Smaller Aperture

The N value is doubled for this image. Since the original N is 3.5, and since there isn't an f-stop of 7, I assumed that f/6.3 is double.

 

DOF Calculation

(2CNU^2)/(f^2)

C= 0.018mm

N= 6.3mm

U=615mm

F= 18*1.5 (accounting for a crop factor) = 27mm

 

(2(0.018)(6.3)(615)^2)/((18*1.5)^2)

 

(2*0.018*3.5*615^2)/(27^2) = 117.67 mm = 11.76 cm

This is the Horizontal DOF. The ruler was slanted at a 45-degree angle. Accounting for this the actual result is 11.76 * sqrt(2) = 16.63 cm.

 

This makes sense because more of the image is in focus

Done