A Background OOF Calculator

[xpatUSA]

A recent discussion prompted this thread. Some time ago I wrote a spreadsheet that calculates the diameter of a blur circle at the sensor, assuming a point source of light some distance away:



Three kinds of file (.xls, .ods, .slk) for downloading can be found here:

http://kronometric.org/phot/blur%20diameter/

The data to be entered is in the yellow boxes - all others are calculated.

The distances to be entered are from the sensor mark on top of the camera.

The cells values are unprotected - typing data accidentally into a green box will mess it up.

The result is only for 3:2 aspect ratio captures ... cropping may be OK.

Formulae are based on work by Merklinger and by Lyon.

The aperture is assumed to be perfectly round.

I developed this while trying to assess the bokeh from an old Carl Zeiss Jena lens.

[Manfred M]

All very interesting, but I thought size of the final image / viewing distance were also required.

Nicely said, something that is out of focus will seem to be sharp if it is small enough or viewed from far enough away.

[xpatUSA]

All very interesting, but I thought size of the final image / viewing distance were also required.

You appear to be confusing it with DOF calculations. My OOF blur circle in the image plane is not a circle of confusion. Think of it as a bokeh diameter.

Nicely said, something that is out of focus will seem to be sharp if it is small enough or viewed from far enough away.

Nicely agreed but that has nothing to do with the purpose of my calculator.

[Manfred M]

In that case, Ted, I did not understand the purpose of your calculator.

I now have a better idea as it has more to do with the quality of capture at the sensor level than final image quality.

[xpatUSA]

I now have a better idea as it has more to do with the quality of capture at the sensor level than final image quality.

Not really, Manfred. I am talking about how to get a particular desired quality of blur, namely how big it is in the final image relative to the in-focus subject (if there is one, -there doesn't have to be). I should have made that more clear, I suppose. In the image plane, the "quality" of deliberate blur suffers only when it's diameter in sensor pixels becomes too small - e.g. 1 pixel will a) not be blurred much and b) won't be round at all.

Hope this helps your understanding of the calculator's purpose.