Well I changed my phone a while ago and have recently needed the Depth of field calculator and it was not there. So I wrote one... I have already written a similar one in Python for S60, so the logic remains the same, I just had to redo the GUI part, which uses Python with GTK and Hildon modules.
This is the screenshot of the results window:
The old post (which contains the apps for Symbian S60 Python is available here
The web site where you can download the files is here
If you find it useful or if you find any bugs, please drop me a note.