DoF JSON online calculator

DOF JSON 2 DoF JSON online calculator
Click the image to go to the Dof-JSON application

This is a DoF (photography depth of field) calculator implemented as a web service. The input and output are arranged in JSON format. The input parameters are:

  • m : sensor resolution.  Number of pixels in which the sensor is divided along its longer side. In terms of the circle of confusion (CoC) this would be: m = (Length of sensor) / (Circle of Confusion). (We choose 1250 as default value, which corresponds to a CoC of 0.028 mm)
  • S : length of the (longer side of the) sensor in milimeters
  • f : f-number of the lense ( f = (Focal length in mm) /  (Aperture of the lense in mm)
  • F : focal length in mm
  • x0 : focused distance in meters

The output parameters:

  • x_near : focused region’s near limit (meters)
  • x_far : focused region’s far limit (meters)
  • DOF : depth of field (meters). DOF = x_far – x_near
  • H  : hyperfocal distance (meters)

The calculator receives the queries in JSON format through a POST request (triggered by the form in the app page). The two sliders are meant to smoothly modify the focused distance and the f-number through websockets. However, the web service is hosted in Heroku, which does not support websockets on his current cedar stack. Xhr-polling is used instead, so the final outcome is that the sliders behave sort of sluggishly.

Updated (23-October-2013) – Heroku: WebSockets now in public beta

Heroku has recently announced that WebSockets are supported now in beta version.

Following the guidelines in the Heroku dev center, we have activated them for the DoF JSON online calculator. The sliders behave now quite smoothly.


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