Re: DOF/Dr. T/Merklinger Book - Oops!

[P3D John Bercovitz <bercov@xxxxxxxxxxx>]

> One in 3400 is probably overdoing it 8-) if your film/lens will only support
> 40 lines per mm and you're in 5P using, say, a 35 mm lens.  40*35= 1400
> so not going past one part in 1400 for your C of C would be reasonable.
> 
> One part in 1400 is 147" of arc so referring back to my earlier post,
> 
> D = 115/R = 115/147 = 0.8 mm
>  
> Lens focal length     f/number for 0.8 mm aperture
>  
>       35                         44
>       50                         62
>       80                        100
>      150                        190

I sorta ignored the system res (I used 40 lines per mm) changing with the 
format.  8*)  If your 6x7 only gets 30 lines per mm, then 30*80 = 2400
and one part in 2400 is 86" of arc.  If your Spud only gets 20, you have
another problem.  Also, what part of the field do you want to concern 
yourself with?  The triplets tend to have pretty poor resolution in their 
corners compared to their centers.  So let me try again:

Res-driven relative apertures

Lens focal length    res, lpmm         f/number 
 
      35              30 to 50         60 to 36
      50                 60               30
      80              20 to 40         90 to 45
     150                 25               72

John B


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