T3D Re: DOF spreadsheet explanation

[Bill Costa -- Network Info Srvs <bill.costa@xxxxxxx>]

     John Bercovitz <bercov@xxxxxxxxxxx> recently posted (in part) to
     Tech-3D

> Most DOF calculators are based on viewing a print from a fixed distance
> regardless of focal length of lens.  So they set the fuzziness of a 
> print in lines per mm.  Therefore, these DOF programs aren't applicable 
> in 3D which uses center of perspective viewing.

     I guess I don't understand what "center of perspective viewing"
     means.  Do you have a pointer to an explaination of this concept?

> Do you happen to know the basis of the program you mention above?

     From the help file:

> Note:
> 
> All distances are measured from the optical center of the lens, normally 
> located somewhere near its front element.
> 
> Technical Notes:
> 
> This program computes depth of field according to the following 
> formulas:
> A = circle of confusion = 1/resolution
> D = distance at which lens is focused
> F = lens focal length
> N = f stop
> G = N*A
> H = (F*F)/G
> near focus = (D*H)/(H+D-F)
> far focus = (D*H)/(H+F-D)
> hyperfocal distance = H + F
> 
> Acknowledgements:
> 
> Depth of field formulas follow those derived by Nick Sushkin (see 
> http://oh114.wpi.edu/cgi-bin/htdof) as modified by Harold M. Merklinger, 
> author of The Ins and Outs of Focus, available from the author at:
> 
> Harold M. Merklinger
> P.O. Box 494
> Dartmouth  NS
> Canada B2Y 3Y8.


     John also wrote in a separate message:

> I tried downloading this to my PC (Pentium, Win 95) and when I 
> tried to run it, a DOS window flashed on the screen for a few 
> milliseconds and went away.

     Is the problem unpacking the zip file, or running the program
     itself.  Here's what I got for files when I unpacked the 
     distribution:

DOF.EXE   39,424 bytes
DOF.HLP   17,067 bytes

     When I click on the DOF executable icon, a new window appears
     immediately and the program has no problem finding its help
     file.  I just unpacked this stuff in a temp directory on my
     `user' partition.  No paths are set to this area, so I don't
     think you should have to make any special settings to get
     it run.

     Before you go to a lot of trouble trying to install it, here's
     what the program looks like (as an ASCII picture):

     +---
                Focal Length: [ 50.0    ]  [mm|v]
                      F Stop: [ 16.00   ]
                  Resolution: [ 30.0    ]  [lines/mm|v]
                    Focus At: [ 5.000   ]  [ft|v]

                  Near Focus: 3.804 ft
                   Far Focus: 7.293 ft
         Hyperfocal Distance: 15.543 ft

           [ Compute ]    [ Help ]   [ Exit ]
     +---


     The drop down menu for the focal length gives a choice of units:

                 mm, cm, in, ft, m

     for resolution:
     
                 lines/mm, lines/cm, lines/in, lines/ft, lines/m

     etc.

     If anybody would like a copy of the help file as plain text via
     e-mail, let me know.

                                                       Later....BC

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| Bill Costa                                          |
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