# Rethinking 4/3 Depth Of Field

Started Apr 11, 2013 | Discussions thread
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Re: I'm thinking of topping myself ...

Michael J Davis wrote:

...yet another DoF thread & more nonsense!

... I expect!

So true, Michael. All that exists is some perceptual Circle of Confusion from which extrapolations are made to and fro in object-space. In the end, likely nearly all just guess in the field (and/or believe preview-screens). Once again, the deeply complicated extrapolations (for all but close-up/macro):

Hyperfocal Distance (in units of Meters):

HFD = (L^2 / (FC) ) + L

where:

L is the Focal Length (in units of milliMeters);

F is F-Number;

C is COC diameter (in units of Microns)

.

Depth of Field (in units of Meters):

DOF = (2D) / ( HFD/D - D/HFD )

where:

D is Camera to Subject Distance (front nodal plane to plane of focus);

HFD is Hyperfocal Distance.

.

Approximate DOF (maximum 11% error on the low side at 1/3 of the Hyperfocal Distance):

DOF ~ (2FC) * (D/L)^2

where:

F is F-Number;

C is COC diameter (in units of Microns);

D is Camera to Subject Distance (front nodal plane to plane of focus);

L is the Effective Focal Length (in units of milliMeters).

.

Relative Background Blur:

BP ~ ( (100) / ( (F) (H) ) ) * ( (L)^(2) ) * ( ( Df - D ) / ( (Df) (D) ) )

where:

BP is the percentage of the image-frame diagonal that the blur-disk represents;

F is F-Number;

H is the diagonal dimension of the image-sensor's active-area;

L is the Focal Length (when focused at infinity);

D is the Camera (front nodal-plane) to Subject (plane-of focus) Distance;

Df is the Camera (front nodal-plane) to Background Subject Matter Distance.

.

Under Constant Framing (FOV) Conditions (when D is the same; when Df and D are the same):

DOF2 / DOF1 = ( F2 / L2) / ( F1 / L1 ) = A2 / A1

BP2 / BP1 = ( F1 / L1 ) / ( F2 / L2) = A1 / A2

where A is the virtual aperture (entrance pupil) diameter.

.

Under Constant DOF Conditions:

The virtual aperture (entrance pupil) diameter being the same, the Total Light is the same, and different sensor sizes perform the same - except Photon Shot Noise will vary by the square-root of the Quantum Efficiencies, and Read Noise will vary in ways determined more by the image-sensor's individual design than other factors (which makes comparisons largely camera test-data specific).

.

Now that the mathematics and sensor process variables prove to be either too formidable, or unknown without test data, we can go back to guessing and peering at tiny preview-screens.

DM ...

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