Poor Man's Optical Bench: Macro Update

Just a quick update on my Poor Man's Optical Bench simulator, that you can access from the right hand link.

In addition to a few UI tweaks, such as being able to show an outline of the lens and camera, after entering a few basic dimensions, I've added an extension tube simulation.

Once you have set up the non-extended lens (see previous posts), all you need to do is to add in the extension length you are using, and the simulator will give you an estimate of the new magnification.

Knowing this, you can then return to page 1 and click the link to Zerene Stacker's DoF calculator.

As the ZS site says: “the Zerene Stacker includes a unique macro/micro depth-of-field calculator that combines both diffraction blur and classic circle-of-confusion. 

Very briefly, the wave optics calculation is done by using the diffraction limited criterion of 1/4-lambda wavefront error. That allows the MTF curve to sag a little bit at worst defocus, but does not change the cutoff frequency. The classic calculation uses standard geometric optics, starting with a specified diameter for the allowed circle of confusion (CoC). The calculator then recommends the larger of the two resulting DOF values, on the rationale that if you specified an acceptable CoC then you must be willing to accept at least that much blur, and if the specified aperture allows a larger step size due to diffraction, then you should use that larger value.

The two calculations end up producing almost the same number when CoC = 0.0011 * effective F-number. Through no coincidence at all, 0.0011 * effective F-number also corresponds to the size of the Airy disk at that aperture. In other words, the wave optics calculation is “just like” running the classic calculation, with a CoC that is automatically matched to the size of the diffraction blur.”