Narrow DOF

Update -- I took a pic of this ruler (metric of course) and you can clearly see the tiny DOF. Considering the trig (I was about 45 degrees) I think the DOF is under 1mm actually. This is at f = 1/2.8 and near minimum focal length for the lens. I need to think more about the math to see if the observed DOF aligns with the theory. Recall that the f number is 1 / (2 * NA). So the NA is ~ 0.18. DOF ~ wavelength / NA^2, so lets see, wavelenth ~ 0.5um, gives a DOF of only 15um, but the pic really shows quite a bit more than that, seems like at least 500um. I need to think about it some more I guess.



Here is a picture of our outdoor table top. Tiny depth of focus with this high magnification and high NA system :) Maybe only ~1mm of DOF...

Hrm, wiki time later... dof ~2 * f # * circle of confusion * (1 + mag ) / mag ^ 2

So, for my camera, the circle of confusion appears to be ~ 18um, again f was 2.8 for these pics and I was as close as possible, so the mag was actually 1.

So, dof ~ 200um. Yeah, that seems to be a little closer to my observation.