) would be different (assuming you printed them both to the same size).

And if I cropped the images to replicate their framing they would both look the same (resolution apart)?

Yes, because the magnification would be the same.