P3D Hyperfocal distances - differences

["Dr. George A. Themelis" <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Bill Stickley writes:

>Your post started me thinking and looking at two Realists I have
>(one a 2.8 and the other a 3.5 with DEP and DOF scale). I was
>trying to find a way to use Hyper focal without memorizing or
>taking one more sheet with me. It is interesting in that if you
>simply set the focus to infinity for the selected aperture, the
>focus distance reads fairly close but not exactly as what you
>posted. 

Oh, YES!  You just discovered the UNIVERSAL way to find the
hyperfocal distance using the depth of field (DOF) scales built
in your lens or camera.  It can be used with any modern lens with
DOF markings.

>Even more interesting is that the two cameras do NOT
>agree. Are there some differences in DOF scales or is it because
>of the differences in the 2.8 and 3.5 lenses? 

Only if the lenses have different focal lengths.  I think they are
both quoted to be 35 mm.

>    
>    Aperture  Focus at  Infinity point set  Infinity point set
>                        to aperture (2.8)   to aperture (3.5)
>    --------  --------  ------------------  ------------------
>      2.8       44 ft          35                      n/a
>      3.5       34             n/a                     35
>      4         30             25                      n/a
>      5.6       22             22                      25
>      8         25             14                      19
>     11         11             12                      14
>     16          8             9                       10
>     22        5.5        DOF scales do not go past f16

The small difference are due to the construction of the DOF scales.
Note there are no lines marking the apertures.  So when you try
to align the infinity with a specific f-stop, you don't know where
exactly is the f-stop.  So, I cannot figure out how you came up
with 35 ft at 2.8 when the pointer is between 25 ft and infinity.
Are you a phycic? :-)

Overall, the differences are too small for me to worry. 

Furthermore, some earlier Realists use a *different* hyperfocal
scale.  A sticky issue, discussed earlier in photo-3d. I assume
a different size for the circle of confusion was used but I don't
know why.  Kodak is also known to have a totally inaccurate DOF
scale so that it looks better? (this is my recollection from what
I have read - no personal experience).

George Themelis



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